Anatomy 2

The liver receives blood from

two sources (Figure 24.15). From the hepatic artery it obtains oxygenated blood, and from the he- patic portal vein it receives deoxygenated blood containing newly absorbed nutrients, drugs, and possibly microbes and toxins from the gastrointestinal tract. Branches of both the hepatic artery and the hepatic portal vein carry blood into hepatic sinusoids, where oxygen, most of the nutrients, and certain toxic substances are taken up by the hepatocytes. Products manufactured by the hepatocytes and nutrients needed by other cells are secreted back into the blood, which then drains into the central vein and even- tually passes into a hepatic vein. Because blood from the gastroin- testinal tract passes through the liver as part of the hepatic portal circulation, the liver is often a site for metastasis of cancer that originates in the GI tract.

The stomach

typically a J-shaped enlargement of the GI tract directly inferior to the diaphragm in the epigastric, umbilical, and left hypochondriac regions of the abdomen (see Figure 1.8). The stomach connects the esophagus to the duodenum, the first part of the small intestine (Figure 24.10). Because a meal can be eaten much more quickly than the intestines can digest and absorb it, the stomach functions as a mixing area and holding reservoir. At appropriate intervals after food is ingested, the stomach forces a small quantity of material into the first portion of the small intes- tine. The position and size of the stomach vary continually; the diaphragm pushes it inferiorly with each inhalation and pulls it superiorly with each exhalation. The stomach is the most disten- sible portion of the GI tract and can accommodate a large quan- tity of food, up to 6.4 liters (6 qt.). In the stomach, the digestion of starch and triglycerides that began in the mouth continues, digestion of proteins begins, the semisolid bolus is converted to a liquid, and certain substances are absorbed.

principal cells

which have receptors for both antidiuretic hormone (ADH) and aldosterone, two hormones that regulate their functions.

nasal cavity

Deeper into the skull, beyond the region of the nasal vestibules, is the internal nose

primitive gut

During the fourth week of development, the cells of the endo- derm form a cavity called the primitive gut, the forerunner of the gastrointestinal tract (see Figure 4.12b). Soon afterward the meso- derm forms and splits into two layers (somatic and splanchnic), as shown in Figure 4.9d. The splanchnic mesoderm associates with the endoderm of the primitive gut; as a result, the primitive gut has a double-layered wall.

ovulation

During the reproductive years of a female, they produce secondary oocytes and discharge them into the peritoneal cavity each month

primordial follicle

During this arrested stage of development, each primary oocyte is surrounded by a single layer of flat follicular cells, and the entire structureprimordial follicles consists of collagen fibers and fibroblast-like stromal cells. At birth, approximately 200,000 to 2,000,000 pri- mary oocytes remain in each ovary. Of these, about 40,000 are still present at puberty, and around 400 will mature and ovulate during a woman's reproductive lifetime. The remainder of the primary oocytes undergo atresia. Each month after puberty until menopause, gonadotropins (FSH and LH) secreted by the anterior pituitary further stimu- late the development of several primordial follicles, although only one will typically reach the maturity needed for ovulation.

Functions of the Pancreas

Each day the pancreas produces 1200-1500 mL (about 1.2-1.5 qt) of pancreatic juice, a clear, colorless liquid consisting mostly of water, some salts, sodium bicarbonate, and several enzymes. The sodium bicarbonate gives pancreatic juice a slightly alka- line pH (7.1-8.2) that buffers acidic gastric juice in chyme, stops the action of pepsin from the stomach, and creates the proper pH for the action of digestive enzymes in the small intestine. The enzymes in pancreatic juice include a starch- digesting enzyme called pancreatic amylase; several enzymes that digest proteins into peptides called trypsin (TRIP-sin), chymotrypsin (kı ̄ -moˉ -TRIP-sin), carboxypeptidase (kar- bok -seˉ-PEP-ti-da ̄s), and elastase (eˉ-LAS-ta ̄s); the principal triglyceride (fat and oil)-digesting enzyme in adults, called pancreatic lipase; and enzymes called ribonuclease (rı ̄ - boˉ-NOO-kleˉ-a ̄s) and deoxyribonuclease (deˉ-oks-eˉ-rı ̄ -boˉ- NOO-kleˉ-a ̄s) that digest ribonucleic acid (RNA) and deoxyri- bonucleic acid (DNA) into nucleotides.

papillary ducts

Filtrate (filtered fluid) formed by the nephrons drains into large papillary ducts which extend through the renal papillae of the pyramids. The papillary ducts drain into cuplike structures called minor and major calyces

change from filtrate to urine

Filtrate contains everything that blood plasma does except blood proteins; but by the time filtrate has moved into the collecting ducts, it has lost most of its water, nutrients, and essential ions. When filtrate exits the collecting ducts into the calyces, it is called urine.

sper- miation

Finally, sperm are released from their connections toˉsustentacular cells, an event

minor alar cartilages

Finally, there are three or four small pieces of cartilage posterior to the major alar cartilages

body

Inferior to the fundus is the large central portion of the stomach

tunica albuginea

Internal to the visceral layer of the tunica vaginalis, the testis is surrounded by a white fibrous capsule composed of dense irregular connective tissue

renal fascia

The superficial layer, the renal fascia is another thin layer of dense irregu- lar connective tissue that anchors the kidney to the surrounding structures and to the abdominal wall. On the anterior surface of the kidneys, the renal fascia is deep to the peritoneum.

Bulbus cordis

Right ventricle

surface mucous cells

The surface of the mucosa is a layer of nonciliated simple columnar epithelial cells

Most of distal convoluted tubule (DCT)

Simple cuboidal epithelial cells

Proximal convoluted tubule (PCT)

Simple cuboidal epithelial cells with prominent brush borders of microvilli

Last part of DCT and all of collecting duct (CD)

Simple cuboidal epithelium consisting of principal cells and intercalated cells

Nephron loop: thick ascending limb

Simple cuboidal to low columnar epithelial cells

Nephron loop: descending limb and thin ascending limb

Simple squamous epithelial cells

spermatogonia

Starting at puberty, sperm production begins at the periphery of the seminiferous tubules in stem cells

Development of the Chorionic Villi and Placenta

The term organogenesis (or -ga-no ̄ -JEN-e-sis) refers to the formation of body organs and systems. By the end of the eighth week

hemopoiesis

The process by which the formed elements of blood develop

spermatogenesis

The process by which the seminifer- ous tubules of the testes produce sperm

adventitia

The superficial coat of the ureters is the adventitia, a layer of areolar connective tissue containing blood vessels, lymphatic vessels, and nerves that serve the muscularis and mucosa. The ad- ventitia blends in with surrounding connective tissue and anchors the ureters in place.

parietal pleura

The superficial layer of the pleural membrane lining the wall of the thoracic cavity

The duration of the female reproductive cycle typically ranges

from 24 to 35 days. For this discussion, we assume a duration of 28 days and divide it into four phases: the menstrual phase, the preovulatory phase, ovulation, and the postovulatory phase

rectum

approximately 15 cm (6 in.) in length, lies ante- rior to the sacrum and coccyx. The terminal 2-3 cm (1 in.) of the large intestine is called the anal canal (Figure 24.19b). The mucous membrane of the anal canal is arranged in longitudinal folds called anal columns that contain a network of arteries and veins. The opening of the anal canal to the exterior, called the anus, is guarded by an internal anal sphincter of smooth muscle (involuntary) and an external anal sphincter of skeletal muscle (voluntary). Nor- mally the anus is closed except during the elimination of feces.

The layers of the tracheal wall, from deep to superficial,

are (1) the mucosa, (2) the submucosa, (3) the fibro musculo cartilaginous layer, and (4) the adventitia.

Gastrin stimulates

growth of the gastric glands and secretion of large amounts of gastric juice. It also strengthens contraction of the lower esophageal sphincter, increases motility of the stomach, and relaxes the pyloric and ileocecal sphincters (described later).

sperm cell

has formed, it is released into the lumen of the seminiferous tubule.

mus- cularis

has three layers of smooth muscle (rather than the two found in the lower esophagus and small and large intestines): an outer longitudinal layer, a middle circular layer, and an inner ob- lique layer. The oblique layer is limited primarily to the body of the stomach. This arrangement of muscle allows the stomach to more effectively churn and mix the food.

white blood cells, or leukocytes

have a nucleus and a full com- plement of other organelles but they do not contain hemo- globin as either granular or agranular, depending on whether they contain conspicuous cytoplasmic granules that are made visible by staining when viewed through a light microscope.

muscular venules

have thicker walls across which exchanges with the interstitial fluid can no longer occur.

different decidua layers

he decidua basalis is the portion of the endometrium beneath the implanting embryo; it provides large amounts of glycogen and lipids for the developing embryo and fetus and later becomes the maternal part of the pla- centa. The decidua capsularis is the portion of the endometrium that will cover the embryo after it implants in the endometrium. The decidua parietalis (par-ri ̄-e-TAL-is) is the remaining mod- ified endometrium that lines the noninvolved areas of the rest of the uterus.

coronary (cardiac) circulation

he flow of blood through the many vessels that pierce the myocardium

corniculate cartilages

horn-shaped pieces of elastic cartilage, are located at the apex of each arytenoid cartilage. The paired cunei- form cartilages (KU ̄ -ne ̄-i-form wedge-shaped) are club-shaped elastic cartilages anterior to the corniculate cartilages at the lat- eral aspect of the epiglottis.

submucosa

consists of areolar connective tissue that contains seromu- cous glands and their ducts.

red pulp

consists of blood-filled venous sinuses and cords of splenic tissue called splenic cords or Billroth's cords. Splenic cords consist of red blood cells, macrophages, lymphocytes, plasma cells, and granulocytes. Veins are closely associated with the red pulp.

tunica externa

consists of elastic and collagenous fibers It ranges in size from a thin connective tissue wrapping to the thickest layer of the blood vessel. The tunica externa contains numerous nerves and, especially in larger ves- sels, tiny blood vessels that supply the tissue of the vessel wall.

lymphatic system

consists of four elements: a fluid called lymph, lymphatic vessels that transport the lymph, a number of structures and organs containing lymphocytes within a filtering tissue (lymphatic tissue), and red bone mar- row assists in circulating body fluids and helps defend the body against disease-causing agents.

myometrium

consists of three layers of smooth muscle fibers that are thickest in the fundus and thinnest in the cervix. The thicker middle layer is circular; the inner and outer layers are longitu- dinal or oblique. During labor and childbirth, coordinated con- tractions of the myometrium in response to stimulation by the hormone oxytocin from the posterior pituitary help expel the fetus from the uterus.

The mucosa consists of

epithelium and lamina propria (areolar connective tissue). The epithelium contains ciliated simple columnar cells, which function as a ciliary "conveyor belt" to help move a fer- tilized ovum (or secondary oocyte) within the tube toward the uterus, and nonciliated cells called peg cells, which have micro- villi and secrete a fluid that provides nutrition for the ovum

At ovulation, the secondary oocyte is

expelled into the perito- neal cavity together with the first polar body and corona radiata. Normally these cells are swept into the uterine tube. If fertili- zation does not occur, the cells degenerate. However, if sperm are present in the uterine tube and one penetrates the secondary oocyte, meiosis II resumes. The secondary oocyte splits into two haploid cells, again of unequal size. The larger cell is the ovum, or mature egg; the smaller one is the second polar body. The nuclei of the sperm cell and the ovum then unite, forming a dip- loid zygote. If the first polar body undergoes another division to produce two polar bodies, then the primary oocyte ultimately gives rise to three haploid polar bodies, which all degenerate, and a single haploid ovum. Thus, one primary oocyte gives rise to a single gamete (an ovum). By contrast, recall that in males one primary spermatocyte produces four gametes (sperm).

glans clitoris

exposed portion of the clitoris The glans clitoris is homologous to the glans penis in males. Like the male structure, the clitoris is capable of enlargement upon tactile stimulation and has a role in sexual excitement in the female.

trachea

extends from the larynx to the superior border of the fifth thoracic vertebra (T5), where it divides into the right and left main bronchi).

cheeks

form the lateral walls of the oral cavity. They are covered externally by skin and internally by a mucous membrane, which consists of nonkeratinized strati- fied squamous epithelium. Buccinator muscles and connective tissue lie between the skin and mucous membranes of the cheeks. The anterior portions of the cheeks end at the lips.

paired major alar cartilages

form the sides of the inferior por- tion of the external nose. They are connected to the lateral nasal cartilages and septal nasal cartilage. The major alar cartilages form the medial and lateral borders of the nostrils. When the muscles of the nose contract and relax, the major alar cartilages dilate and constrict the nostrils.

pontine respiratory group

formerly called the pneumotaxic center, is a collection of neurons in the pons (see Figure 23.13a). The neurons in the PRG are active during inhalation and exhalation. The PRG transmits nerve im- pulses to the DRG in the medulla. The PRG may play a role in both inhalation and exhalation by modifying the basic rhythm of breathing by the DRG, for example, when exercising, speaking, or sleeping. Roles of the medullary respiratory center in controlling (a) the basic rhythm of breathing and (b) forceful breathing. During normal quiet breathing, the ventral respiratory The respiratory center is composed of neurons in the medullary respiratory center in the medulla oblongata plus the pontine respiratory group in the pons. group is inactive; during forceful breathing the dorsal respiratory group activates the ventral respiratory group.

vagi- nal orifice

forms a border around and partially closes the inferior end of the vaginal opening to the exterior

unpaired septal nasal cartilage

forms the anterior portion of the nasal septum, a partition that divides the external and internal nose into right and left chambers). The septal nasal cartilage is connected to the perpendicular plate of the ethmoid and vomer to form the remainder of the nasal septum. It is also connected to the nasal bones and the lateral nasal cartilages. The paired lateral nasal cartilages form the sides of the midportion of the external nose. They are connected to the nasal bones, max- illae, septal nasal cartilage, and major alar cartilages

tunica interna (intima)

forms the inner lining of a blood vessel and is in direct contact with the blood as it flows through the lumen (LOO-men), or interior opening, of the ves- sel Its innermost layer is called endothelium, which is continuous with the endocardial lining of the heart.

FSH

in turn initiates follicular growth and the secretion of estrogens by the growing ovar- ian follicles.

• Primary sexual characteristics

internal and external organs

Ingestion

involves taking foods and liquids into the mouth (eating).

urinary bladder

is a hollow, distensible muscular organ situated in the pelvic cavity posterior to the pubic symphysis. In males, it is directly anterior to the rectum; in females it is anterior to the vagina and inferior to the uterus). It is held in position by folds of the peritoneum. The shape of the uri- nary bladder depends on how much urine it contains.

relaxin

is a hormone produced by the ovary and the placenta with important effects in the female reproductive system and during pregnancy. In preparation for childbirth, it relaxes the ligaments in the pelvis and softens and widens the cervix.

The prostatic urethra contains the openings of

of (1) ducts that trans- port secretions from the prostate and (2) the seminal vesicles that provide secretions that both neutralize the acidity of the female reproductive tract and contribute to sperm motility and viabil- ity, and the ductus (vas) deferens, which deliver sperm into the urethra.

tail

of a sperm is subdivided into four parts: neck, middle piece, principal piece, and end piece. The neck is the constricted re- gion just behind the head that contains centrioles. The centri- oles form the microtubules that comprise the remainder of the tail. The middle piece contains mitochondria arranged in a spi- ral, which provide the energy (ATP) for locomotion of sperm to the site of fertilization and for sperm metabolism. The princi- pal piece is the longest portion of the tail and the end piece is the terminal, tapering portion of the tail. Once ejaculated, most sperm do not survive more than 48 hours within the female re- productive tract.

Cervical mucus is more hospitable to sperm at or near the time

of ovulation because it is then less viscous and more alkaline (pH 8.5). At other times, a more viscous mucus forms a cervical plug that physically impedes sperm penetration. Cervical mucus supplements the energy needs of sperm, and both the cervix and cervical mucus protect sperm from phagocytes and the hostile environment of the vagina and uterus. They may also play a role in capacitation (ka-pas -i-TAˉ -shun)—a functional change that sperm undergo in the female reproductive tract before they are able to fertilize a secondary oocyte. Capacitation causes a sperm cell's tail to beat even more vigorously and it prepares the sperm cell's plasma membrane to fuse with the oocyte's plasma membrane.

The nerve supply to the liver consists

of parasympathetic in- nervation from the vagus (X) nerves and sympathetic innervation from the greater splanchnic nerves through the celiac ganglia.

The submandibular glands consist mostly

of serous acini (serous-fluid-secreting portions of gland) and a few mucous acini (mucus-secreting portions of gland). The parotid glands consist of serous acini only. The sublingual glands consist of mostly mu- cous acini and a few serous acini.

The nerves to the large intestine consist

of sympathetic, para- sympathetic, and sensory components. The sympathetic inner- vation arises from the celiac, superior, and inferior mesenteric ganglia and superior and inferior mesenteric plexuses. The fibers reach the viscera by way of the thoracic and lumbar splanchnic nerves. The parasympathetic innervation is derived from the vagus (X) and pelvic splanchnic nerves. Similar to its function in the vascular supply, the left colic flexure serves as the transition zone between vagal and pelvic splanchnic innervation.

Absorptive cells

of the epithelium release enzymes that digest food and contain microvilli that absorb nutrients in the small intestine

In females, the reproductive cycle normally occurs once each month from

menarche (me-NAR-keˉ), the first menses, to meno- pause, the permanent cessation of menses. Thus, the female repro- ductive system has a time-limited span of fertility between menarche and menopause. For the first 1 to 2 years after menarche, ovulation occurs in only about 10 percent of the cycles and the luteal phase is short. Gradually, the percentage of ovulatory cycles increases, and the luteal phase reaches its normal duration of 14 days. With age, fertility declines. Between the ages of 40 and 50 the pool of remain- ing ovarian follicles becomes exhausted. As a result, the ovaries be- come less responsive to hormonal stimulation. The production of estrogens declines, despite copious secretion of FSH and LH by the anterior pituitary. Many women experience hot flashes and heavy sweating, which coincide with bursts of GnRH release. Other symp- toms of menopause are headache, hair loss, muscular pains, vaginal dryness, insomnia, depression, weight gain, and mood swings. Some atrophy of the ovaries, uterine tubes, uterus, vagina, external geni- talia, and breasts occurs in postmenopausal women. Due to loss of estrogens, most women experience a decline in bone mineral den- sity after menopause. Sexual desire (libido) does not show a parallel decline; it may be maintained by adrenal sex steroids. The risk of having uterine cancer peaks at about 65 years of age, but cervical cancer is more common in younger women.

The heart begins its development from

mesoderm on day 18 or 19 following fertilization.

ultimate kidney

metanephros (met- a-NEF-roˉs; meta- after), or ultimate kidney, develops from the ureteric bud and metanephric mesoderm. The ureteric bud forms the collecting ducts, calyces, renal pelvis, and ureter. The metane- phric mesoderm (met -a-NEF-rik) forms the nephrons of the kidneys. By the third month, the fetal kidneys begin excreting urine into the surrounding amniotic fluid; indeed, fetal urine makes up most of the amniotic fluid.

root of the penis

penis is the attached portion (proximal portion). It consists of the bulb of the penis, the expanded posterior continuation of the base of the corpus spongiosum penis, and the crura of the penis (KROO-ra; singular is crus resembling a leg), the two separated and tapered continua- tions of the corpora cavernosa penis. The bulb of the penis is attached to the inferior surface of the deep muscles of the peri- neum and is enclosed by the bulbospongiosus muscle. Contrac- tion of the bulbospongiosus muscle aids ejaculation. Each crus of the penis bends laterally away from the bulb of the penis to attach to the ischial and inferior pubic rami and is surrounded by the ischiocavernosus

cremaster

move scrotum regulate temperature

After ovulation, local currents are produced by

movements of the fimbriae, which surround the surface of the mature follicle just before ovulation occurs. These currents sweep the ovulated secondary oocyte from the peritoneal cavity into the uterine tube. A sperm cell usually encounters and fertilizes a secondary oocyte in the ampulla of the uterine tube, although fertilization in the peritoneal cavity is not uncommon. Fertilization can occur up to about 24 hours after ovulation. Some hours after fertilization, the nuclear materials of the haploid ovum and sperm unite.

the uterine tubes are composed of three lay- ers:

mucosa, muscularis, and serosa

The gastric glands contain three types of exocrine gland cells that secrete their products into the stomach lumen:

mucous neck cells, chief cells, and parietal cells.

distributing arteries

muscular arteries continue to branch and ultimately distribute blood to each of the various organs

myometrium

muscular layer

The epithelium in the mouth, pharynx, esophagus, and anal canal is mainly

non keratinized stratified squamous epithe- lium that serves a protective function. Simple columnar epi- thelium, which functions in secretion and absorption, lines the stomach and intestines. Neighboring simple columnar epithelial cells are firmly sealed to one another by tight junc- tions that restrict leakage between the cells. The rate of re- newal of GI tract epithelial cells is rapid: Every 5-7 days they slough off and are replaced by new cells. Located among the absorptive epithelial cells are exocrine cells that secrete mu- cus and fluid into the lumen of the tract, and several types of endocrine cells, collectively called enteroendocrine cells (en -ter-oˉ-EN-doˉ-krin), which secrete hormones.

Parietal cells

produce intrinsic factor (needed for absorption of vitamin B12) and hydrochloric acid.

priapism

refers to a persistent and usually painful erection of the penis that does not involve sexual desire or excitement. The condition may last up to several hours and is accompanied by pain and tenderness. It results from abnor- malities of blood vessels and nerves, usually in response to medi- cation used to produce erections in males who otherwise cannot attain them. Other causes include a spinal cord disorder, leukemia, sickle-cell disease, or a pelvic tumor.

androgen

s a hormone that pro- motes the development of masculine characteristics.

progesterone

s an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species.[11] It belongs to a group of steroid hormones called the progestogens,[11] and is the major progestogen in the body. Progesterone is also a crucial metabolic intermediate in the production of other endogenous steroids, including the sex hormones and the corticosteroids, and plays an important role in brain function as a neurosteroid.[12]

The fluids secreted by the buccal glands, minor salivary glands, and the three pairs of major salivary glands constitut

saliva. The amount of saliva that is secreted daily varies considerably but

aldosterone

the main mineralocorticoid hormone, is a steroid hormone produced by the zona glomerulosa of the adrenal cortex in the adrenal gland.[1][2] It is essential for sodium conservation in the kidney, salivary glands, sweat glands and colon.[3] It plays a central role in the regulation of the plasma sodium (Na+), the extracellular potassium (K+) and arterial blood pressure.

The second kidney

the mesonephros (mez -oˉ -NEF-roˉ s; meso- middle), replaces the pronephros. The retained por- tion of the pronephric duct, which connects to the mesoneph- ros, develops into the mesonephric duct. The mesonephros begins to degenerate by the sixth week and is almost gone by the eighth week. At about the fifth week, a mesodermal outgrowth, called a ureteric bud (u ̄-re-TER-ik), develops from the distal portion of the mesonephric duct near the cloaca.

The diaphragm

the most important muscle of inhalation, is a dome-shaped skeletal muscle that forms the floor of the thoracic cavity. It is innervated by fibers of the phrenic nerves, which emerge from both sides of the spinal cord at cervical levels 3, 4, and 5. Contraction of the diaphragm causes it to flatten, lowering its dome. This increases the ver- tical diameter of the thoracic cavity and accounts for the movement of about 75 percent of the air that enters the lungs during normal quiet inhalation. The distance the diaphragm moves during inspiration ranges from 1 cm (0.4 in.) during normal quiet breathing up to about 10 cm (4 in.) during strenuous exercise. Advanced pregnancy, excessive obesity, or confining abdominal clothing can prevent a complete de- scent of the diaphragm. At the same time the diaphragm is contracting, the external intercostals are at their most active stage (these muscles contract during all phases of breathing).

Neurulation

the notochord also in- duces ectodermal cells above it to form the neural plate (Figure 4.9a). By the end of the third week the neural plate begins the process of invagination (in-vaj-in-NA ̄ -shun), an infolding of the ectoderm neural plate cells into the underlying mesoderm. During this process, the lateral edges of the neural plate become more elevated and form the neural folds (Figure 4.9b). The de- pressed region or groove between the neural folds is called the neural groove (Figure 4.9c). As the fold deepens, the neural folds approach each other and fuse, closing the neural groove and converting the neural plate into a neural tube that is pushed beneath the surface ectoderm into the underlying mesoderm (Fig- ure 4.9d). Neural tube cells then develop into the brain and spinal cord. The process of formation of the neural plate, neural folds, and neural tube is called neurulation (noor-oo-LA ̄ -shun). The notochordal process develops from the primitive node and later becomes the notochord. As the neural tube forms, some of the ectodermal cells migrate dorsolaterally to form several layers of cells called the neural crest. This population of cells is more extensive in the head end of the embryo where it forms a large mass of cells dorsolateral to the neural tube. Neural crest cells form all the sensory neurons and postganglionic motor neurons of the peripheral nerves, adre- nal medullae, melanocytes (pigment cells) of the skin, the arach- noid mater and pia mater of the brain and spinal cord, and almost all of the skeletal and connective tissue components of the head. Approximately four weeks after fertilization, the head end of the neural tube develops into three enlarged areas called primary brain vesicles (see Figure 18.1). The parts of the brain that develop from the various brain vesicles are described in Section 18.1.

cervical canal.

interior of the narrow cervix

The weight of the penis is supported by two ligaments that are continu- ous with the fascia of the penis:

(1) The fundiform ligament (FUN-di-form) arises from the inferior part of the linea alba; (2) the suspensory ligament of the penis arises from the pubic symphysis.

The male urethra, which also consists of a deep mucosa and a superficial muscularis, is subdivided into three anatomical re- gions:

(1) The prostatic urethra passes through the prostate; (2) the intermediate (membranous) urethra, the shortest portion, passes through the deep perineal muscles; and (3) the spongy urethra, the longest portion,

Anatomical subdivisions of the uterus include the following

(1) a dome-shaped portion superior to the uterine tubes called the fundus, (2) a tapering central portion called the body, and (3) an inferior narrow portion called the cer- vix that opens into the vagina. Between the body of the uterus and the cervix is the isthmus, a constricted region about 1 cm (0.5 in.) long.

Lateral to the base of the uvula are two muscular folds that run down the lateral sides of the soft palate:

(1) anteriorly, the palatoglossal arch (pal-a-toˉ- GLOS-al) extends to the side of the base of the tongue; (2) pos- teriorly, the palatopharyngeal arch (pal-a-toˉ -fa-RIN-jeˉ -al) ex- tends to the side of the pharynx. The palatine tonsils are situated between the arches, and the lingual tonsils are situated at the base of the tongue. At the posterior border of the soft palate, the mouth opens into the oropharynx through the fauces

The pharynx can be divided into three anatomical regions:

(1) nasopharynx, (2) oropharynx, and (3) laryngopharynx

In the order that fluid (filtrate) passes through them, the renal tubule consists of a

(1) proximal convoluted tubule (PCT) (kon -voˉ-LOOT-ed), (2) nephron loop (loop of Henle), and (3) distal convoluted tubule (DCT). Proximal denotes the part of the tubule attached to the glomerular capsule, and distal denotes the part that is farther away. Convoluted means the tubule is tightly coiled rather than straight. The renal corpuscle and both con- voluted tubules lie within the renal cortex; some nephron loops remain in the renal cortex and some extend into the renal medulla, make a hairpin turn, and then return to the renal cortex.

Within the red pulp, the spleen performs three functions related to blood cells:

(1) removal by macrophages of ruptured, worn out, or defective blood cells and platelets; (2) stor- age of platelets, up to one-third of the body's supply; and (3) pro- duction of blood cells (hemopoiesis) during fetal life

The four layers of the tract, from deep to superficial, are

(1) the mucosa, (2) the submucosa, (3) the muscularis, and (4) the serosa/adventitia

Normal exhalation during quiet breathing depends on two factors:

(1) the recoil of elastic fibers that were stretched during inhalation and (2) the inward pull of surface tension due to the film of alveolar fluid.

Structurally, the respiratory system consists of two parts:

(1) the upper respiratory system includes the nose, nasal cavity, pharynx, and associated structures; (2) the lower res- piratory system includes the larynx, trachea, bronchi, and lungs.

germinal epithelium

) is a layer of simple epithelium (low cuboidal or squamous) that covers the surface of the ovary. It is continuous with the mesothelium of the mesovarium and peritoneum. We now know that the term germinal epithelium is inappropriate because the cells of this tissue do not give rise to ova, but at one time people be- lieved that it did. We have since learned that the cells that pro- duce ova arise from the endoderm of the yolk sac and migrate to the ovaries during embryonic development.

prostate

) is a single, doughnut-shaped gland about the size of a ping-pong ball. It measures about 4 cm (1.6 in.) from side to side, about 3 cm (1.2 in.) from top to bottom, and about 2 cm (0.8 in.) from front to back. It is inferior to the urinary bladder and surrounds the prostatic urethra (Figure 26.9). The prostate slowly increases in size from birth to puberty, and then expands rapidly. The size at- tained by age 30 typically remains stable until about age 45, when further enlargement may occur.

renal columns

). Those portions of the renal cortex that extend between renal pyramids

Among the brush-border enzymes are four carbohydrate-digesting enzymes called

-dextrinase, maltase, sucrase, and lactase; protein-digesting enzymes called peptidases (aminopeptidase and dipeptidase); and two types of nucleotide-digesting enzymes, nucleosidases and phos- phatases. Also, as cells slough off into the lumen of the small intestine, they break apart and release enzymes that help digest nutrients in the chyme.

The lymphatic system has three primary functions:

. 1. Drains excess interstitial fluid. Lymphatic vessels drain ex- cess interstitial fluid from tissue spaces and return it to the blood. This function closely allies it with the cardiovascular system. In fact, without this function the maintenance of circulating blood volume would not be possible. 2. Transports dietary lipids. Lymphatic vessels transport the li- pids and lipid-soluble vitamins (A, D, E, and K), absorbed by the gastrointestinal tract, to the blood. 3. Carries out immune responses. Lymphatic tissue initiates highly specific responses directed against particular microbes or abnormal cells. With the assistance of macrophages, T and B cells recognize foreign cells, microbes, toxins, and cancer cells. These chemical substances that are recognized as foreign by the immune system are called antigens and provoke an im- mune response. T and B cells respond to antigens in several ways. B cells make up about 15-30 percent of the lymphocytes in the body. Most of the B cells differentiate into plasma cells that protect us against disease by producing antibodies, pro- teins that combine with and destroy specific foreign substances (antigens). Actually, the term antigen is so named because it is an antibody-generator. Some B cells become long-lived memory B cells, which can mount an even stronger immune response if the same antigen attacks the body at a later date. T cells, which make up 70-85 percent of the lymphocytes in the body, have several roles in the immune response. The four major types of T cells are helper T cells, cyototoxic T cells, reg- ulatory T cells, and memory T cells. Helper T cells cooperate with B cells to amplify antibody production by plasma cells. Fol- lowing activation by helper T cells, cytotoxic T cells destroy target cells on contact by causing them to rupture or by releasing cytotoxic (cell-killing) substances. Regulatory T cells (formerly called suppressor T cells) can turn off the immune response by sup- pressing T cells; this is important in combating an autoimmune disease (a disease caused by a reaction against the body's own cells). Regulatory T cells also protect beneficial intestinal bacte- ria, which aid digestion and produce some B vitamins and vita- min K. Memory T cells "remember" an antigen and mount a more vigorous response if the same antigen attacks the body in the future.

Mixing and propulsion

. Alternating contraction and relaxa- tion of smooth muscle in the walls of the GI tract mix food and secretions and move them toward the anus. This capabil- ity of the GI tract to mix and move material along its length is termed motility (moˉ -TIL-i-teˉ ).

functiosn of large intestine

. Haustral churning, peristalsis, and mass peristalsis drive the contents of the colon into the rectum. 2. Bacteria in the large intestine convert proteins to amino acids, break down amino acids, and produce some B vitamins and vitamin K. 3. Some water, ions, and vitamins are absorbed. 4. Feces are formed. 5. Defecation (emptying of the rectum) occurs.

Functionally, the respiratory system also consists of two parts.

1) The conducting zone consists of a series of interconnecting cavities and tubes both outside and within the lungs. These pas- sageways include the nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles; their function is to filter, warm, and moisten air and conduct it into the lungs. (2) The respiratory zone consists of tubes and tissues within the lungs where gas exchange occurs. These tubes and tissues include the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli, and are the main sites of gas exchange between air and blood.

The hepatic acinus is the smallest structural and functional unit of the liver. Its popularity and appeal are based on the fact that it provides a logical description and interpretation of

1) pat- terns of glycogen storage and release and (2) toxic effects, degen- eration, and regeneration relative to the proximity of the acinar zones to branches of the portal triad.

respiratory center, can be divided into two principal areas on the basis of location and function

1) the medullary respiratory center in the medulla oblongata and (2) the pontine respiratory group in the pons

secondary follicle, the theca differentiates into two layers:

1) the theca interna, a highly vascularized internal layer of cuboidal secretory cells that secrete estrogens, and (2) the theca externa, an outer layer of stromal cells and collagen fibers.

the interior structures of the nose have three functions:

1) warming, moistening, and filtering incoming air; (2) detecting olfactory (smell) stimuli; and (3) modifying speech vibrations as they pass through the large, hollow resonating chambers.

Extending from the alveolar air space to blood plasma, the respiratory membrane consists of four layers

1. A layer of type I and type II alveolar cells and associated alveolar macrophages that constitutes the alveolar wall 2. An epithelial basement membrane underlying the alveolar wall 3. A capillary basement membrane that is often fused to the epithelial basement membrane 4. The endothelial cells of the capillary wall Despite having several layers, the respiratory membrane is very thin—only 0.5 m thick, about one-sixteenth the diameter of a red blood cell. This thinness allows rapid diffusion of gases. It has been estimated that the lungs contain 300 million alveoli, providing an immense surface area of 70 m2 (750 ft2)—about the size of a handball court—for the exchange of gases.

The prostate secretes a milky, slightly acidic fluid (pH about 6.5) that contains several substances:

1. Citric acid in prostatic fluid is used by sperm for ATP production. 2. Several proteolytic enzymes, such as prostate-specific antigen (PSA), pepsinogen, lysozyme, amylase, and hyaluronidase, eventually break down the clotting proteins from the seminal vesicles. 3. The function of the acid phosphatase secreted by the prostate is unknown. 4. Seminalplasmin in prostatic fluid is an antibiotic that can de- stroy bacteria. Seminalplasmin may help decrease the number of naturally occurring bacteria in semen and in the lower fe- male reproductive tract. Secretions of the prostate enter the prostatic urethra through many prostatic ducts. Prostatic secretions make up about 25 per- cent of the volume of semen and contribute to sperm motility and viability.

trimesters.

1. During the rst trimester, the most critical stage of de- velopment, all of the major organ-systems begin to form. Because of the extensive, widespread activity, it is also the period when the developing organism is most vulnerable to the effects of drugs, radiation, and microbes. 2. The second trimester is characterized by the nearly complete development of organ systems. By the end of this stage, the fetus assumes distinctively human features. 3. The third trimester represents a period of rapid fetal growth in which the weight of the fetus doubles. During the early stages of this period, most of the organ systems become fully functional.

¥ Nephron Capillary Beds

1. Glomerulus Afferent arteriole glomerulus efferent arteriole Specialized for filtration Blood pressure is high because Afferent arterioles smaller in diameter than efferent arterioles Arterioles are high-resistance vessels ¥ Peritubular capillaries Low-pressure, porous capillaries adapted for absorption Arise from efferent arterioles Cling to adjacent renal tubules in cortex Empty into venules ¥ Vasa recta Long vessels parallel to long loops of Henle Arise from efferent arterioles of juxtamedullary nephrons Function in formation of concentrated urine

functions of stomach

1. Mixes saliva, food, and gastric juice to form chyme. 2. Serves as a reservoir for food before release into small intestine. 3. Secretes gastric juice, which contains HCl (kills bacteria and denatures proteins), pepsin (begins the digestion of proteins), intrinsic factor (aids absorption of vitamin B12), and gastric lipase (aids digestion of triglycerides). 4. Secretes gastrin into blood.

function of respiratory system

1. Provides for gas exchange— intake of O2 for delivery to body cells and removal of CO2 produced by body cells. 2. Helps regulate blood pH. 3. Contains receptors for the sense of smell, lters inspired air, produces sounds (phona- tion), and excretes small amounts of water and heat.

respiration three steps

1. Pulmonary ventilation. The first process, pulmonary ventilation (pulmo lung), or breathing, consists of inha- lation (inflow) and exhalation (outflow) of air and is the exchange of air between the atmosphere and the air spaces of the lungs. 2. External (pulmonary) respiration. This is the exchange of gases between the air spaces of the lungs and blood in pulmo- nary capillaries across the respiratory membrane. The blood gains O2 and loses CO2. 3. Internal (tissue) respiration. This is the exchange of gases between systemic capillary blood and tissue cells. The blood loses O2 and gains CO2.

Two "pumps" that aid the return of venous blood to the heart maintain the flow of lymph.

1. Skeletal muscle pump. The "milking action" of skeletal mus- cle contractions compresses lymphatic vessels (as well as veins) and forces lymph toward the junction of the internal jugular and subclavian veins (see Figure 14.4a). 2. Respiratory pump. Lymph flow is also maintained by pressure changes that occur during inhalation (breathing in). Lymph flows from the abdominal region, where the pressure is higher, toward the thoracic region, where it is lower. When the pressures reverse during exhalation (breathing out), the valves in lymphatic vessels prevent backflow of lymph. In addition, when a lymphatic vessel distends, the smooth muscle in its wall contracts, which helps move lymph from one segment of the vessel to the next.

Functions of urinary system

1. The kidneys regulate blood volume and composition; help regulate blood pressure, pH, and glucose levels; produce two hormones (calcitriol and erythropoietin); and excrete wastes in the urine. 2. The ureters transport urine from the kidneys to the urinary bladder. 3. The urinary bladder stores urine and expels it into the urethra. The urethra discharges urine from the body.

female reproductive system

1. The ovaries produce secondary oocytes and hormones, including progesterone and estro- gens (female sex hormones), inhibin, and relaxin. 2. The uterine tubes transport a secondary oocyte to the uterus and normally are the sites where fertilization occurs. 3. The uterus is the site of implantation of a fertilized ovum, development of the fetus during pregnancy, and labor. 4. The vagina receives the penis during sexual intercourse and is a passageway for childbirth. The mammary glands synthesize, secrete, and eject milk for nourishment of the newborn.

what they secrete

1. The seminal vesicles secrete alkaline, viscous uid that helps neutralize acid in the female reproductive tract, provides fructose for ATP production by sperm, contrib- utes to sperm motility and viability, and helps semen coagulate after ejaculation. 2. The prostate secretes a milky, slightly acidic uid that contains enzymes that break down clotting proteins from the seminal vesicles. 3. The bulbourethral glands secrete alkaline uid that neutralizes the acidic environment of the urethra and mucus that lubricates the lining of the urethra and tip of the penis during sexual intercourse.

male reproductive system functions

1. The testes produce sperm and the male sex hormone testosterone. 2. The ducts transport, store, and assist in maturation of sperm. 3. The accessory sex glands secrete most of the liquid portion of semen. 4. The penis contains the urethra, a passageway for ejaculation of semen and excretion of urine.

Before differentiation, all embryos have the following external structures

1. Urethral (urogenital) folds. These paired structures develop from mesoderm in the cloacal region (see Figure 25.13). 2. Urethral groove. An indentation between the urethral folds, which is the opening into the urogenital sinus. 3. Genitaltubercle.Aroundedelevationjustanteriortotheure- thral folds. ̄ 4. Labioscrotal swelling (la ̄-beˉ-oˉ-SKRO-tal). Paired, elevated structures lateral to the urethral folds.

Cells of the embryoblast also differentiate into two layers around 8 days after fertilization:

: a hypoblast (primitive endoderm) and epiblast (primitive ectoderm)

hydrocele

A collection of serous fluid in the cavity of the tunica vaginalis

myocardial infarction (MI)

A complete obstruction to blood flow in a coro- nary artery

primary follicles

A few primordial follicles start to grow, developing into primary follicles (Figure 26.14b). Each primary follicle consists of a pri- mary oocyte that is surrounded in a later stage of development by several layers of cuboidal and low-columnar cells called granu- losa cells (gran-u ̄-LO ̄ -sa). The outermost granulosa cells rest on a basement membrane. As the primary follicle grows, it forms a clear glycoprotein layer called the zona pellucida (pe-LOO- si-da) between the primary oocyte and the granulosa cells. In addition, stromal cells surrounding the basement membrane begin to form an organized layer called the theca folliculi (THE ̄ -ka fo-LIK-u ̄-l ̄ı).

renal cortex

A frontal section through the kidney reveals two distinct regions: a superficial, light red region

external elastic lamina

A less prominent network of elastic fibers, the external elastic lamina, forms the outer part of the tunica media and separates the tunica media from the outer tunica externa

a primary lymphatic nodule

A lymphatic nodule consisting chiefly of B cells

renal pelvis

A minor calyx receives filtrate from the papillary ducts of one renal papilla and delivers it to a major calyx. Once the filtrate enters the calyces it becomes urine because no further reabsorp- tion can occur. The reason for this is that the simple epithelium of the nephron and ducts becomes transitional epithelium in the calyces. From the major calyces, urine drains into a single large cavity called the renal pelvis (pelv- basin) and then out through the ureter to the urinary bladder.

stenosis

A narrowing of a heart valve opening that restricts blood flow

allergic (hypersensitive).

A person who is overly reactive to an antigen that is tolerated by most other people

retroflexion

A posterior tilting of the uterus, called retroflexion (ret-roˉ- FLEK-shun; retro- backward or behind), is a harmless variation of the normal position of the uterus. There is often no cause for the condition, but it may occur after childbirth or because of an ovarian cyst.

hymen

A thin fold of vascularized mucous membrane

muscularis mucosae

A thin layer of smooth muscle fibers called the muscularis mucosae (mu ̄ -KO ̄ -seˉ ) causes the mucous membrane of the stomach and small intestine to form many small folds, increas- ing the surface area for digestion and absorption. Movements of the muscularis mucosae ensure that all absorptive cells are fully exposed to the contents of the GI tract. The muscularis mucosae of the small intestine also surround the lacteal lymph vessels. Contractions of these smooth muscle cells help move the lymph along these vessels.

Migrating motility complex (MMC

A type of peristalsis consisting of waves of contraction and relaxation of circular and longitudinal smooth muscle fibers passing the length of the small intestine; moves chyme toward ileocecal sphincter

pluripotent stem cells

About 0.05-0.1 percent of red bone marrow cells

notochordal process

About 16 days after fertilization, mesodermal cells from the primitive node migrate toward the head end of the em- bryo and form a hollow tube of cells in the midline

implantation

About 6 days after fertilization, the blastocyst loosely attaches to the endometrium in a process

cortical nephrons

About 80-85 percent of the nephrons are cortical nephrons (KOR-ti-kal). Their re- nal corpuscles lie in the outer portion of the renal cortex, and they have short nephron loops that lie mainly in the cortex and penetrate only into the outer region of the renal medulla (Fig- ure 25.5a). The short nephron loops receive their blood supply from peritubular capillaries that arise from efferent arterioles.

Development of the Extraembryonic Coelom

About the twelfth day after fertilization, the extraembryonic mesoderm develops. These mesodermal cells are derived from the yolk sac and form a connective tissue (mesenchyme) around the amnion and yolk sac (Figure 4.6c). Soon, numerous large cav- ities develop in the extraembryonic mesoderm, which then fuse to form a single, even larger cavity called the extraembryonic coelom (SE ̄ -lom).

Glomerulus

Afferent arteriole glomerulus efferent arteriole Specialized for filtration Blood pressure is high because Afferent arterioles smaller in diameter than efferent arterioles Arterioles are high-resistance vessels

lymph

After interstitial fluid passes into lymphatic vessels

Events in the Ovaries

After ovulation, the mature follicle collapses, and the basement membrane between the granulosa cells and theca interna breaks down. Once a blood clot forms from minor bleeding of the rup- tured follicle, the follicle becomes the corpus hemorrhagicum (hem -oˉ -RAˉ J-i-kum; hemo- blood; rrhagic- bursting forth) (see Figure 26.13a). Theca interna cells mix with the granulosa cells as they all become transformed into corpus luteum cells under the influence of LH. Stimulated by LH, the corpus luteum secretes progesterone, estrogens, relaxin, and inhibin. The luteal cells also absorb the blood clot. Because of this activity, the postovulatory phase is also referred to as the luteal phase (LOO-teˉ-al) of the ovarian cycle. Later events in an ovary that has ovulated an oocyte depend on whether the oocyte is fertilized. If the oocyte is not fertilized, the corpus luteum has a life span of only 2 weeks. At the end of this time period, its secretory activity declines, and it degener- ates into a corpus albicans (see Figure 26.13a). As the levels of progesterone, estrogens, and inhibin decrease, release of GnRH, FSH, and LH rises due to loss of negative feedback suppression by the ovarian hormones. Follicular growth resumes, and a new ovarian cycle begins. If the secondary oocyte is fertilized and begins to divide, the corpus luteum persists past its normal 2-week life span. It is "res- cued" from degeneration by human chorionic gonadotropin (hCG) (koˉ-reˉ-ON-ik). This hormone is produced by the chorion of the embryo beginning about 8 days after fertilization. Like LH, hCG stimulates the secretory activity of the corpus luteum. The presence of hCG in maternal blood or urine is an indicator of pregnancy and is the hormone detected by home pregnancy tests.

Development of the Yolk Sac

Also on the eighth day after fertilization, cells of the hypoblast migrate and cover the inner surface of the blastocyst wall (Fig- ure 4.6a). The migrating cells form a thin membrane called the exocoelomic membrane (ek-so ̄-se ̄-LO ̄ -mik; exo- outside; -koilos space). Combined with the hypoblast, the exocoelomic membrane forms the wall of the yolk sac, the former blastocyst cavity (Figure 4.6b). As a result, the bilaminar embryonic disc is now positioned between the amniotic cavity and yolk sac. Since human embryos receive their nutrients from the en- dometrium, the yolk sac is relatively empty, small, and decreases in size as development progresses (see Figure 4.11a, inset). Nev- ertheless, the yolk sac has several important functions in humans. It supplies nutrients to the embryo during the second and third weeks of development, is the source of blood cells from the third through sixth weeks, contains the first cells (primordial germ cells) that will eventually migrate into the developing gonads and dif- ferentiate into gametes, forms part of the gut (gastrointestinal tract), and helps prevent drying out of the embryo.

sulci

Also on the surface of the heart are a series of grooves which contain coronary blood vessels and a variable amount of fat marks the external boundary between two chambers of the heart

azygos system

Although the brachiocephalic veins drain some portions of the thorax, most thoracic structures are drained by a network of veins the azygos, hemiazygos, and accessory hemiazygos veins

gastric lipase

Another en- zyme of the stomach Gastric lipase splits triglyc- erides (fats and oils) in fat molecules (such as those found in milk) into fatty acids and monoglycerides (a glyceride molecule attached to one fatty acid molecule). This enzyme has a limited role in the adult stomach.

external urethral orifice

Anterior to the vaginal orifice and posterior to the clitoristhe opening of the urethra to the exterior

Tubular reabsorption

As filtered fluid flows through the renal tubules and the collecting ducts, tubule cells reabsorb about 99 percent of the filtered water and many useful sol- utes. The water and solutes return to the blood as it flows through the peritubular capillaries and vasa recta. Note that the term reabsorption refers to the return of filtered water and solutes to the bloodstream. The term absorption, by contrast, means entry of new substances into the body, as occurs in the gastrointestinal tract.

Tubular secretion

As fluid flows through the renal tubules and collecting ducts, the renal tubule and duct cells secrete other materials, such as wastes, drugs, and excess ions, into the fluid. Notice that tubular secretion removes a substance from the blood.

amnion

As the amniotic cavity enlarges, a single layer of squamous cells forms a dome-like roof above the epiblast cells

amnion

As the amniotic cavity enlarges, a single layer of squamous cells forms a dome-like roof above the epiblast cells Initially, the amnion overlies only the bilaminar embry- onic disc. However, as the embryonic disc increases in size and begins to fold, the amnion eventually surrounds the entire embryo (see Figure 4.11a, inset), creating the amniotic cavity that becomes filled with amniotic fluid. Most amniotic fluid is initially derived from maternal blood. Later, the fetus con- tributes to the fluid by excreting urine into the amniotic cav- ity. Amniotic fluid serves as a shock absorber for the fetus, helps regulate fetal body temperature, helps prevent the fetus from drying out, and prevents adhesions between the skin of the fetus and surrounding tissues. The amnion usually ruptures just before birth; it and its fluid constitute the "bag of waters." Embryonic cells are normally sloughed off into amniotic fluid. They can be examined in a procedure called amniocentesis, which involves withdrawing some of the amniotic fluid that bathes the developing fetus and analyzing the fetal cells and dissolved substances

the guts

As they move toward the midline, the lateral folds incorporate the dor- sal part of the yolk sac into the embryo as the primitive gut, the forerunner of the gastrointestinal tract (Figure 4.12b). The primitive gut differentiates into an anterior foregut, an inter- mediate midgut, and a posterior hindgut

Truncus arteriosus

Ascending aorta and pulmonary trunk

arcuate arteries

At the bases of the renal pyramids, the interlo- bar arteries arch between the renal medulla-and cortex.

Development of the Cardiovascular System

At the beginning of the third week, angiogenesis (an-je ̄-o ̄-JEN- e-sis; angio- vessel; -genesis production), the formation of blood vessels, begins in the extraembryonic mesoderm of the yolk sac, connecting stalk, and chorion. This early development is neces- sary because there is insufficient yolk in the yolk sac and ovum to provide adequate nutrition for the rapidly developing embryo. Angiogenesis is initiated when mesodermal cells differentiate into hemangioblasts (he ̄ -MAN-je ̄ -o ̄ -blasts). These then develop into cells called angioblasts, which aggregate to form isolated masses of cells referred to as blood islands (see Figure 14.18). As the blood islands throughout the embryonic mesoderm grow they fuse together, forming an extensive system of blood vessels within the embryo. About 3 weeks after fertilization, blood cells and blood plasma begin to develop outside the embryo—in the walls of the yolk sac, allantois, and chorion—from hemangioblasts in blood vessels. These then develop into pluripotent stem cells that form blood cells. Blood formation begins within the embryo at about the fifth week in the liver and around the twelfth week in the spleen, red bone marrow, and thymus. The heart forms from splanchnic mesoderm in the head end of the embryo on day 18 or 19 after fertilization. This region of mesodermal cells is called the cardiogenic area (kar-de ̄-o ̄- JEN-ik; cardio- heart; -genic producing). In response to induction signals from the underlying endoderm, these mesodermal cells ultimately form a pair of endocardial tubes (see Figure 13.12b, c). The tubes then fuse to form a single primitive heart tube. By the end of the third week, the primitive heart tube bends on itself, becomes S-shaped, and begins to beat. It then joins blood vessels in other parts of the embryo, connecting stalk, chorion, and yolk sac to form a primitive cardiovascular system.

hepatic portal vein

At the same time the liver is receiving nutrient-rich but deoxygenated blood via the hepatic portal vein, it also is receiv- ing oxygenated blood via the hepatic artery, a branch of the celiac trunk. The oxygenated blood mixes with the deoxygenated blood in sinusoids. Eventually, blood leaves the sinusoids of the liver through the hepatic veins, which drain into the inferior vena cava.

anchoring filaments

Attached to the lymphatic capillaries are anchoring filaments, which contain elastic fibers. The anchor- ing filaments extend out from the lymphatic capillary, attaching (anchoring) lymphatic endothelial cells to surrounding tissues. When excess interstitial fluid accumulates and causes tissue swelling, the anchoring filaments are pulled, making the open- ings between cells even larger so that more fluid can flow into the lymphatic capillaries.

pleural cavity

Between the visceral and parietal pleurae is a small space

lobes of the lungs

Both lungs have an oblique fissure, which extends inferiorly and anteriorly; the right lung also has a horizontal fissure. The oblique fissure in the left lung separates the superior lobe from the inferior lobe. In the right lung, the superior part of the oblique fissure separates the superior lobe from the inferior lobe; the inferior part of the oblique fissure separates the inferior lobe from the middle lobe, which is bordered superiorly by the horizontal fissure.

mucous neck cells

Both mucous surface cells and mucous neck cells secrete mucus

cortical radiate

Branches of the arcuate arteries produce a series of cortical radiate (KOR- ti-kal RAˉ -deˉ -a ̄ t) or interlobular arteries. These arteries radiate out- ward and enter the renal cortex where they give off branches called afferent arterioles

arteries of uterus

Branches of the internal iliac artery called uterine arteries (Figure 26.19) supply blood to the uterus. Uterine arteries give off branches called arcuate arteries (AR-ku ̄-a ̄t shaped like a bow) that are arranged in a circular fashion in the myometrium. These arteries branch into radial arteries that penetrate deeply into the myometrium. Just before the branches enter the en- dometrium, they divide into two kinds of arterioles: Straight ar- terioles supply the stratum basalis with the materials needed to regenerate the stratum functionalis; spiral arterioles supply the stratum functionalis and change markedly during the menstrual cycle. Blood leaving the uterus is drained by the uterine veins into the internal iliac veins. The extensive blood supply of the uterus is essential to support regrowth of a new stratum func- tionalis after menstruation, implantation of a fertilized ovum, and development of the placenta.

Development of Somites

By about the seventeenth day after fertilization, the mesoderm adjacent to the notochord and neural tube forms paired longitu- dinal columns of paraxial mesodermal; para- near) (Figure 4.9b). The mesoderm lateral to the paraxial mesoderm forms paired cylindrical masses called intermediate mesoderm. The mesoderm lateral to the intermediate mesoderm consists of a pair of flattened sheets called lateral plate mesoderm. The paraxial mesoderm soon segments into a series of paired, cube- shaped structures called somites (SO ̄ -mi ̄ts little bodies) (Fig- ure 4.9c, d). By the end of the fifth week, 42-44 pairs of somites are present. The number of somites that develop over a given period can be correlated to the approximate age of the embryo.

ectoderm

Cells remaining in the epiblast All nervous tissue Epidermis of skin Hair follicles, arrector pili muscles, nails, epithelium of skin glands (sebaceous and sudoriferous), and mammary glands Lens, cornea, and internal eye muscles Internal and external ear Neuroepithelium of sense organs Epithelium of oral cavity, nasal cavity, paranasal sinuses, salivary glands, and anal canal Epithelium of pineal gland, pituitary gland, and adrenal medullae Melanocytes (pigment cells) Almost all skeletal and connective tissue components of the head Arachnoid mater

foreskin

Covering the glans in an uncircumcised penis is the loosely fitting

bulbourethral glands

Cowper's glands (KOW-pers), each about the size of a pea, lie in- ferior to the prostate on either side of the membranous urethra within the deep muscles of the perineum; their ducts open into the spongy urethra (Figure 26.9). During sexual arousal, the bulbo- urethral glands secrete an alkaline substance that protects the passing sperm by neutralizing acids from urine in the urethra. At the same time, they secrete mucus that lubricates the end of the penis and the lining of the urethra, thereby decreasing the number of sperm damaged during ejaculation. Some males re- lease a drop or two of this mucus upon sexual arousal and erec- tion. The fluid does not contain sperm cells.

Bulbourethral glands

Cowper's) - lubrication

micturition

Discharge of urine from the urinary bladder

Secretion

Each day, cells within the walls of the GI tract and accessory digestive organs secrete a total of about 7 liters of water, acid, buffers, and enzymes into the lumen (interior space) of the tract; this process is called secretion.

pleural membrane

Each lung is surrounded by a protective, double-layered serous mem- brane The two layers are continu- ous with one another where the bronchi enter the lung

Functions of the Urinary System

Elimination of the metabolic waste products and foreign substances • Fluid and electrolyte balance • Blood volume • Blood pressure (renin) • Erythropoiesis (erythropoietin)

Events in the Uterus

Estrogens liberated into the blood by growing ovarian follicles stimulate the repair of the endometrium; cells of the stratum ba- salis undergo mitosis and produce a new stratum functionalis. As the endometrium thickens, the short, straight endometrial glands develop, and the arterioles coil and lengthen as they penetrate the stratum functionalis. The thickness of the endometrium ap- proximately doubles, to about 4-10 mm. The preovulatory phase is also referred to as the proliferative phase (proˉ-LIF-er-a ̄-tiv) of the uterine cycle because the endometrium is proliferating.

Urethra

Exits urinary bladder in both sexes; in females, runs through perineal floor of pelvis to exit between labia minora; in males, passes through prostate, then perineal floor of pelvis, and then through penis (in male) to exit at tip Thin-walled tubes with three structural layers—inner mucosa (transitional, stratified columnar, and stratified squamous epithelium), thin middle layer of circular smooth muscle, and thin connective tissue exterior

vasa recta

Extending from some ef- ferent arterioles are long loop-shaped capillaries

raphe

Externally, the scrotum looks like a single pouch of skin separated into lateral portions by a median ridge

Hepatic lobule

For years, anatomists described the hepatic lobule as the functional unit of the liver. According to this model, each hepatic lobule is shaped like a hexagon (six-sided structure) (Figure 24.14d, left). At its center is the central vein and radiating out from it are rows of hepatocytes and hepatic sinusoids. Located at three corners of the hexagon is a portal triad. This model is based on a description of the liver of adult pigs. In the human liver it is difficult to find such well-defined hepatic lobules surrounded by thick layers of connective tissue.

uvula

Hanging from the free border of the soft palate is a finger-like muscular structure

pancreatic duct

In most people, the pancreatic duct joins the common bile duct from the liver and gallbladder and enters the duodenum as a dilated common duct called the hepatopan- creatic ampulla

The hepatocytes, bile duct system, and hepatic sinusoids can be organized into anatomical and functional units in three dif- ferent ways:

Hepatic lobule Hepatic sinusoids Portal lobule Hepatic acinus

Hepatocytes

Hepatocytes are the major functional cells of the liver and perform a wide array of metabolic, secretory, and endocrine functions. These are specialized epithelial cells with 5 to 12 sides that make up about 80 percent of the volume of the liver. Hepatocytes are arranged in rows called hepatic laminae (LAM-i-neˉ). The hepatic laminae are plates of hepatocytes one cell thick bordered on either side by endothelial-lined vascular spac- es called hepatic sinusoids. The hepatic laminae are highly branched, irregular structures. Grooves in the cell mem- branes between neighboring hepatocytes provide spaces for canaliculi (described next), into which the hepatocytes secrete bile. Bile, a yellow, brownish, or olive-green liquid secreted by hepatocytes, serves as both an excretory product and a digestive secretion.

Gallbladder

Hepatocytes continuously secrete 800-1000 mL (about 1 qt) of bile per day. Bile salts, which are sodium salts and potassium salts of bile acids (mostly cholic acid and chenodeoxycholic acid), play roles in (1) emulsification (eˉ -mul-si-fi-KAˉ -shun), the breakdown of large lipid globules into a suspension of droplets about 1 m in diameter, and (2) the absorption of digested lipids. Between meals, bile flows into the gallbladder for storage be- cause the sphincter of the hepatopancreatic ampulla or sphinc- ter of Oddi (OD-eˉ) (see Figure 24.12b) closes off the entrance to the duodenum. The sphincter surrounds the hepatopancreatic ampulla. After a meal, several neural and hormonal stimuli pro- mote the production and release of bile. Parasympathetic impulses along the vagus (X) nerve fibers can stimulate the liver to increase bile production to more than twice the baseline rate. Fatty acids and amino acids in chyme entering the duodenum stimulate some duodenal enteroendocrine cells to secrete the hormone chole- cystokinin (CCK) into the blood. CCK causes contraction of the walls of the gallbladder, which squeezes stored bile out of the gall- bladder into the cystic duct and through the common bile duct. CCK also causes relaxation of the sphincter of the hepatopancre- atic ampulla, which allows bile to flow into the duodenum. used for ATP production or converted to carbohydrates or fats. The resulting toxic ammonia (NH3) is then converted into the much less toxic urea, which is excreted in urine. Hepatocytes also synthesize most plasma proteins, such as alpha and beta globulins, albumin, prothrombin, and fibrinogen.

urethra males

In males, the urethra (u ̄-RE ̄ -thra) is the shared terminal duct of the reproductive and urinary systems; it serves as a passageway for both semen and urine. About 20 cm (8 in.) long, it passes through the prostate, the deep muscles of the perineum, and the penis, and is subdivided into three parts (see Figures 26.1a and 26.9).

Conditions of the kidney

In a condition called unilateral renal agenesis (a ̄-JEN-e-sis; a- without; genesis production; unilateral one side), only one kidney develops (usually the right) due to the absence of a ureteric bud. The condition occurs once in every 1000 newborn infants and usually affects males more than females. Other kidney abnor- malities that occur during development are malrotated kidneys (the hilum faces anteriorly, posteriorly, or laterally instead of me- dially); ectopic kidney (abnormal position of one or both kidneys, usually inferior); and horseshoe kidney (the fusion of the two kidneys, usually inferiorly, into a single U-shaped kidney). Urinary tract infections are more common among the elderly, as are polyuria (pol -eˉ-U ̄ -reˉ-a; poly- too much) (excessive urine production), nocturia (excessive urination at night), increased frequency of urination, dysuria (dis-U ̄ -reˉ-a; dys painful; uria urine) (pain- ful urination), urinary retention or incontinence, and hematuria (blood in the urine).

baroreceptors

In addition to all of the previously mentioned factors, receptors in the musculature of the bronchi and bronchioles throughout the lungs themselves can also modify breathing. Within these air passageways are stretch-sensitive receptors

G cell

In addition, gastric glands include a type of entero- endocrine cell, the G cell, which is located mainly in the pyloric antrum and secretes the hormone gastrin into the bloodstream.

DHT

In male embryos, some testosterone is converted to a second an- drogen stimulates development of the urethra, prostate, and external genitals

Hepatic acinus

In recent years, the preferred structural and functional unit of the liver has become the hepatic acinus (AS-i-nus). Each hepatic acinus is an approximately oval mass that includes portions of two neighboring hepatic lobules. The short axis of the hepatic acinus is defined by branches of the portal triad--branches of the hepatic artery, vein, and bile ducts--that run along the border of the he- patic lobules. The long axis of the acinus is defined by two imaginary curved lines, which connect the two central veins closest to the short axis (Figure 24.14d, right). Hepatocytes in the hepatic acinus are arranged in three zones around the short axis, with no sharp boundaries between them (Fig- ure 24.14e). Cells in zone 1 are closest to the branches of the portal triad and the first to receive incoming oxygen, nutrients, and toxins from incoming blood. These cells are the first ones to take up glucose, store it as glycogen after a meal, and break down glycogen to glucose during fasting. They are also the first to show morphological changes fol- lowing bile duct obstruction or exposure to toxic substances. Zone 1 cells are the last ones to die if circulation is impaired and the first ones to regenerate. Cells in zone 3 are farthest from branches of the portal triad and are the last to show the effects of bile obstruction or exposure to toxins, the last to regenerate, and the first ones to show the effects of impaired circulation. Zone 3 cells also are the first to show evidence of fat accumulation. Cells in zone 2 have structural and functional characteristics intermediate between the cells in zones 1 and 3.

Glomerular filtration

In the first step of urine produc- tion, water and most solutes in blood plasma move across the wall of capillaries in the glomeruli where they are fil- tered and move into the glomerular capsule and then into the renal tubule.

trigone

In the floor of the urinary bladder is a small triangular area

lacteals

In the small intestine, specialized lymphatic capillaries

interstitial cells

In the spaces between adjacent seminiferous tubules are clus- ters of cells These cells secrete testosterone, the most important androgen.

interstitial cells or Leydig cells

In the spaces between adjacent seminiferous tubules are clus- tersofcells

Development of the Intraembryonic Coelom

In the third week of development, small spaces appear in the lat- eral plate mesoderm. These spaces soon merge to form a larger cavity called the intraembryonic coelom (SE ̄-lo ̄m cavity). This cavity splits the lateral plate mesoderm into two parts called the splanchnic mesoderm and somatic mesoderm (Figure 4.9d). Splanchnic mesoderm (SPLANGK-nik visceral), which is ad- jacent to the endoderm and yolk sac, forms the heart and the visceral layer of the serous pericardium, blood vessels, the smooth muscle and connective tissues of the respiratory and digestive or- gans, and the visceral layer of the serous membrane of the pleu- rae and peritoneum. Somatic mesoderm (so ̄-MAT-ik; soma- body), which is adjacent to the ectoderm and amnion, gives rise to the bones, ligaments, blood vessels, and connective tissue of the limbs and the parietal layer of the serous membrane of the pericardium, pleurae, and peritoneum. During the second month of development, the intraembryonic coelom is partitioned into the pericardial, pleural, and peritoneal cavities.

descending limb of the nephron loop

It begins in the renal cortex and ex- tends downward into the renal medulla

fimbriae

It ends in a fringe of fingerlike projections called fimbriae (FIM-breˉ -eˉ fringe), one of which is attached to the lateral end of the ovary.

lower esophageal sphincter (LES)

It is also called the cardiac sphincter because of its proximity to the heart. (A physiological sphincter is a section of a tubular structure, in this case the esophagus, which functions like a sphincter even though no sphincter muscle is actually present.) The lower esophageal sphincter relaxes during swallowing and thus allows the bolus to pass from the esophagus into the stomach.

During the fourth week of development, the embryo under- goes dramatic changes in shape and nearly triples its size.

It is essentially converted from a flat, two-dimensional trilaminar embryonic disc to a three-dimensional cylinder, via a process called embryonic folding (Figure 4.12). The cylinder consists of endoderm in the center (gut lining), ectoderm primarily on the outside (epidermis), and mesoderm in between. The cylin- der does contain some internal ectoderm from neurulation (the nervous system and most of the structures of the head). The main force responsible for embryonic folding is the different rates of growth of various parts of the embryo, especially the rapid longitudinal growth of the nervous system (neural tube). Folding in the median plane produces a head fold and a tail fold, while folding in the horizontal plane results in the two lateral folds. As a result of the folding, the embryo curves into a C-shape.

ascending limb of the nephron loop

It then makes that hairpin turn and returns to the renal cortex where it terminates at the distal convoluted tubule

Parts of the Urinary System

Kidneys Ureters Bladder Urethra

mesangial cells

Located among the glomerular capillaries and in the cleft between afferent and efferent arterioles

Urinary bladder

Located in pelvic cavity anterior to sacrum and rectum in males and sacrum, rectum, and vagina in females and posterior to the pubis in both sexes; in males, superior surface is covered with parietal peritoneum; in females, uterus covers superior aspect Hollow, distensible, muscular organ with variable shape depending on amount of urine; three basic layers— inner mucosa of transitional epithelium, middle smooth muscle coat called detrusor muscle, and outer adventitia or serosa over superior aspect in males

Vasa recta

Long vessels parallel to long loops of Henle Arise from efferent arterioles of juxtamedullary nephrons Function in formation of concentrated urine

Peritubular capillaries

Low-pressure, porous capillaries adapted for absorption Arise from efferent arterioles Cling to adjacent renal tubules in cortex Empty into venules

lh

Luteinizing hormone (LH, also known as lutropin and sometimes lutrophin[1]) is a hormone produced by gonadotropic cells in the anterior pituitary gland. In females, an acute rise of LH ("LH surge") triggers ovulation[2] and development of the corpus luteum. In males, where LH had also been called interstitial cell-stimulating hormone (ICSH),[3] it stimulates Leydig cell production of testosterone.[2] It acts synergistically with FSH

mucosa- associated lymphatic tissue (MALT).

Lymphatic nodules are egg-shaped masses of lymphatic tissue; unlike lymph nodes, they are not surrounded by a capsule. Be- cause they are scattered throughout the lamina propria (con- nective tissue) of mucous membranes lining the gastrointestinal, urinary, and reproductive tracts, and the respiratory airways, lymphatic nodules in these areas

Events in the Uterus

Menstrual flow from the uterus consists of 50-150 mL of blood, tissue fluid, mucus, and epithelial cells shed from the en- dometrium. This discharge occurs because the declining level of The length of the female reproductive cycle typically is 24-36 days; the preovulatory phase is more variable in length than the other phases. ovarian progesterone and estrogens stimulates release of prosta- glandins that cause the uterine spiral arterioles to constrict. As a result, the cells they supply become oxygen-deprived and start to die. Eventually, the entire stratum functionalis sloughs off. At this time the endometrium is very thin, about 2-5 mm, because only the stratum basalis remains. The menstrual flow passes from the uterine cavity through the cervix and vagina to the exterior.

micturition reflex

Micturition occurs via a combination of invol- untary and voluntary muscle contractions. When the volume of urine in the urinary bladder exceeds 200-400 mL, pressure within the urinary bladder increases considerably, and stretch receptors in its wall transmit nerve impulses into the spinal cord. These im- pulses propagate to the micturition center in sacral spinal cord segments S2 and S3 and trigger a spinal reflex parasympathetic impulses from the micturition center propagate to the urinary bladder wall and inter- nal urethral sphincter. The nerve impulses cause contraction of the detrusor muscle and relaxation of the internal urethral sphincter muscle. Simultaneously, the micturition center inhibits somatic motor neurons that innervate skeletal muscle in the external ure- thral sphincter. Upon contraction of the urinary bladder wall and relaxation of the sphincters, urination takes place. Urinary bladder filling causes a sensation of fullness that initiates a conscious desire to urinate before the micturition reflex actually occurs.

Formation and Flow of Lymph

Most components of blood plasma, such as nutrients, gases, and hormones, filter freely through the capillary walls to form inter- stitial fluid. More fluid filters out of blood capillaries, however, than returns to them by reabsorption. The excess filtered fluid— about 3 liters per day—drains into lymphatic vessels and becomes lymph. Because most blood plasma proteins are too large to leave blood vessels, interstitial fluid contains only a small amount of protein. Proteins that do leave blood plasma cannot return to the blood directly by diffusion because the concentration gradient (high level of proteins inside blood capillaries, low level outside) opposes such movement. The proteins can, however, move read- ily through the more permeable lymphatic capillaries into lymph. Thus, an important function of lymphatic vessels is to return lost blood plasma proteins and plasma to the bloodstream. Without this return of lymph (plasma lost from the blood) to the blood, the blood volume would drop precipitously and the cardiovascular system would cease to function. Therefore, the lymphatic vessels are a key part of the cardiovascular pathways in the body.

the small intestine.

Most digestion and absorption of nutrients occur in a long tube called the small intestine. Because of this, its structure is specially adapted for this function. Its length alone provides a large surface area for digestion and absorption, and that area is further increased by circular folds, villi, and microvilli. The small intestine begins at the pyloric sphincter of the stomach, coils through the central and inferior part of the abdominal cavity, and eventually opens into the large intestine. It averages 2.5 cm (1 in.) in diameter; its length isabout3m(10ft)inalivingpersonandabout6.5m(21ft)ina cadaver due to the loss of smooth muscle tone after death.

secondary lymphatic nodules

Most lymphatic nodules in the outer cortex

nerve supply to kidneys

Most renal nerves originate in the celiac and aorticorenal ganglia as postganglionic neurons of the sympathetic division of the au- tonomic nervous system (see Figure 19.3a) and pass through the renal plexus into the kidneys along with the renal arteries. Because renal nerves are part of the sympathetic division of the autonomic nervous system (see Section 19.3), most are vasomotor nerves that regulate the flow of blood through the kidney by causing vasodilation or vasoconstriction of renal arterioles.

renal hilum

Near the center of the concave border is an indentation through which the ureter emerges from the kidney along with blood vessels, lymphatic vessels, and nerves.

anteflexion

Normally, the body of the uterus projects anteriorly and su- periorly over the urinary bladder in a position called anteflexion (an -teˉ-FLEK-shun; ante before). The cervix projects inferiorly and posteriorly and enters the anterior wall of the vagina at nearly a right angle

paraurethral glands

On either side of the external urethral orifice are the openings of the ducts of the

greater vestibular glands

On either side of the vaginal orifice itself are the greater vestibular glands or Bar- tholin's glands (BAR-toˉ-lins) (see Figure 26.22), which open by ducts into a groove between the hymen and labia minora. They produce a small quantity of mucus during sexual arousal and intercourse that adds to cervical mucus and provides lubrication. The greater vestibular glands are homologous to the bulbourethral glands in males.

auricle

On the anterior surface of each atrium is a wrinkled pouchlike structure

Development of Sinusoids

On the ninth day after fertilization, the blastocyst becomes com- pletely embedded in the endometrium. As the syncytiotrophob- last expands into the endometrium and around the yolk sac, small spaces called lacunae (la-KOO-ne ̄ little lakes) develop within it (Figure 4.6b). By the twelfth day of development, the lacunae fuse to form larger, interconnecting spaces called lacunar networks (Fig- ure 4.6c). Endometrial capillaries (microscopic maternal blood vessels) around the developing embryo expand and are referred to as maternal sinusoids (SI ̄ -ne-soids). As the syncytiotrophoblast erodes some of the sinusoids and endometrial glands, maternal blood and glandular secretions enter the lacunar networks, which serve as both a rich source of materials for embryonic nutrition and a disposal site for the embryo's wastes.

mesoderm

Other migrating cells remain between the epiblast and newly formed endoderm All skeletal and cardiac muscle tissue and most smooth muscle tissue Most cartilage, bone, and other connective tissues Blood, red bone marrow, and lymphatic tissue Blood vessels and lymphatic vessels Dermis of skin Fibrous tunic and vascular tunic of eye Mesothelium of thoracic, abdominal, and pelvic cavities Kidneys and ureters Adrenal cortex Gonads and genital ducts (except germ cells) Dura mater

Primitive atrium

Part of right atrium (anterior wall), right auricle, part of left atrium (anterior wall), and left auricle

Kidneys

Posterior abdomen between last thoracic and third lumbar vertebrae posterior to peritoneum (retroperitoneal); lie against eleventh and twelfth ribs \ Solid, reddish bean-shaped organs; internal structure consists of three tubular systems—arteries, veins, and urinary tubes—that form an intimate interface

Ureters

Posterior to the peritoneum (retroperitoneal); descend from kidney to urinary bladder along anterior surface of psoas major muscle and cross back of pelvis to reach inferoposterior surface of urinary bladder anterior to the sacrum Thick, muscular walled tubes with three structural layers—mucosa of transitional epithelium, muscularis with circular and longitudinal layers of smooth muscle, and adventitia of areolar connective tissue

Ducts of the Testis

Pressure generated by the fluid secreted by sustentacular cells pushes sperm and fluid along the lumen of seminiferous tubules and then into a series of very short ducts called straight tubules. The straight tubules lead to a network of ducts in the testis called the rete testis (Reˉ-teˉ network) (see Figure 26.3a). From the rete testis, sperm move into a series of coiled efferent ducts (EF-e-rent) in the epididymis that empty into a single tube called the ductus epididymis.

Events in the Uterus

Progesterone and estrogens produced by the corpus luteum pro- mote growth and coiling of the endometrial glands, vasculariza- tion of the superficial endometrium, and thickening of the en- dometrium to 12-18 mm (0.48-0.72 in.). Because of the secretory activity of the endometrial glands, which begin to secrete glyco- gen, this period is called the secretory phase of the uterine cycle. These preparatory changes peak about one week after ovulation, at the time a fertilized ovum might arrive in the uterus. If ferti- lization does not occur, the levels of progesterone and estrogens decline due to degeneration of the corpus luteum. Withdrawal of progesterone and estrogens causes menstruation.

Parietal cells

Secrete hydrochloric acid Kills microbes in food; denatures proteins; converts pepsinogen into pepsin Secrete intrinsic factor Needed for absorption of vitamin B12, which is used in red blood cell formation (erythropoiesis)

Chief cells

Secrete pepsinogen Pepsin, the activated form, breaks down proteins into peptides Secrete gastric lipase Splits triglycerides into fatty acids and monoglycerides

gastric pits

Several gastric glands open into the bottom of narrow channels

Functions of the Stomach

Several minutes after food enters the stomach, waves of peristalsis pass over the stomach every 15 to 25 seconds. Few peristaltic waves are observed in the fundus, which primarily has a storage function. Instead, most waves begin at the body of the stomach and intensify as they reach the antrum. Each peristaltic wave moves gastric con- tents from the body of the stomach down into the antrum, a proc- ess known as propulsion. The pyloric sphincter normally remains almost, but not completely, closed. Because most food particles in the stomach initially are too large to fit through the narrow py- loric sphincter, they are forced back into the body of the stomach, a process referred to as retropulsion. Another round of propulsion then occurs, moving the food particles back down into the antrum. If the food particles are still too large to pass through the pyloric sphincter, retropulsion occurs again as the particles are squeezed back into the body of the stomach. Then yet another round of pro- pulsion occurs, and the cycle continues to repeat. The net result of these movements is that gastric contents are mixed with gastric juice, eventually becoming reduced to a soupy liquid called chyme (KIˉM juice). Once the food particles in chyme are small enough, they can pass through the pyloric sphincter, a phenomenon known as gastric emptying. Gastric empyting is a slow process: only about 3 mL of chyme move through the pyloric sphincter at this time. Within 2-4 hours after eating a meal, the stomach has emp- tied its contents into the duodenum. Foods rich in carbohydrate spend the least time in the stomach; high-protein foods remain somewhat longer; and emptying is slowest after a fat-laden meal containing large amounts of triglycerides. The stomach wall is impermeable to the passage of most mate- rials into the blood; most substances are not absorbed until they reach the small intestine. However, the stomach does participate in the absorption of some water, electrolytes, certain drugs (espe- cially aspirin), and alcohol.

Events in the Ovaries

Some of the secondary follicles in the ovaries begin to secrete es- trogens and inhibin. By about day 6, a single secondary follicle in one of the two ovaries has outgrown all the others to become the dominant follicle. Estrogens and inhibin secreted by the domi- nant follicle decrease the secretion of FSH, which causes other, less well-developed follicles to stop growing and undergo atresia. Fraternal (nonidentical) twins or triplets result when two or three secondary follicles become codominant and later are ovulated and fertilized at about the same time. Normally, the one dominant secondary follicle becomes the mature (graafian) follicle, which continues to enlarge until it is more than 20 mm in diameter and ready for ovulation (see Figure 26.13a). This follicle forms a blisterlike bulge due to the swelling antrum on the surface of the ovary. During the final maturation process, the mature follicle continues to increase its production of estrogens. With reference to the ovarian cycle, the menstrual and pre- ovulatory phases together are termed the follicular phase (fo- LIK-u ̄-lar) because ovarian follicles are growing and developing.

morula

Successive cleavages eventually become more rapid and produce a solid sphere of cells

major duodenal papilla

The ampulla opens onto an elevation of the duodenal mucosa, the major duodenal papilla, that lies about 10 cm (4 in.) inferior to the pyloric sphincter of the stomach.

A series of ligaments holds them in position

The broad ligament of the uterus, which is a fold of the perito- neum, attaches to the ovaries by a subset of this peritoneal fold called the mesovarium (mez -oˉ -VA-reˉ -um). The ovarian liga- ment anchors the ovaries to the uterus, and the suspensory liga- ment attaches them to the pelvic wall. Each ovary contains a hilum (HI ̄-lum), the point of entrance and exit for blood vessels and nerves along which the mesovarium is attached (see Figure 26.13).

efferent arteriole

The capillar- ies of the glomerulus then reunite to form an efferent arteriole (EF-er-ent; ef- out), which has a smaller diameter than the af- ferent arteriole. The efferent arteriole carries blood out of the glomerulus toward a second capillary plexus

germinal center

The center of a secondary lymphatic nodule contains a region of light-staining cells

accessory sex glands

The ducts of the male reproductive system store and transport sperm cells, but the accessory sex glands secrete most of the liquid portion of semen. The accessory sex glands include the seminal vesicles, the prostate, and the bulbourethral glands.

spermatids

The chromo- somes line up in single file along the metaphase plate, and the two chromatids of each chromosome separate. The four haploid cells resulting from meiosis II

decidua 3 layers

The decidua basalis is the portion of the endometrium beneath the implanting embryo; it provides large amounts of glycogen and lipids for the developing embryo and fetus and later becomes the maternal part of the pla- centa. The decidua capsularis is the portion of the endometrium that will cover the embryo after it implants in the endometrium. The decidua parietalis (par-ri ̄-e-TAL-is) is the remaining mod- ified endometrium that lines the noninvolved areas of the rest of the uterus.

renal capsule

The deep layer, the renal capsule, is a smooth, transparent sheet of dense irregular connective tissue that is continuous with the outer coat of the ureter. It serves as a barrier against trauma and helps maintain the shape of the kidney.

mucosa

The deepest coat, or mucosa, is a mucous membrane with transitional epithelium (see Table 3.1) and an underlying lamina propria of areolar connective tissue with considerable collagen, elastic fibers, and lymphatic tissue.

Three coats make up the wall of the urinary bladder

The deepest is the mucosa, a mucous membrane composed of transitional epithelium and an underlying lamina propria similar to that of the ureters. The transitional epithelium permits stretching. Rugae (folds in the mucosa) are also present. Surrounding the mucosa is the intermediate muscularis, also called the detrusor musclewhich consists of three layers of smooth muscle fibers: the in- ner longitudinal, middle circular, and outer longitudinal layers. Around the opening to the urethra the circular fibers form an internal urethral sphincter (see Figure 25.9a); inferior to it is the external urethral sphincter, which is composed of skeletal muscle. The most superficial coat of the urinary bladder on the posterior and inferior surfaces is the adventitia, a layer of areolar connective tissue that is continuous with that of the ureters. Over the superior surface of the urinary bladder is the serosa, a layer of peritoneum.

ampulla

The dilated terminal por- tion of the ductus deferens

zygote

The dip- loid fertilized ovum is now called and begins to undergo cell divisions while moving toward the uterus. It arrives in the uterus 6 to 7 days after ovulation. Unfertilized secondary oocytes disintegrate.

hypoxia

The direct stimulus for the production of red blood cells

glans penis

The distal end of the corpus spongiosum penis is a slightly enlarged, acorn-shaped region its margin is the corona

external urethral orifice

The distal urethra enlarges within the glans penis and forms a terminal slitlike opening

Absorption

The entrance of ingested and secreted fluids, ions, and the products of digestion into the epithelial cells lining the lumen of the GI tract is called absorption. The absorbed substances pass into the blood or lymph and circulate to cells throughout the body.

respiratory membrane

The exchange of O2 and CO2 between the air spaces in the lungs and the blood takes place by diffusion across the alveo- lar and capillary walls, which together form the

infundibulum

The funnel-shaped portion of each uterine tubeone of which is attached to the lateral end of the ovary.

chorion

The extraembryonic mesoderm and the two layers of the tro- phoblast (the cytotrophoblast and the syncytiotrophoblast) to- gether form the chorion (KOR-e ̄-on membrane) (Figure 4.6c). The chorion surrounds the embryo and, later, the fetus (see Figure 4.11a, inset). Eventually the chorion becomes the prin- cipal embryonic part of the placenta, the structure for exchange of materials between mother and fetus. The chorion also pro- tects the embryo and fetus from the immune responses of the mother in two ways: (1) It secretes proteins that block antibody production by the mother; and (2) it promotes the production of T lymphocytes that suppress the normal immune response in the uterus. Finally, the chorion produces human chorionic gonado- tropin (hCG), an important hormone of pregnancy.

Development of the Chorion

The extraembryonic mesoderm and the two layers of the tro- phoblast (the cytotrophoblast and the syncytiotrophoblast) to- gether form the chorion (KOR-e ̄-on membrane) (Figure 4.6c). The chorion surrounds the embryo and, later, the fetus (see Figure 4.11a, inset). Eventually the chorion becomes the prin- cipal embryonic part of the placenta, the structure for exchange of materials between mother and fetus. The chorion also pro- tects the embryo and fetus from the immune responses of the mother in two ways: (1) It secretes proteins that block antibody production by the mother; and (2) it promotes the production of T lymphocytes that suppress the normal immune response in the uterus. Finally, the chorion produces human chorionic gonado- tropin (hCG), an important hormone of pregnancy. The inner layer of the chorion eventually fuses with the am- nion. With the development of the chorion, the extraembryonic coelom is now referred to as the chorionic cavity. By the end of the second week of development, the bilaminar embryonic disc is connected to the trophoblast by a band of extraembryonic meso- derm called the connecting (body) stalk (see Figure 4.7, inset), the future umbilical cord.

, gastrula- tion

The first major event of the third week of development, gastrula- tion (gas-troo-LA ̄ -shun), occurs about 15 days after fertilization. In this process, the bilaminar (two-layered) embryonic disc, con- sisting of epiblast and hypoblast, is transformed into a trilaminar (three-layered) embryonic disc consisting of three primary germ layers: the ectoderm, mesoderm, and endoderm.

pyloric part

The first region, the pyloric antrum, con- nects to the body of the stomach. The next region, the pyloric canal, leads to the third region, the pylorus (p ̄ı-LOR-us; pyl- gate; orus guard), which in turn connects to the duodenum. When the stomach is empty, the mucosa lies in large folds, called rugae (ROO-geˉ wrinkles), which can be seen with the unaided eye. The pylorus communicates with the duodenum of the small intestine via a smooth muscle sphincter called the pyloric sphinc- ter (valve). The concave medial border of the stomach is called the lesser curvature, and the convex lateral border is called the greater curvature.

the glomeru- lar filtrate

The fluid that enters the capsular space

oogenesis

The formation of gametes in the ovariesUnlike spermatogenesis, which begins in males at puberty, oogenesis begins in females before they are born. As in spermatogenesis, meiosis (see Section 2.5) takes place and the resulting germ cells undergo maturation.

Neutrophil

The granules of a neutrophil are smaller, evenly distributed, and pale lilac in color Because the granules do not strongly attract either the acidic (red) or basic (blue) stain, these WBCs are neutrophilic ( neutral loving). The nucleus has two to five lobes, connected by very thin strands of nuclear material. As the cells age, the number of nuclear lobes increases. Because older neutrophils thus have several differently shaped nuclear lobes, they are often called polymorphonuclear leukocytes (PMNs), or "polys."

renal sinus

The hilum expands into a cavity within the kidney called the renal sinus, which contains part of the renal pelvis, the calyces,

labial frenulum

The inner surface of each lip is attached to its corresponding gum by a midline fold of mucous membrane

uterine cavity

The interior of the body of the uterus

intermediate (mem- branous) urethra

The intermediate urethra is about 1 cm (0.5 in.) in length. As this duct passes through the cor- pus spongiosum of the penis, it is known as the spongy (penile) urethra

renal medulla

The kidneys are surrounded by a renal capsule, adipose capsule, and renal fascia. or bark) and a deep, darker red-brown regionThe renal medulla consists of several cone-shaped renal pyramids. The base (wider end) of each pyramid faces the renal cortex, and its apex (narrower end), called a renal papilla, points toward the renal hilum. The smooth-textured renal cortex extends from the renal capsule to the bases of the renal pyramids and into the spaces between them.

adventitia

The most superficial layer of the trachea, the adventitia, consists of areolar connective tissue that joins the trachea to surrounding tissues.

systemic pump

The left pump, comprised of the left atrium and left ventricle, is the stronger circulates oxygen- ated blood to all the systems of the body.

lymph trunks

The lumbar trunks drain lymph from the free lower limbs, the wall and viscera of the pelvis, the kidneys, the adrenal glands, and the abdominal wall. The intestinal trunk drains lymph from the stomach, intes- tines, pancreas, spleen, and part of the liver. The bronchomedi- astinal trunks (brong-ko ̄-me ̄ -de ̄-as-TI ̄-nal) drain lymph from the thoracic wall, lung, and heart. The subclavian trunks drain the free upper limbs. The jugular trunks drain the head and neck.

pericardium

The membrane that surrounds and protects the heart

adipose capsule

The middle layer, the ad- ipose capsule, is a mass of fatty tissue surrounding the renal cap- sule. It also protects the kidney from trauma and holds it firmly in place within the abdominal cavity.

nostrils

The openings into the external nose are the external nares (NAˉ -reˉ z; singular is naris) or nostrils, which lead into cavities about the size of a finger tip called the nasal vestibules.

gastric glands

The mucosa con- tains a lamina propria (areolar connective tissue) and a muscu- laris mucosae (smooth muscle). Inward folds of epithelial cells extend down into the lamina propria, where they form columns of secretory cells

Lymphocyte

The nucleus of a lymphocyte stains dark and is round or slightly indented (Figure 12.5d). The cytoplasm stains sky blue and forms a rim around the nucleus. The larger the cell, the more cytoplasm is vis- ible. Lymphocytes are classified by cell diameter as large lymphocytes (10-14 m) or small lymphocytes (6-9 m). Although the functional significance of the size difference between small and large lymphocytes is unclear, the dis- tinction is still clinically useful because an increase in the number of large lymphocytes has diagnostic significance in acute viral infections and in some immunodeficiency diseases.

epithelium in nose

The olfactory receptor cells, supporting cells, and basal cells lie in the olfactory region, the membrane lining the superior nasal conchae, and adjacent nasal septum. This region is called the olfac- tory epithelium (see Figure 21.1). It contains cilia but no goblet cells. Inferior to the olfactory epithelium, the mucous membrane contains capillaries and pseudostratified ciliated columnar epithe- lium with many goblet cells; this epithelium in the respiratory re- gion is called the respiratory epithelium. As inhaled air whirls around the conchae and meatuses, it is warmed by blood circulat- ing in the abundant capillaries. Mucus secreted by the goblet cells moistens the air and traps dust particles. Drainage from the naso- lacrimal ducts and perhaps secretions from the paranasal sinuses also help moisten the air. The cilia move the mucus and trapped dust particles toward the pharynx, at which point they can be re- moved (i.e., swallowed or spit out) from the respiratory tract.

colon

The open end of the cecum merges with a long tube called the colon ( food passage), which is divided into ascending, trans- verse, descending, and sigmoid portions. Both the ascending and descending colon are retroperitoneal; the transverse and sigmoid colon are not. The ascending colon ascends on the right side of the abdomen, reaches the inferior surface of the liver, and turns abruptly to the left to form the right colic (hepatic) flex- ure. The colon continues across the abdomen to the left side as the transverse colon. It curves beneath the inferior end of the spleen on the left side as the left colic (splenic) flexure and passes inferiorly to the level of the left iliac crest as the descend- ing colon. The sigmoid colon (sigm- S-shaped) begins near the left iliac crest, projects medially to the midline, and termi- nates as the rectum at about the level of the third sacral vertebra.

juxtamedullary nephrons

The other 15-20 percent of the nephrons are juxtamedullary nephrons (juks -ta-MED-u ̄-lar -eˉ; juxta- near to). Their renal corpuscles lie deep in the cortex, close to the medulla, and they have long nephron loops that extend into the deepest region of the medulla (Figure 25.5b).

Several ligaments that are either extensions of the parietal peritoneum or fibromuscular cords main- tain the position of the uterus

The paired broad ligaments are double folds of peritoneum attaching the uterus to either sideˉof the pelvic cavity. The paired uterosacral ligaments (u ̄-ter-oˉ-SA-kral), also peritoneal extensions, lie on either side of the rectum and connect the uterus to the sacrum. The cardinal (lateral cervical) ligaments are located inferior to the bases of the broad ligaments and extend from the pelvic wall to the cervix and vagina. The round ligaments are bands of fibrous connec- tive tissue between the layers of the broad ligament; they extend from a point on the uterus just inferior to the uterine tubes to a portion of the labia majora of the external genitalia. Although the ligaments normally maintain the anteflexed position of the uterus, they also allow the uterine body enough movement that the uterus may become malpositioned.

Histology of the Pancreas

The pancreas is made up of small clusters of glandular epithelial cells, about 99 percent of which are arranged in clusters called acini (AS-i-n ̄ı) and constitute the exocrine portion of the organ (see Figure 22.7b, c). The cells within acini secrete a mixture of fluid and digestive enzymes called pancreatic juice. The remain- ing 1 percent of the cells are organized into clusters called pan- creatic islets (islets of Langerhans) (I ̄-lets), the endocrine por- tion of the pancreas. These cells secrete the hormones glucagon, insulin, somatostatin, and pancreatic polypeptide.

upper esophageal sphincter (UES)

The passage of food from the laryngopharynx into the esophagus is regulated at the entrance to the esophagus by a sphinc- ter (a circular band or ring of muscle that is normally contracted) It con- sists of skeletal muscle (cricopharyngeus muscle) attached to the cricoid cartilage. The elevation of the larynx causes the sphincter to relax, allowing the bolus to enter the esophagus. This sphincter also relaxes during exhalation.

hematocrit

The percentage of total blood volume occupied by RBCs

hemospermia

The presence of blood in semen

chyle

The presence of these lipids causes the lymph draining from the small intestine to appear creamy white; such lymph is referred to as chyle (KI ̄L juice). Elsewhere in the body, lymph is a clear, pale- yellow fluid.

vestibule

The region between the labia minorais

primary spermatocytes

The rest of the cells lose contact with the basement membrane, squeeze through the tight junctions of the blood-testis barrier, undergo developmental changes, and differentiate into primary spermatocytes (SPER-ma-toˉ -s ̄ı tz ). Primary spermatocytes, like spermatogonia, are diploid (2n); that is, they have 46 chromosomes.

fun- dus

The rounded portion superior and to the left of the cardia

gastric juice

The secretions of the mucous, parietal, and chief cells form gastric juice, about 2000-3000 mL (roughly 2-3 qt) per day.

cervical mucus

The secretory cells of the mucosa of the cervix produce a se- cretion called cervical mucus, a mixture of water, glycoproteins, lipids, enzymes, and inorganic salts. During their reproduc- tive years, females secrete 20-60 mL of cervical mucus per day.

peritoneal cavity

The slim space between the parietal and visceral portions of the peritoneum

Anatomy of the Small Intestine

The small intestine is divided into three regions (Figure 24.16). The first part of the small intestine, the duodenum (doo -oˉ - DE ̄ -num), is the shortest region, and is retroperitoneal. Duode- num means "12"; it is so named because it is about as long as the width of 12 fingers. It starts at the pyloric sphincter of the stomach and is in the form of a C-shaped tube that extends about 25 cm (10 in.) until it merges with the next section, called the jejunum. The jejunum (jeˉ-JOO-num), the next portion, is about 1 m (3 ft) long, and extends to the ileum. Jejunum means "empty," which is how it is found at death. The jejunum is mostly in the left upper quadrant (LUQ). The final and longest region of the small intestine, the ileum (IL-eˉ-um twisted), measures about 2 m (6 ft) and joins the large intestine at a smooth muscle sphinc- ter called the ileocecal sphincter (valve) (il -eˉ -oˉ -SE ̄ -kal). The ileum is mostly in the right lower quadrant (RLQ).

corpus spongiosum penis

The smaller midventral mass, the corpus spongiosum penis, contains the spongy urethra and keeps it open during ejaculation. Skin and a subcutaneous layer enclose all three masses, which consist of erectile tissue. Erectile tissue is composed of numerous blood sinuses (vascular spaces) lined by endothelial cells and sur- rounded by smooth muscle and elastic connective tissue.

inguinal canal

The spermatic cord and ilioinguinal nerve pass through the inguinal canal an oblique passageway in the anterior abdom- inal wall just superior and parallel to the medial half of the inguinal ligament. The canal, which is about 4-5 cm (about 2 in.) long, originates at the deep (abdominal) inguinal ring, a slitlike opening in the aponeurosis of the transversus abdominis muscle; the canal ends at the superficial (subcutaneous) in- guinal ring (see Figure 26.2), a somewhat triangular opening in the aponeurosis of the external oblique muscle. In females, the round ligament of the uterus and ilioinguinal nerve pass through the inguinal canal.

metastasis

The spread of cancer from the organ of origin to another part of the body

tunica vaginalis

The testes are partially covered by a serous membrane which is derived from the peritoneum and forms during the descent of the testes. Like other serous membranes, it has a visceral layer and a parietal layer and forms a fist-in-balloon relationship with the testis.

testicles

The testes develop near the kidneys, in the posterior portion of the abdomen, and they usually begin their descent into the scrotum through the inguinal canals (passage- ways in the lower anterior abdominal wall; see Figure 26.2) dur- ing the latter half of the seventh month of fetal development.

secondary spermatocytes

The two cells formed by meiosis I are called secondary spermatocytes. Each secondary spermato- cyte has 23 chromosomes, the haploid number (n). Each chro- mosome within a secondary spermatocyte, however, is made up of two chromatids (two copies of the DNA) still attached by a centromere. No replication of DNA occurs in the secondary spermatocytes.

normal sinus rhythm

The usual rhythm of heartbeats, established by the SA node

nerves of stomach

The vagus (X) nerves convey parasympathetic fibers to the stomach. These fibers form synapses within the submucosal plexus in the submucosa and the myenteric plexus in the muscu- laris. The sympathetic nerves arise from the celiac ganglia, and the nerves reach the stomach along the branches of the celiac artery.

coronary sinus

The vascular sinus in the coronary sulcus on the posterior surface of the heart

Histology of the Small Intestine

The wall of the small intestine is composed of the same four layers that make up most of the GI tract: mucosa, submucosa, muscularis, and serosa (Figure 24.17b). The mucosa is composed of a layer of epithelium, lamina propria, and muscularis mucosae. The epithelial layer of the small intestinal mucosa consists of simple columnar epithelium that contains several types of cells: absorptive, goblet, enteroendocrine, and paneth

oogonia

There, germ cells differentiate within the ovaries Oogonia are diploid (2n) stem cells that divide mitotically to produce millions of germ cells. Even before birth, most of these germ cells degenerate in a process known as atresia (a-TRE ̄ -zeˉ-a). However, a few develop into larger cells called primary oocytes (O ̄ -oˉ -s ̄ı tz) that enter prophase of meiosis I during fetal development but do not complete that phase until after puberty

Hepatic sinusoids

These highly permeable blood capil- laries between hepatic laminae receive oxygenated blood from branches of the hepatic artery and nutrient-rich deoxygenated blood from branches of the hepatic portal vein. Recall that the hepatic portal vein brings venous blood from the gastrointes- tinal organs and spleen into the liver. Hepatic sinusoids con- verge and deliver blood into a central vein. From central veins the blood flows into the hepatic veins, which drain into the inferior vena cava (see Figure 14.5). Whereas blood flows

Lymph Nodes

They are scattered throughout the body, both superficially and deep, and usually occur in groups .Large groups of lymph nodes are present near the mammary glands and in the axillae and groin. Later in the chapter, the principal groups of lymph nodes in various regions of the body will be presented in a series of exhibits. like the thymus, are covered by a capsule of dense connective tissue that extends into the node). The capsular extensions, called trabeculae, divide the node into compartments, give sup- port, and provide a route for blood vessels into the interior of a node. Internal to the capsule is a supporting network of reticu- lar fibers and fibroblasts. The capsule, trabeculae, reticular fib- ers, and fibroblasts constitute the stroma (framework tissue) of a lymph node.

erythropoietin (EPO)

This in turn stimulates the synthesis of a hormone

Portal lobule

This model emphasizes the exocrine function of the liver, that is, bile secretion. Accordingly, the bile duct of a portal triad is taken as the center of the portal lobule. The triangular shape of the portal lobule is defined by three imagi- nary straight lines that connect three central veins closest to the portal triad (Figure 24.14d, center). This model has not gained widespread acceptance.

endoderm

This new layer of cells forming the roof of the yolk sac Epithelial lining of gastrointestinal tract (except the oral cavity and anal canal) and the epithelium of its glands Epithelial lining of urinary bladder, gallbladder, and liver Epithelial lining of pharynx, auditory (eustachian) tubes, tonsils, tympanic (middle ear) cavity, larynx, trachea, bronchi, and lungs Epithelium of thyroid gland, parathyroid glands, pancreas, and thymus Epithelial lining of prostate and bulbourethral (Cowper's) glands, vagina, vestibule, urethra, and associated glands such as the greater vestibular (Bartholin's) and lesser vestibular glands Gametes (sperm and oocytes)

Serosa

Those portions of the GI tract that are suspended in the abdomi- nal cavity have a superficial layer called the serosa. As its name implies, the serosa is a serous membrane composed of areolar connective tissue and simple squamous epithelium (mesothe- lium). The epithelial portion of the serosa is also called the vis- ceral peritoneum because it forms the portion of the peritoneum that surrounds the organs suspended in the peritoneal cavity, which we will examine in detail shortly. The name serous mem- brane arises from the fact that the epithelium has a lubricating coat of serous fluid, a watery solution of electrolytes and other sol- utes derived from interstitial fluid of the adjacent tissues, along with blood plasma from local capillaries. The serous fluid also contains various white blood cells. When the highly coiled diges- tive tube rubs against neighboring areas of the tube or against the inside of the body wall, the serous membrane protects the outer wall of the gut from abrasion. The esophagus and lower aspect of the rectum are the only organs of the GI tract that completely lack a serosa; instead, only a single layer of areolar connective tissue called the adventitia surrounds them.

conchae

Three shelves called conchae, formed by projections of the superior, middle, and inferior nasal conchae, extend out of each lateral wall of the nasal cavity. The conchae, almost reach- ing the bony nasal septum, subdivide each side of the nasal cavity into a series of groove-like passageways—the superior, middle, and inferior nasal meatuses (meˉ-Aˉ-tus-eˉz openings or pas- sages). A mucous membrane lines the nasal cavity and its shelves. The arrangement of conchae and meatuses increases surface area in the nasal cavity and prevents dehydration by acting as a baffle that traps water droplets during exhalation.

Each lobe receives its own lobar bronchus

Thus, the right main bronchus gives rise to three lobar bronchi called the superior, middle, and inferior lobar bronchi, and the left main bronchus gives rise to superior and inferior lobar bronchi. Within the lung, the lobar bronchi give rise to the segmental bronchi; there are 10 segmental bronchi in each lung. The segment of lung tissue that each segmental bronchus supplies is called a broncho- pulmonary segment (brong -koˉ-PUL-moˉ-nar -eˉ) (Figure 23.9). Bronchial and pulmonary disorders (such as tumors or abscesses) that are localized in a particular bronchopulmonary segment may be surgically removed without seriously disrupting the surrounding lung tissue.

filtration membrane or endothelial-capsular mem- brane.

Together, glomerular capillaries and podocytes, which com- pletely encircle the glomerulus, form a leaky barrier referred to

haustra

Tonic contractions of the bands gather the colon into a series of pouches

Events in the Ovaries

Under the influence of FSH, several primordial follicles develop into primary follicles and then into secondary follicles. Follicular fluid, secreted by the granulosa cells and filtered from blood in the capillaries of the theca folliculi, accumulates in the enlarging antrum (space that forms within the follicle) while the oocyte re- mains near the edge of the follicle

tonsils

Usually there are five tonsils, which form a tonsillar (Waldeyer's) ring at the junction of the oral cavity and oropharynx and at the junction of the nasal cavity and nasopharynx (see Figure 23.2b). The single pharyngeal tonsil (fa-RIN-jeˉ-al) or adenoid is embedded in the posterior wall of the nasopharynx. This pyramid-shaped mass of lymphoid tissue is covered with a mucous membrane. The two palatinetonsils(PAL-a-t ̄ın)lieinthelateralwalloftheorophar- ynx in the tonsilar fossa just inferior to the soft palate; these are the tonsils commonly removed in a tonsillectomy. The almond- shaped palatine tonsils have numerous branched crypts that form a surface area of approximately 300 cm2 (118 in.2). The paired lin- gual tonsils (LIN-gwal), located at the base of the tongue, may also require removal during a tonsillectomy. The tonsils are strategically positioned to participate in immune responses against inhaled or ingested foreign substances. Tonsils are masses of lymphoid tissue covered with mucosal epithelium. The epithelium forms narrow invaginations, called crypts, into the lymphoid tissue below. The crypts greatly increase the mucosal surface associated with the lym- phoid tissue. In the crypts the mucosa becomes very thin, forming patches of reticulated epithelium. This specialized epithelium is well-designed for the transfer of antigen from the environment of the oral cavity and pharynx to the lymphoid cells of the tonsils.

Defecation

Wastes, indigestible substances, bacteria, cells sloughed from the lining of the GI tract, and digested materi- als that were not absorbed leave the body through the anus as feces

allantois

When the cloacal membrane appears, the wall of the yolk sac forms a small vascularized outpouching

blood supply to kidneys

Within the kidney, the renal artery divides into several seg- mental arteries (seg-MENT-al), which supply different seg- ments (areas) of the kidney. Each segmental artery gives off several branches that enter the parenchyma and pass through the renal columns between the renal lobes of the kidneys as the interlobar arteries (in -ter-LO ̄ -bar). A renal lobe consists of single renal vein that exits at the renal hilum and carries venous blood to the inferior vena cava.

nephron

Within the parenchyma are the functional units of the kidney—about 1 million microscopic structures

lingual frenulum

a fold of mucous membrane in the midline of the undersurface of the tongue, is attached to the floor of the mouth and aids in limiting the movement of the tongue posteri- orly

greater omentum

a large peri- toneal fold, drapes over the transverse colon and coils of the small intestine like a "fatty apron" (Figure 24.3). The greater omentum is a double sheet that folds back upon itself, giving it a total of four layers. From attachments along the greater curvature of the stomach and initial part of the duodenum, the greater omentum extends downward anterior to the small intestine, then turns and extends upward and attaches to the transverse colon. The greater omentum normally contains a considerable amount of adipose tis- sue. Its adipose tissue content can greatly expand with weight gain, contributing to the characteristic "beer belly" seen in some over- weight individuals. The many lymph nodes of the greater omen- tum contribute macrophages and antibody-producing plasma cells that help combat and contain infections of the GI tract.

The liver is divided into two principal lobes

a large right lobe and a smaller left lobe—by the falciform ligament, a mesenteric fold from the parietal peritoneum of the diaphragm and anterior abdom- inal wall to the visceral peritoneum of the liver (Figures 24.12 and 24.13). The right lobe is considered by many anatomists to include an inferior quadrate lobe (KWA-dra ̄t) and a poste- rior caudate lobe (KAW-da ̄t). However, on the basis of inter- nal morphology (primarily the distribution of blood vessels), the quadrate and caudate lobes more appropriately belong to the left lobe. The falciform ligament extends from the undersurface of the diaphragm between the two principal lobes of the liver to the superior surface of the liver, helping to suspend the liver in the abdominal cavity. The free border of the falciform ligament is the ligamentum teres (round ligament), a fibrous cord that is a remnant of the umbilical vein of the fetus; it extends from the liver to the umbilicus. The right and left coronary ligaments are narrow extensions of the parietal peritoneum that suspend the liver from the diaphragm

basal lamina

a layer of material between the endothe- lium of the glomerulus and the podocytes, consists of minute fibers in a glycoprotein matrix; negative charges within this matrix prevent filtration of larger negatively charged plasma proteins.

mammary gland

a modified sudorifer- ous (sweat) gland that produces milk (Figure 26.23). A mammary gland consists of 15 to 20 lobes, or compartments, separated by a variable amount of adipose tissue. In each lobe are several smaller compartments called lobules, composed of grapelike clusters of milk-secreting glands termed alveoli (al-VE ̄ -oˉ-lı ̄ small cavities) embedded in connective tissue (Figure 26.24). Contraction of myoepithelial cells (mı ̄ -oˉ-ep -i-THE ̄ -leˉ-al) surrounding the alveoli helps propel milk toward the nipples. When milk is being produced, it passes from the alveoli into a series of secondary tubules and then into the mammary ducts. Near the nipple, the mammary ducts expand slightly to form sinuses called lactifer- ous sinuses (lact- milk), where some milk may be stored before draining into a lactiferous duct. Each lactiferous duct typically carries milk from one of the lobes to the exterior.

Each somite differentiates into three regions

a myotome (MI ̄ -o-to ̄ m), a dermatome (DERM-a-to ̄ m), and a sclerotome (SKLE-ro-to ̄m) (see Figure 10.11b, c). The myotomes develop into the skeletal muscles of the neck, trunk, and limbs; the der- matomes form connective tissue, including the dermis of the skin; and the sclerotomes give rise to the vertebrae and ribs.

induction

a process in which one tissue (inducing tissue) stimulates the specialization of an adjacent tissue (responding tissue).

Food is pushed through the esophagus by

a progression of involuntary coordinated contractions and relaxations of the cir- cular and longitudinal layers of the muscularis called peristalsis (per -i-STAL-sis; stalsis constriction). Peristalsis occurs in other tubular structures, including other portions of the GI tract, the ureters, bile ducts, and uterine tubes; in the esophagus it is con- trolled by the medulla oblongata. The steps of peristalsis are as follows (Figure 24.9): 1. The circular muscle fibers in the section of the esophagus above the bolus contract, constricting the wall of the es- ophagus and squeezing the bolus downward. 2. Longitudinal muscle fibers around the bottom of the bolus contract, shortening the section below the bolus and pushing its walls outward. 3. After the bolus moves into the new section of the esophagus, the circular muscles above it contract, and the cycle repeats. The contractions move the bolus down the esophagus toward the stomach. As the bolus approaches the end of the esopha- gus, the lower esophageal sphincter relaxes and the bolus moves into the stomach.

Each nephron consists of two parts:

a renal corpuscle ,where blood plasma is filtered, and a renal tubule into which the filtered fluid (glomerular filtrate) passes.

pancreas

a retroperitoneal gland that is about 12-15 cm (5-6 in.) long and 2.5 cm (1 in.) thick, lies posterior to the greater curvature of the stomach (see Figure 24.1). Along with the liver and gallbladder, it develops as an embryonic epithelial outgrowth of the duodenum. The pancreas consists of a head, a body, and a tail and is usually connected to the duode- num by two ducts (Figure 24.12a, c, d). The head is the expanded portion of the organ near the curve of the duodenum. Projecting from the lower portion of the head is the hooklike uncinate proc- ess that arches behind the superior mesenteric artery and vein, encircling them with pancreatic tissue. Superior to and to the left of the head are the central body and the tapering tail.

sinuses

a series of irregular channels that contain branching reticular fibers, lymphocytes, and macrophages. From the afferent lymphatic vessels, lymph flows into the subcapsular sinus (sub-KAP-soo-lar) immedi- ately beneath the capsule. From there the lymph flows through trabecular sinuses (tra-BEK-u ̄-lar), which extend through the cortex parallel to the trabeculae, and into medullary sinuses, which extend through the medulla. The medullary sinuses drain into one or two efferent lymphatic vessels (EF-er-ent to carry away), which are wider than afferent vessels and fewer in number. They contain valves that open away from the center of the lymph node to convey lymph, antibodies secreted by plasma cells, and activated T cells out of the lymph node. Efferent lym- phatic vessels emerge from one side of the lymph node at a slight depression called a hilum (HI ̄-lum). Blood vessels also enter and leave the node at the hilum.

The mucous membrane of the larynx forms two pairs of folds

a superior pair called the vestibular folds (false vocal cords) and an inferior pair called simply the vocal folds (true vocal cords). The space between the vestibular folds is known as the rima vestibuli. The laryngeal ventricle (sinus) is a lateral expansion of the middle portion of the laryngeal cav- ity; it is bordered superiorly by the vestibular folds and inferiorly by the vocal folds. While the vestibular folds do not function in voice production, they do have other important functional roles. When the vestibular folds are brought together, they function in holding the breath against pressure in the thoracic cavity, such as might occur when a person strains to lift a heavy object.

calcitonin

acts to reduce blood calcium (Ca2+), opposing the effects of parathyroid hormone (PTH)

uterine tubes

also called fallopian tubes or oviducts, that extend laterally from the uterus (Figure 26.16). The tubes, which measure about 10 cm (4 in.) long and lie within the folds of the broad ligaments of the uterus, trans- port secondary oocytes and fertilized ova from the ovaries to the uterus.

menstrual phase

also called menstrua- tion (men -stroo-Aˉ -shun) or menses ( month), lasts for roughly the first 5 days of the cycle. (By convention, the first day of men- struation is day one of a new cycle.)

Type II alveolar cells

also called septal cells, are fewer in number and are found between type I alveolar cells. The thin type I alveolar cells are the main sites of gas exchange. Type II alveolar cells, which are rounded or cuboidal epithelial cells with free surfaces contain- ing microvilli, secrete alveolar fluid. This fluid keeps the surface between the cells and the air moist. Included in the alveolar fluid is surfactant (sur-FAK-tant), a complex mixture of phospholipids and lipoproteins. Surfactant lowers the surface tension of alveolar fluid, which reduces the tendency of alveoli to collapse and thus maintains their patency (described later).

inner cortex

also called the paracortex, does not contain lymphatic nodules. It consists mainly of T cells and dendritic cells that enter a lymph node from other tissues. The dendritic cells present antigens to T cells, causing the T cells to proliferate. The newly formed T cells then migrate from the lymph node to areas of the body where there is antigenic activity.

prolactin

also known as luteotropic hormone or luteotropin, is a protein that is best known for its role in enabling mammals, usually females, to produce milk. It is influential in over 300 separate processes in various vertebrates, including humans.

lesser vestibular glands

also open into the vestibule

four different kinds of extraembryonic membranes to protect the embryo:

amnion, yolk sac, allantois, and chorion.

where does fertilization occur

ampulla

The primitive gut elongates and differentiates into

an anterior foregut, an intermediate midgut, and a posterior hindgut (see Figure 4.12c). Until the fifth week of development, the midgut opens into the yolk sac; after that time, the yolk sac constricts and detaches from the midgut, and the midgut seals. the foregut, a depression consisting of ectoderm, the stomodeum (stoˉ -moˉ -DE ̄ -um), appears (see Figure 4.12d). This develops into the oral cavity.

The wall of a blood vessel consists of three layers, or tunics, of different tissues:

an endothelial inner lining, a middle layer con- sisting of smooth muscle and elastic connective tissue, and a con- nective tissue outer covering. (Recall that the term endothelium refers to simple squamous epithelium that lines the cardiovascu- lar and lymphatic systems.) From innermost to outermost, the three structural layers of a generalized blood vessel are the tunica interna (intima), tunica media, and tunica externa (adventitia)

pancreatic lipase

an enzyme secreted by the pancreas into the small intestine

The muscularis is composed of

an outer longitudinal layer and an inner circular layer of smooth muscle (Figure 26.20a) that can stretch considerably to accommodate the penis during sexual in- tercourse and an infant during birth.

These chemoreceptors are part of the peripheral nervous system

and are sensitive to changes in O2, H , and CO2 in the blood. Axons of sensory neurons from the aortic bodies are part of the vagus (X) nerves, and those from the carotid bodies are part of the right and left glossopharyngeal (IX) nerves and vagus (X) nerves

Lingual lipase

and mucus are secreted by lingual glands on the dorsum (upper surface) of the tongue. This enzyme, which is active in the stomach, can digest as much as 30 percent of dietary triglyc- erides (fats and oils) into simpler fatty acids and diglycerides

The location of the scrotum

and the contraction of its mus- cle fibers regulate the temperature of the testes. Normal sperm production requires a temperature about 2-3 C below core body temperature. This lowered temperature is maintained within the scrotum because it is outside the pelvic cavity. In response to cold temperatures, the cremaster and dartos muscles contract. Con- traction of the cremaster muscles moves the testes closer to the body, where they can absorb body heat. Contraction of the dar- tos muscle causes the scrotum to become tight (wrinkled in ap- pearance), which reduces heat loss. Exposure to warmth reverses these actions.

secondary lymphatic organs

and tissues are the sites where most immune responses occur. They include lymph nodes, the spleen, and lymphatic nodules (follicles)

teeth

are accessory digestive or- gans located in sockets of the alveolar processes of the mandible and maxillae. The alveolar processes are covered by the gingi- vae (jin-JI-veˉ), or gums, which extend slightly into each socket to form the gingival sulcus. The sockets are lined by the periodon- tal ligament or membrane (per -eˉ -oˉ -DON-tal; odont- tooth), which consists of dense fibrous connective tissue and is attached to the socket walls and outer covering (cementum) of the roots of the teeth. The periodontal ligament anchors the teeth in position and acts as a shock absorber during chewing.

lips or labia

are fleshy folds surround- ing the opening of the mouth. They contain the orbicularis oris muscle and are covered externally by skin and internally by a mu- cous membrane.

Three types of enteroendocrine cells

are found in the intestinal glands of the small intestine: S cells, CCK cells, and K cells, which secrete the hormones secretin (se-KRE ̄ -tin), cholecystokinin (CCK) (koˉ- le-sis -toˉ-KI ̄ N-in), and glucose-dependent insulinotropic peptide (GIP) (in-soo-lin-oˉ -TRO ̄ -pik), respectively.

Segmentations

are localized, mixing contractions that occur in portions of the intestine distended by a large volume of chyme. Segmentations mix chyme with the di- gestive juices and bring the particles of food into contact with the mucosa for absorption; they do not push the intestinal contents

Peripheral chemoreceptors

are located in the aortic bodies, clusters of chemoreceptors located in the wall of the arch of the aorta, and in the carotid bodies, which are oval nodules in the wall of the left and right common carotid arter- ies where they divide into the internal and external carotid arteries.

Central chemore- ceptors

are located in the medulla oblongata in the central nerv- ous system. They respond to changes in H or CO2 concentration, or both, in cerebrospinal fluid.

Ovarian follicles

are located in the ovar- ian cortex and consist of oocytes (O ̄ -oˉ-s ̄ıts) in various stages of development, plus the cells surrounding them. When the sur- rounding cells form a single layer, they are called follicular cells (foˉ-LIK-u ̄-lar); later in development, when they form several layers, they are referred to as granulosa cells (gran-u ̄- LO ̄ -sa). The surrounding cells nourish the developing oocyte and begin to secrete estrogens as the follicle grows larger.

lungs

are paired cone-shaped organs in the thoracic cavity. The lungs are separated from each other by the heart and other structures of the mediastinum, which separates the thoracic cavity into two ana- tomically distinct chambers. Because of this separation, if trauma causes one lung to collapse, the other may remain expanded.

kidneys

are reddish, kidney-bean-shaped organs located just above the waist between the peritoneum and the posterior wall of the abdomen. Because their position is poste- rior to the peritoneum of the abdominal cavity, they are said to be retroperitoneal organs. The kidneys are located between the lev- els of the last thoracic and third lumbar vertebrae, a position where they are partially protected by ribs 11 and 12. This is a double-edged sword, however, because if these lower ribs are fractured they can slice into the kidneys and create significant, even life-threatening, damage. The right kidney is slightly lower than the left (see Figure 25.1) because the liver occupies considerable space on the right side superior to the kidney.

Elastic arteries

are the largest arteries in the body, ranging from the garden hose-sized aorta and pulmonary trunk to the finger- sized branches of the aorta. They have the largest diameter among arteries, but their vessel walls (approximately one-tenth of the vessel's total diameter) are relatively thin compared to the overall size of the vessel. These vessels are characterized by well-defined internal and external elastic laminae, along with a thick tunica media that is dominated by elastic fibers, the elastic lamellae

primary germ layers

are the major embryonic tissues from which the various tissues and organs of the body develop.

Type I (anaphylactic) reactions

are the most common type of allergic reaction and occur within a few minutes after a person previously exposed to an allergen is reexposed to it. In response to the first exposure to certain allergens, some people produce antibod- ies that bind to the surface of mast cells and basophils. The next time the same allergen enters the body, it attaches to the antibodies already present. In response, the mast cells and basophils release chemicals such as histamine. These mediators cause vasodilation, increased blood capil- lary permeability, increased smooth muscle contraction in the airways of the lungs, and increased mucus secretion. As a result, a person may experience inflammatory responses, difficulty in breathing through the constricted airways, and a runny nose from excess mucus secretion. In anaphylactic shock, which may occur in a susceptible individual who has just received a triggering drug or been stung by a wasp, wheezing and shortness of breath as airways constrict are usually accompanied by shock due to vasodilation and fluid loss from blood. This life-threaten- ing emergency is usually treated by injecting epinephrine to dilate the airways and strengthen the heartbeat.

Primary lymphatic organs

are the sites where stem cells divide and become immunocompetent , that is, ca- pable of mounting an immune response. The primary lymphatic organs are the red bone marrow (in flat bones and the epiphyses of some long bones of adults) and the thymus

The functions of the mammary glands

are the synthesis, secre- tion, and ejection of milk; these functions, called lactation (lak- TAˉ-shun), are associated with pregnancy and childbirth. Milk production is stimulated largely by the hormone prolactin from the anterior pituitary, with contributions from progesterone and estrogens. The ejection of milk is stimulated by oxytocin, which is released from the posterior pituitary in response to the sucking of an infant on the mother's nipple (suckling).

arytenoid cartilages

are triangular pieces of mostly hyaline cartilage located at the posterior, superior border of the cricoid cartilage. They form synovial joints with the cricoid cartilage and have a wide range of mobility.

Sinusoids

are wider and more wind- ing than other capillaries.

lesser omentum

arises as an anterior fold of the serosa of the stomach and duodenum. It connects the stomach and duo- denum to the liver (Figure 24.3a, c). It is the pathway of blood vessels entering the liver and contains the hepatic portal vein, the common hepatic artery, and the common bile duct, along with some lymph nodes.

falciform ligament

attaches the liver to the anterior abdominal wall and diaphragm (Figure 24.3b, e). This remnant of the ventral mesentery of the embryo was the path of the umbilical vein from the umbilical cord to the inferior vena cava in the fetus. The liver is the only digestive organ that is attached to the anterior abdominal wall.

The nerves to the pancreas are

autonomic nerves that branch from the celiac and superior mesenteric plexuses. Included are preganglionic vagal, postganglionic sympathetic, and sensory fib- ers. Parasympathetic vagal fibers are said to terminate at both acinar (exocrine) and islet (endocrine) cells. Although the in- nervation is presumed to influence enzyme formation, pancre- atic secretion is controlled largely by the hormones secretin and cholecystokinin (CCK) released by the small intestine. The sym- pathetic fibers enter the islets and also end on blood vessels; these fibers are vasomotor and accompanied by sensory fibers, espe- cially for pain.

blood-testis barrier

because substances must pass through the sustentacular cells before they can reach the developing sperm. By isolating the developing gametes from the blood, the blood- testis barrier prevents an immune response against the sperma- togenic cell's surface antigens, which are recognized as "foreign" by the immune system. The blood-testis barrier does not include spermatogonia.

nephron loop

begins at the point where the proximal convoluted tubule takes its final turn downward.

mesocolon

bind the transverse colon (transverse mesocolon) and sigmoid colon (sigmoid mesocolon) of the large intestine to the posterior abdominal wall (Figure 24.3a); these folds carry blood vessels (superior and inferior mesenteric vessels) and lym- phatic vessels to the intestines. The mesentery and mesocolon hold the intestines loosely in place, allowing for a great amount of movement as muscular contractions mix and move the intestinal contents along the GI tract.

portal system

blood passes from one capillary network into another through a vessel called a portal vessel.

• Secondary sexual characteristics

body fat distribution, voice pitch, facial hair, breast development

The nerves of the larynx are

both branches of the vagus (X) nerve. The superior laryngeal nerve enters the larynx from above, and the recurrent laryngeal nerve ascends through the base of the neck to enter the larynx from below.

The sensory nerves to the penis are

branches from the puden- dal and ilioinguinal nerves. The corpora have a parasympathetic and a sympathetic supply. As noted previously, parasympathetic stimulation causes the blood vessels to dilate, increasing the flow of blood into the erectile tissue and trapping blood within the penis to maintain the erection. At ejaculation, sympathetic stimu- lation causes the smooth muscle located in the walls of the ducts and accessory sex glands of the reproductive tract to contract and propel the semen along its course.

The parotid gland receives its blood supply from

branches of the external carotid artery and is drained by tributaries of the exter- nal jugular vein. The submandibular gland is supplied by branches of the facial artery and drained by tributaries of the facial vein. The sublingual gland is supplied by the sublingual branch of the lingual artery and the submental branch of the facial artery and is drained by tributaries of the sublingual and submental veins.

The arteries of the trachea are

branches of the inferior thy- roid, internal thoracic, and bronchial arteries. The veins of the trachea terminate in the inferior thyroid veins.

The teeth receive sensory fibers from

branches of the maxillary and mandibular divisions of the trigeminal (V) nerve. The maxil- lary teeth receive sensory fibers from branches of the maxillary division, and the mandibular teeth receive theirs from branches of the mandibular division.

The parts of the gallbladder are the

broad fundus, which projects downward beyond the inferior border of the liver; the central portion, called the body; and a tapered portion called the neck. The body and neck project superiorly

The gallbladder is supplied by

by the cystic artery, which usually arises from the right hepatic artery. The cystic veins drain the gallbladder. The nerves to the gallbladder include branches from the celiac plexus and the vagus (X) nerve.

chief (zymogenic) cells

cells secrete pep- sinogen and gastric lipase.

All the chemical and mechanical phases of digestion from the mouth through the small intestine are directed toward

chang- ing food into forms that can pass through the epithelial cells lin- ing the mucosa into the underlying blood and lymphatic vessels. These forms are monosaccharides (glucose, fructose, and galac- tose) from carbohydrates; single amino acids, dipeptides, and tripeptides from proteins; fatty acids, glycerol, and monoglycer- ides from lipids; and pentoses and nitrogenous bases from nucleic acids. Passage of these digested nutrients from the gastrointesti- nal tract into the blood or lymph is called absorption. Absorp- tion occurs by diffusion, facilitated diffusion, osmosis, and active transport.

The final stage of digestion occurs in the

colon through the ac- tivity of bacteria that inhabit the lumen. Mucus is secreted by the glands of the large intestine, but no enzymes are secreted. Chyme is prepared for elimination by the action of bacteria, which fer- ment any remaining carbohydrates and release hydrogen, carbon dioxide, and methane gases. These gases contribute to flatus (gas) in the colon, termed flatulence when it is excessive. Bacteria also convert any remaining proteins to amino acids and break down the amino acids into simpler substances: indole, skatole, hydro- gen sulfide, and fatty acids. Some of the indole and skatole is eliminated in the feces and contributes to their odor; the rest is absorbed and transported to the liver, where these compounds are converted to less toxic compounds and excreted in the urine. Bacteria also decompose bilirubin to simpler pigments, including stercobilin, which gives feces their brown color. Several vitamins needed for normal metabolism, including some B vitamins and vitamin K, are bacterial products that are absorbed in the colon. By the time chyme has remained in the large intestine 3-10 hours, it has become solid or semisolid as a result of water absorp- tion and is now called feces. Chemically, feces consist of water, inorganic salts, sloughed-off epithelial cells from the mucosa of the gastrointestinal tract, bacteria, products of bacterial decomposi- tion, unabsorbed digested materials, and indigestible parts of food.

renal lobe

consists of a renal pyramid, its overlying area of renal cortex, and one-half of each adjacent renal column.

cremaster muscle

consists of a series of small bands of skeletal muscle that descend, as an extension of the internal oblique muscle, through the spermatic cord to sur- round the testis.

urinary system

consists of two kidneys, two ureters, one urinary bladder, and one urethra After the kidneys filter blood plasma, they return most of the water and solutes to the bloodstream. The remaining water and solutes constitute urine, which passes through the ureters and is stored in the urinary bladder until it is removed from the body through the urethra. The kidneys do the major work of the urinary system. The other parts of the system are mainly passageways and storage areas.

The medulla

consists of widely scattered, more mature T cells, epithelial cells, dendritic cells, and macrophages Some of the epithelial cells become arranged into con- centric layers of flat cells that degenerate and become filled with keratohyalin granules and keratin. These clusters are called thymic corpuscles or Hassall's corpuscles.

Once sexual stimulation of the penis has ended, the arterioles supplying the erectile tissue of the penis

constrict and the smooth muscle within erectile tissue contracts, making the blood sinuses smaller. This relieves pressure on the veins draining the penis and allows the blood to drain through them. Consequently, the penis returns to its flaccid (relaxed) state.

The medulla of a lymph node

contains B cells, antibody- producing plasma cells that have migrated out of the cortex into the medulla, and macrophages. The various cells are embed- ded in a network of reticular fibers and reticular cells.

corpus luteum

contains the remnants of a mature follicle after ovulation. The corpus luteum produces progesterone, estrogens, relaxin, and inhibin until it degener- ates into fibrous scar tissue called the corpus albicans

). Functionally, the ductus deferens

conveys sperm during sexual arousal from the epididymis toward the urethra by peristaltic contractions of its muscular coat. Like the epididymis, the ductus deferens also can store sperm for several months. Any stored sperm that are not ejaculated by that time are eventually reabsorbed.

The body of the clitoris has two bodies of erectile tissue

corpora cavernosa

During their reproductive years, nonpregnant females normally exhibit

cyclical changes in the ovaries and uterus. Each cycle takes about a month and involves both oogenesis and preparation of the uterus to receive a fertilized ovum. Hormones secreted by the hypothalamus, anterior pituitary, and ovaries control the main events. The ovarian cycle is a series of events in the ovaries that occur during and after the maturation of an oocyte. Ster- oid hormones released by the ovaries control the uterine (men- strual) cycle, a concurrent series of changes in the endometrium of the uterus to prepare it for the arrival and development of a fertilized ovum. If fertilization does not occur, levels of ovarian hormones decrease, which causes the stratum functionalis of the endometrium to slough off. The general term female repro- ductive cycle encompasses the ovarian and uterine cycles, the hormonal changes that regulate them, and the related cyclical changes in the breasts and cervix.

vasoconstriction

de- crease in the diameter of the lumen of a blood vessel increase in sympathetic stimulation typically stimulates the smooth muscle to contract, squeezing the vessel wall and narrowing the lumen.

The arterial supply of the cecum and colon is

derived from branches of the superior mesenteric and inferior mesenteric arter- ies. The distal end of the transverse colon, near the left colic flex- ure, is the transition zone between superior and inferior mesenteric blood supply and drainage. Within this zone the two vessels form numerous collateral circuits. The venous return is by way of the superior and inferior mesenteric veins ultimately to the hepatic portal vein and into the liver. The arterial supply of the rectum and anal canal branches from the superior, middle, and inferior rectal arteries. The rectal veins correspond to the rectal arteries.

The nerve supply of the lungs is

derived from the pulmonary plexus, located anterior and posterior to the roots of the lungs. The pulmonary plexus is formed by branches of the vagus (X) nerves and sympathetic trunks. Motor parasympathetic fibers arise from the dorsal nucleus of the vagus (X) nerve, and motor sympathetic fibers are postganglionic fibers of the second to fifth thoracic paravertebral ganglia of the sympathetic trunk.

Müllerian-inhibiting substance (MIS),

developing sustentacular cells secrete a hormone which causes apoptosis of cells within the paramesone- phric (Müllerian) ducts

The arteries that supply blood to the teeth are

distributed to the pulp cavity and surrounding periodontal ligament. These in- clude the superior alveolar branches of the maxillary artery (an- terior and posterior) and the incisive and dental branches of the inferior alveolar artery.

scrotal septum

divides the scrotum into two sacs, each containing a single testis. The septum is made up of a subcutaneous layer and mus- cle tissue called the dartos muscle which is composed of bundles of smooth muscle fibers. The dartos muscle is also found in the subcutaneous layer of the scrotum.

five pairs of pharyngeal arches (fa-RIN-je ̄-al) or branchial arches (BRAN-ke ̄-al; branch gill) begin to develop on

each side of the future head and neck regions during the fourth week

The arterial supply of the stomach arises

from the celiac trunk. The right and left gastric arteries form an anastomosing arch along the lesser curvature, and the right and left gastro-omental arteries form a similar arch on the greater curvature. Short gastric arteries supply the fundus. The veins of the same name accom- pany the arteries and drain, directly or indirectly, into the hepatic portal vein.

The male and female gonads develop from

gonadal ridges that arise from growth of the intermediate mesoderm. During the fifth week of development, the gonadal ridges appear as bulges just medial to the mesonephros (intermediate kidney) (Fig- ure 26.26). Adjacent to the gonads are the mesonephric ducts (mez -oˉ -NEF-rik) or Wolffian ducts (WULF-eˉ -an), which even- tually develop into structures of the reproductive system in males. A second pair of ducts, the paramesonephric ducts (par -a- mes -oˉ -NEF-rik) or Müllerian ducts (mil-E-reˉ -an), develop lat- eral to the mesonephric ducts and eventually form structures of the reproductive system in females. Both sets of ducts empty into the urogenital sinus. An early embryo has the potential to follow either the male or the female pattern of development because it contains both sets of ducts and genital ridges that can differenti- ate into either testes or ovaries.

laryngopharynx

hypopharynx, begins at the level of the hyoid bone. At its inferior end, it opens into the esopha- gus (food tube) posteriorly and the larynx (voice box) anteriorly. Like the oropharynx, the laryngopharynx is both a respiratory and a digestive pathway and is lined by nonkeratinized stratified squamous epithelium.

seminal vesicles

in length, lying posterior to and at the base of the urinary bladder anterior to the rectum (Figure 26.9). Through the seminal vesicle ducts they secrete an alkaline, viscous fluid that contains fructose (a mono- saccharide sugar), prostaglandins, and clotting proteins (discussed shortly) unlike those found in blood. The alkaline nature of the fluid helps to neutralize the acidic environment of the male ure- thra and female reproductive tract that otherwise would inacti- vate and kill sperm. The fructose is used for the production of ATP by sperm. Prostaglandins contribute to sperm motility and viability and may also stimulate muscular contractions within the female reproductive tract. The clotting proteins help semen coagulate after ejaculation. Fluid secreted by the seminal vesicles normally constitutes about 60 percent of the volume of semen.

vasectomy

in which a portion of each ductus deferens is removed. An incision is made on either side of the scrotum, the ducts are located and cut, each is tied (ligated) in two places with stitches, and the portion between the ties is removed. Although sperm production continues in the testes, sperm can no longer reach the exterior. The sperm degenerate and are destroyed by phagocytosis. Because the blood vessels are not cut, testosterone levels in the blood remain normal, so vasectomy has no effect on sex- ual desire, performance, and ejaculation. If done correctly, vasectomy is close to 100 percent effective. The procedure can be reversed, but the chance of regaining fertility is only 30-40 percent.

tubal ligation

in which both uterine tubes are tied closed and then cut. This can be achieved in a few different ways. "Clips" or "clamps" can be placed on the uterine tubes, the tubes can be tied and/or cut, and sometimes the tubes are cauterized. In any case, the result is that the secondary oocyte cannot pass through the uterine tubes, and sperm cannot reach the oocyte.

male reproductive system

include the testes (male gonads), a system of ducts (including the epididymis, duc- tus deferens, ejaculatory ducts, and urethra), accessory sex glands (seminal vesicles, prostate, and bulbourethral glands), and sev- eral supporting structures, including the scrotum and the penis

vasodilation

increase in lumen diameter when sympathetic stimulation decreases

Overall, the digestive system performs six basic functions:

ingestion secretion mixing and propulsion digestion absorption defecation

From scrotum >

inguinal canal > arches over ureter > descends behind bladder > joins seminal vescicle > ejaculatory duct > through prostrate gland > merges with urethra

The smooth muscle and glands of the trachea are

innervated parasympathetically by branches of the vagus (X) nerves. Sym- pathetic innervation is through branches from the sympathetic trunk and its ganglia.

prostatic urethra

is 2-3 cm (1 in.) long and passes through the prostate. As this duct continues inferiorly, it passes through the deep muscles of the perineum (see Figure 11.15), where it is known as the intermediate (mem- branous) urethra

thymus

is a bilobed organ located in the mediastinum be- tween the sternum and the aorta. It extends from the top of the sternum or the inferior cervical region to the level of the fourth costal cartilages, anterior to the top of the heart and its great ves- sels Extensions of the capsule, called trabeculae, penetrate inward and divide each lobe into lobules

epididymis

is a comma- shaped organ about 4 cm (1.5 in.) long that lies along the posterior border of each testis (see Figure 26.3b). Each epididymis consists mostly of the tightly coiled ductus epididymis. The efferent ducts from the testis join the ductus epididymis at the larger, superior portion of the epididymis called the head. The body is the narrow midportion of the epididymis, and the tail is the smaller, inferior portion. At its distal end, the tail of the epididymis continues as the ductus (vas) deferens (discussed shortly). The ductus epididymis would measure about 6 m (20 ft) in length if it were straightened out. It is lined with pseudostratified columnar epithelium and encircled by a layer of smooth mus- cle epididymis is the site of sperm maturation, the process by which sperm acquire motility and the ability to fertilize an ovum. This occurs over a period of about 14 days.

gastrointestinal (GI) tract, or alimentary canal

is a continuous tube that extends from the mouth to the anus through the thoracic and abdomi- nopelvic cavities. Organs of the gastrointestinal tract include the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The length of the GI tract is variable. It is about 5-7 meters (16.5-23 ft) in a living person when the muscles along the walls of GI tract organs are in a state of tonus (sus- tained contraction). It is longer in a cadaver (about 7-9 meters or 23-29.5 ft) because of the loss of muscle tone after death.

alveolus

is a cup- shaped outpouching lined by simple squamous epithelium and The respiratory membrane consists of a layer of type I and type II alveolar cells, an epithelial basement membrane, a capillary basement membrane, and the capillary endothelium.

Renal failure

is a decrease or cessation of glomerular filtration. In acute renal failure (ARF), the kidneys abruptly stop work- ing entirely (or almost entirely). The main feature of ARF is the suppression of urine flow, usually characterized either by oliguria (ol- i-GU ̄ -reˉ-a) (daily urine output between 50 mL and 250 mL), or anuria (an-U ̄ -reˉ-a) (daily urine output less than 50 mL). Causes include low blood volume (for example, due to hemorrhage), decreased cardiac output, damaged renal tubules, kidney stones, reactions to the dyes used to visualize blood vessels in angiograms, nonsteroidal anti- inflammatory drugs, some antibiotic drugs, and traumatic injury.

The oropharyngeal membrane

is a depression of fused ectoderm and endoderm on the sur- face of the embryo that separates the foregut from the stomodeum. The membrane ruptures during the fourth week of development, so that the foregut is continuous with the outside of the embryo through the oral cavity. Another depression consisting of ecto- derm, the proctodeum (prok-toˉ-DE ̄ -um), forms in the hindgut and goes on to develop into the anus. (See Figure 4.12d.) The cloa- cal membrane (kloˉ -Aˉ -kul) is a fused membrane of ectoderm and endoderm that separates the hindgut from the proctodeum. After the cloacal membrane ruptures during the seventh week, the hindgut forms a continuous tube from mouth to anus.

pharynx

is a funnel-shaped tube that extends from the internal nares to the esophagus posteriorly and the larynx anteriorly (see Figure 23.2b). The pharynx is composed of skeletal muscle and lined by mucous membrane. The nasopharynx functions only in respiration, but the oropharynx and laryngopharynx have both digestive and respiratory functions.

salivary gland

is a gland that releases a secretion called saliva into the oral cavity. Ordinarily, just enough saliva is secreted to keep the mucous membranes of the mouth and phar- ynx moist and to cleanse the mouth and teeth. When food enters the mouth, however, secretion of saliva increases to lubricate, dis- solve, and begin the chemical breakdown of the food.

fsh

is a gonadotropin, a glycoprotein polypeptide hormone. FSH is synthesized and secreted by the gonadotropic cells of the anterior pituitary gland,[1] and regulates the development, growth, pubertal maturation, and reproductive processes of the body. FSH and luteinizing hormone (LH) work together in the reproductive system.

breast

is a hemispheric projection of variable size anterior to the pectoralis major and serratus anterior muscles and attached to them by a layer of fascia composed of dense irregular connec- tive tissue (Figure 26.23). Each breast has one pigmented projection, the nipple, which has a series of closely spaced openings of ducts called lactiferous ducts (lak-TIF-er-us), where milk emerges. The circular pigmented area of skin surrounding the nipple is called the areola (a-RE ̄ -oˉ -la small space); it appears rough because it contains modified sebaceous (oil) glands. Strands of connective tissue called the suspensory liga- ments of the breast (Cooper's ligaments) run between the skin and fascia and support the breast. These ligaments become looser with age or with excessive strain, as occurs in long-term jogging or high- impact aerobics. Wearing a supportive bra can slow this process and help maintain the integrity of the suspensory ligaments.

Parathyroid hormone (PTH)

is a hormone secreted by the parathyroid glands that is important in bone remodeling, which is an ongoing process in which bone tissue is alternately resorbed and rebuilt over time. PTH is secreted in response to low blood serum calcium (Ca2+) levels. PTH indirectly stimulates osteoclast activity within bone marrow, in an effort to release more ionic calcium (Ca2+) into the blood to elevate serum calcium (Ca2+) levels. The bones act as a (metaphorical) "bank of calcium" from which the body can make "withdrawals" as needed to keep the amount of calcium in the blood at appropriate levels despite the ever-present challenges of metabolism, stress, and nutritional variations. PTH is "a key that unlocks the bank vault" to remove the calcium.

adh

is a hormone synthesized as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It then travels down the axon of that cell, which terminates in the posterior pituitary, and is released from vesicles into the circulation in response to extracellular fluid hypertonicity (hyperosmolality). AVP has two primary functions. First, it increases the amount of solute-free water reabsorbed back into the circulation from the filtrate in the kidney tubules (nephrons). Second, AVP constricts arterioles, which increases peripheral vascular resistance and raises arterial blood pressure.[6][7][8]

androgen

is a hormone that pro- motes the development of masculine characteristics. Testoster- one also promotes a man's libido

mature (graafian) follicle

is a large, fluid-filled follicle that is ready to rupture and expel its secondary oocyte, a process known as ovulation (ov-u ̄-LAˉ-shun).

epiglottis

is a large, leaf-shaped piece of elastic cartilage that is covered with epithelium (Fig- ure 23.3b, c, h). The "stem" of the epiglottis is the tapered inferior portion that is attached to the anterior rim of the thyroid cartilage. The broad superior "leaf" portion of the epiglottis is unattached and is free to move up and down like a trap door. During swallow- ing, the pharynx and larynx rise. Elevation of the pharynx widens it to receive food or drink; elevation of the larynx causes the epiglottis to move down and form a lid over the opening into the larynx, clos- ing it off. The narrowed passageway through the larynx is called the glottis. The glottis consists of a pair of folds of mucous membrane, the vocal folds in the larynx, and the space between them called the rima glottidis (RI ̄-ma GLOT-ti-dis; Figure 23.3h). The closing of the larynx during swallowing routes liquids and foods into the es- ophagus and keeps them out of the larynx and airways. When small particles of dust, smoke, food, or liquids pass into the larynx, a cough reflex occurs, usually expelling the material. epithelium consisting of ciliated columnar cells, goblet cells, and basal cells. The mucus secreted by these cells helps trap dust not removed in the upper passages. In contrast to the action of the cilia in the upper respiratory tract, which move mucus and trapped particles down toward the pharynx, the cilia in the lower respira- tory tract move the mucus up toward the pharynx.

tunica media

is a layer composed of smooth muscle and connective tissue. This layer displays the greatest var- iation among the different vessel types

Swallowing, or deglutition

is a mechanism that moves food from the mouth to the stomach. It is helped by saliva and mucus and involves the mouth, pharynx, and esophagus. Food that is swallowed passes from the mouth into the oropharynx and laryngophar- ynx before passing into the esophagus. Muscular contractions of the oropharynx and laryngopharynx help propel food into the esophagus and then into the stomach.

Semen

is a mixture of sperm and seminal fluid, a liquid that consists of the secretions of the seminiferous tubules, semi- nal vesicles, prostate, and bulbourethral glands. The volume of semen in a typical ejaculation is 2.5-5 mL, with a sperm count (concentration) of 50-150 million sperm/mL. A male whose sperm count falls below 20 million/mL is likely to be infertile. The very large number is required for successful fertilization be- cause only a tiny fraction ever reach the secondary oocyte. Despite the slight acidity of prostatic fluid, semen has a slightly alkaline pH of 7.2-7.7 due to the higher pH and larger volume of fluid from the seminal vesicles. The prostatic secretion gives semen a milky appearance, and fluids from the seminal vesicles and bulbourethral glands give it a sticky consistency. Seminal fluid provides sperm with a transportation medium, nutrients, and protection from the hostile acidic environment of the male's urethra and the female's vagina. Once ejaculated, liquid semen coagulates within 5 minutes due to the presence of clotting proteins from the seminal vesicles. The functional role of semen coagulation is not known, but the proteins involved are different from those that cause blood co- agulation. After about 10-20 minutes, semen reliquefies because prostate-specific antigen (PSA) and other proteolytic enzymes produced by the prostate break down the clot. Abnormal or de- layed liquefaction of clotted semen may cause complete or par- tial immobilization of sperm, thereby inhibiting their movement through the cervix of the uterus. After passing through the uterus to the uterine tube, the sperm are affected by secretions of the uterine tube in a process called capacitation (see Section 26.2).

gallbladder

is a pear-shaped sac that is lo- cated on the inferior surface of the liver. It is 7-10 cm (3-4 in.) long and part of it typically hangs below the anterior inferior margin of the liver

oxytocin

is a peptide hormone and neuropeptide. Oxytocin is normally produced by the paraventricular nucleus of the hypothalamus and released by the posterior pituitary.[3] It plays a role in social bonding, sexual reproduction in both sexes, and during and after childbirth.[4] Oxytocin is released into the bloodstream as a hormone in response to stretching of the cervix and uterus during labor and with stimulation of the nipples from breastfeeding.[5] This helps with birth, bonding with the baby, and milk production.[5][6]

inhibin

is a protein secreted by granulosa (female) and Sertoli (male) cells in response to FSH, and its major action is the negative feedback control of pituitary FSH secretion (ref 1). It is found in blood plasma, although difficult to detect until recently.

ovarian cortex

is a region just deep to the tunica albug- inea. It consists of ovarian follicles (described shortly) sur- rounded by dense irregular connective tissue that contains collagen fibers and fibroblast-like cells called stromal cells.

gnrh

is a releasing hormone responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. GnRH is a tropic peptide hormone synthesized and released from GnRH neurons within the hypothalamus.

cricoid cartilage

is a ring of hyaline cartilage that forms the inferior wall of the larynx. It is attached to the first ring of cartilage of the trachea by the cricotracheal liga- ment (kri ̄ -ko ̄-TRA ̄-ke ̄-al). The thyroid cartilage is connected to the cricoid cartilage by the cricothyroid ligament. The cricoid cartilage is the landmark for making an emergency airway called a tracheotomy. ̄

urethra

is a small tube leading from the internal urethral orifice in the floor of the urinary bladder to the exte- rior of the body

spermatic cord

is a supporting structure of the male re- productive system that ascends out of the scrotum It consists of the ductus deferens as it ascends through the scrotum, the testicular artery, both somatic and autonomic nerves, veins that drain the testes and carry testosterone into the circulation (the pampiniform plexus), lymphatic vessels, the cremaster muscle and fascial covering.

penis

is a supporting structure of the male reproductive system that contains the urethra and is a passage- way for the ejaculation of semen and the excretion of urine (Fig- ure 26.10). It is cylindrical in shape and consists of a body, glans penis, and a root (see Figure 26.1). The body of the penis is composed of three cylindrical masses of tissue, each surrounded by fibrous tissue called the tunica albuginea (al-bu ̄ -JIN-eˉ -a; Figure 26.10). The two dorsolateral masses of the body of the penis are called the corpora cavernosa penis (corpora main bodies; cavernosa hollow; singular is corpus cavernosum penis).

endothelium

is a thin layer of flattened cells that lines the inner surface of the entire cardiovascular system

submucosa

is a thin meshwork of collagenous fibers, nerves, and blood vessels. It consists of areolar connective tissue that binds the mucosa to the middle layer, the muscularis. The submucosa is highly vascular and contains the submucosal plexus, or plexus of Meissner (MI ̄S-ner), a portion of the autonomic nervous system (ANS) called the enteric nervous system (ENS) (see Section 19.5). The ENS is the "brain of the gut" and consists of approx- imately 100 million neurons in two main enteric plexuses that extend the entire length of the GI tract. The submucosal plexus (plexus of Meissner) contains sensory and motor enteric neurons, plus parasympathetic and sympathetic postganglionic fibers that innervate the mucosa and submucosa. It regulates movements of the mucosa and vasoconstriction of blood vessels. Because it also innervates secretory cells of mucosal glands, the submucosal plexus is important in controlling secretions of the GI tract. The submucosa may also contain glands and lymphatic tissue.

internal elastic lamina

is a thin sheet of elastic fibers with a variable number of window-like openings that give it the look of Swiss cheese. These openings facilitate diffusion of materials through the tunica interna to the thicker tunica media.

vagina

is a tubular, fibromuscular canal lined with mucous membrane that extends from the exterior of the body to the uterine cervix (see Figures 26.11 and 26.16). It is about 10 cm (4 in.) long, and serves as the receptacle for the penis dur- ing sexual intercourse, the outlet for menstrual flow, and the pas- sageway for childbirth. Situated posterior to the urinary bladder and urethra and anterior to the rectum, the vagina is directed superiorly and posteriorly, to attach to the cervix of the uterus. A recess called the fornix ( arch or vault) surrounds the vaginal attachment to the cervix (see Figure 26.16a). When properly in- serted, a contraceptive diaphragm rests in the fornix, where it is held in place as it covers the cervix.

vascular (venous) sinus

is a vein with a thin endothelial wall that has no smooth muscle to alter its diameter.

tunica albuginea

is a whitish capsule of dense, irregular connective tissue immediately deep to the ger- minal epithelium.

ejaculatory duct

is about 2 cm (1 in.) long and is formed by the union of the duct from the seminal vesicle and the ampulla of the ductus deferens (see Figure 26.9). The short ejaculatory ducts form just superior to the base (superior portion) of the prostate and pass inferiorly and anteriorly through the prostate. They terminate in the pro- static urethra, where they eject sperm and seminal vesicle secre- tions just before the release of semen from the urethra to the exterior.

head

is about 4-5 m long. It contains a nucleus that has highly con- densed haploid chromosomes (23). Covering the anterior two- thirds of the nucleus is the acrosome (AK-roˉ -soˉ m; acro- atop; some body), a caplike vesicle filled with enzymes that help a sperm to penetrate a secondary oocyte to bring about fertiliza- tion. Among the enzymes are hyaluronidase and proteases.

tongue

is an accessory digestive organ composed of skel- etal muscle covered with mucous membrane. Together with its associated muscles, it forms the floor of the oral cavity. The tongue is divided into symmetrical lateral halves by a median sep- tum that extends its entire length, and it is attached to the hyoid

lamina propria

is an areolar connective tissue layer containing many blood and lymphatic vessels that carry the nutrients absorbed by the GI tract back to the heart. This layer supports the epithelium and binds it to the muscularis mucosae (discussed next). The lamina propria also contains most of the cells of the mucosa-associated lymphatic tissue (MALT). These prominent lymphatic nodules contain immune system cells that protect against disease. MALT is present all along the GI tract, especially in the tonsils, small intestine, appendix, and large intestine, and it contains about as many immune cells as are present in all the rest of the body. The lymphocytes and macrophages in MALT mount immune responses against mi- crobes, such as bacteria, that may penetrate the epithelium.

The sequence of fluid flow is

is blood capillaries (blood) S interstitial spaces (interstitial fluid) S lymphatic capillaries (lymph) S lymphatic vessels (lymph) S lymphatic ducts (lymph) S junction of internal jugular and subclavian veins (blood).

The middle layer, the muscularis

is composed of an inner, thick, circular ring of smooth muscle and an outer, thin region of longitudinal smooth muscle. Peristaltic contractions of the muscularis and the ciliary action of the mucosa help move the oocyte or fertilized ovum toward the uterus.

muscularis

is composed of inner longitudinal and outer circular layers of smooth muscle fibers, an arrangement opposite that of the gastrointestinal tract, which contains inner circular and outer longitudinal layers.

The cortex

is composed of large numbers of T cells and scattered dendritic cells, epithelial cells, and macrophages. Immature T cells migrate from red bone marrow to the cortex of the thymus, where they prolifer- ate and begin to mature.

The mucosa of the vagina

is continuous with that of the uterus. Histologically, it consists of nonkeratinized stratified sq- uamous epithelium and lamina propria (areolar connective tissue) Dendritic cells in the mucosa are antigen-presenting cells. Unfortunately, they also participate in the transmission of viruses—for example, HIV (the virus that causes AIDS)—to a female during intercourse with an infected male. The mucosa of the vagina contains large stores of glyco- gen, the decomposition of which produces organic acids. The resulting acidic environment retards microbial growth, but it is also harmful to sperm. Alkaline components of semen, mainly from the seminal vesicles, raise the pH of fluid in the vagina and increase viability of the sperm.

salivation

is controlled by the nervous system. Normally, parasympathetic stimulation promotes continuous secretion of a moderate amount of saliva, which keeps the mucous membranes moist and lubri- cates the movements of the tongue and lips during speech. The saliva is then swallowed and helps moisten the esophagus. Even- tually, most components of saliva are reabsorbed, which prevents fluid loss. Sympathetic stimulation dominates during stress, re- sulting in dryness of the mouth. Dehydration also causes dryness of the mouth. The salivary glands stop secreting saliva to con- serve water, and the resulting dryness contributes to the sensation of thirst. Drinking will then not only restore the homeostasis of body water but also moisten the mouth.

premature ejaculation

is ejaculation that occurs too early, for example, during foreplay or upon or shortly after penetra- tion. It is usually caused by anxiety, other psychological causes, or an unusually sensitive foreskin or glans penis. For most males, premature ejaculation can be overcome by various mechanical techniques (such as squeezing the penis between the glans pe- nis and shaft as ejaculation approaches), behavioral therapy, or medication.

mesentery

is fan-shaped and binds the jejunum and ileum of the small intestine to the posterior abdominal wall (Fig- ure 24.3a, d). This is the largest peritoneal fold and is typically laden with fat, which contributes extensively to a large abdomen in obese individuals. It extends from the posterior abdominal wall to wrap around almost the entire length of the small intestine and then returns to its origin, forming a double-layered structure. Between the two layers are blood vessels (branches and tributar- ies of the superior mesenteric artery and vein), lymphatic vessels, and lymph nodes associated with the jejunum and ileum. In order to fit the entire small intestine with its large mesentery into the abdominal cavity, the intestine and mesentery are folded together like a fan to make them more compact.

oral or buccal cavity

is formed by the cheeks, hard and soft palates, and tongue

The arterial blood supply of the small intestine

is from the superior mesenteric artery and the gastroduodenal artery, which arises from the hepatic artery of the celiac trunk. Blood is re- turned by way of the superior mesenteric vein, which anastomo- ses with the splenic vein to form the hepatic portal vein.

accessory duct

leads from the pancreas and empties into the duodenum about 2.5 cm (1 in.) superior to the hepatopancreatic ampulla

endometrium

is highly vascularized and has three components: (1) An innermost layer composed of simple columnar epithelium (cili- ated and secretory cells) lines the lumen. (2) An underlying endometrial stroma is a very thick region of lamina propria (are- olar connective tissue). (3) Endometrial (uterine) glands develop as invaginations of the luminal epithelium and extend almost to the myometrium. The endometrium is divided into two layers. The stratum functionalis ( functional layer) lines the uterine cavity and sloughs off during menstruation as a result of declin- ing levels of progesterone from the ovaries. The deeper layer, the stratum basalis ( basal layer), is permanent and gives rise to a new stratum functionalis after each menstruation.

embryoblast

is located in- ternally and eventually develops into the embryo and some of the extraembryonic membranes.

White pulp

is lymphatic tissue, consist- ing mostly of lymphocytes and macrophages arranged around branches of the splenic artery called central arteries.

medullary respiratory center

is made up of two collections of neurons called the dorsal respiratory group (DRG) formerly known as the inspiratory area, and the ventral respiratory group (VRG), formerly called the expiratory area (Figure 23.13a). During normal quiet breathing, neurons of the DRG generate impulses to the diaphragm via the phrenic nerves and the external intercostal muscles via the intercostal nerves (Figure 23.13a, b and Figure 23.14a). These impulses are released in bursts, which begin weakly, increase in strength for about two seconds, and then stop altogether. When the nerve impulses reach the diaphragm and ex- ternal intercostal muscles, the diaphragm contracts, the external intercostal muscles contract during their most active phase, and inhalation occurs. When the DRG becomes inactive after two sec- onds, the diaphragm relaxes and the external intercostal muscles become less active and relax for about three seconds, allowing pas- sive recoil of the lungs and thoracic wall. This results in exhala- tion. Then the cycle repeats itself. Even when all incoming nerve impulses to the DRG are cut or blocked, neurons in this area still rhythmically discharge impulses that cause inhalation. However, traumatic injury to both phrenic nerves causes paralysis of the dia- phragm and cessation of breathing. The neurons of the VRG do not participate in normal quiet inhalation. However, when forceful breathing is required, such as during exercise, playing a wind instrument, or at high altitudes, the VRG becomes activated as follows. During forceful inhalation (Figure 23.14b), nerve impulses from the DRG not only stimu- late the diaphragm and external intercostal muscles to contract, they also activate neurons of the VRG involved in forceful inhala- tion to send nerve impulses to the accessory muscles of inhalation (sternocleidomastoid, scalene, and pectoralis minor muscles). Contraction of these muscles results in forceful inhalation. During forceful exhalation (Figure 23.14b), the DRG is inac- tive along with the neurons of the VRG that result in forceful exhalation, but neurons of the VRG involved in forceful exhala- tion send nerve impulses to the accessory muscles of exhalation (internal intercostal, external oblique, internal oblique, trans- versus abdominis, and rectus abdominis muscles). Contraction of these muscles results in forceful exhalation. Also located in the VRG is a cluster of neurons called the pre- Bötzinger complex (BOT-zin-ger) that is believed to be important in the generation of the rhythm of breathing (Figure 23.13a). This rhythm generator, analogous to the cardiac conduction sys- tem of the heart, is composed of pacemaker cells that set the basic rhythm of breathing. The exact mechanism of the pacemaker cells is unknown and is the topic of much ongoing research. However, it is thought that the pacemaker cells provide input to the DRG, driving the rate at which DRG neurons fire nerve impulses.

Chemical digestion

is the breakdown of the large carbohydrate, lipid, protein, and nucleic acid molecules present in food into smaller molecules that can be absorbed (see next step). Digestive enzymes produced by the salivary glands, tongue, stomach, pancreas, and small intestine speed up these breakdown reactions. A few substances in food can be absorbed without chemical digestion, including amino acids, cholesterol, glucose, vitamins, minerals, and water.

perineum

is the diamond-shaped area medial to the thighs and buttocks of both males and females (Figure 26.22). It contains the external genitals and anus. The perineum is bounded anteriorly by the pubic symphysis, later- ally by the ischial tuberosities, and posteriorly by the coccyx. A transverse line drawn between the ischial tuberosities divides the perineum into an anterior urogenital triangle (u ̄ -roˉ-JEN-i-tal) that encloses the urethral (uro-) and vaginal (-genital) orifices and a posterior anal triangle that contains the anus.

Respiration

is the exchange of gases between the atmosphere, blood, and body cells.

Thymosin

is the hormone of the thymus, and it stimulates the development of disease-fighting T cells.

liver

is the largest internal organ and heaviest gland of the body, weighing about 1.4 kg (about 3 lb) in an average adult. Of the organs of the body, it is second in size only to the skin. The liver is inferior to the diaphragm and occupies most of the right hypochondriac and part of the epigastric regions of the abdomi- nopelvic cavity

peritoneum

is the largest serous membrane of the body; it consists of a layer of simple sq- uamous epithelium (mesothelium) with an underlying supporting layer of connective tissue. The peritoneum is divided into the pa- rietal peritoneum, which lines the wall of the abdominal cavity, and the visceral peritoneum or serosa, which as you just learned covers some of the organs in the cavity

spleen

is the largest single mass of lymphatic tissue in the body. It is a soft, encapsulated organ of variable size, but on average, it fits in a person's open hand and measures about 12 cm (5 in.) in length (Figure 15.7a). It is located in the left hypochondriac region between the stomach and diaphragm. The superior surface of the spleen is smooth and convex and conforms to the concave surface of the diaphragm.

spermiogenesi

is the maturation of haploid spermatids into sperm. Because no cell division occurs in spermiogenesis, each spermatid develops into a single sperm cell. During this process, spherical spermatids transform into elongated, slender sperm. An acrosome (described shortly) forms atop the condensing and elongating nucleus, a flagellum develops, and mitochondria mul- tiply. Sustentacular cells dispose of the excess cytoplasm that is sloughed off during this process.

trophoblast

is the outer superficial layer of cells that forms the sphere-like wall of the blastocyst.

Puberty

is the period when secondary sexual characteristics begin to develop and the po- tential for sexual reproduction is reached. The onset of puberty is marked by pulses or bursts of LH and FSH secretion, each trig- gered by a pulse of GnRH. Most pulses occur during sleep. As puberty advances, the hormone pulses occur during the day as well as at night. The pulses increase in frequency during a 3- to 4-year period until the adult pattern is established. The stimuli that cause the GnRH pulses are still unclear, but a role for the hormone lep- tin is starting to unfold. Just before puberty, leptin levels rise in proportion to adipose tissue mass. Interestingly, leptin receptors are present in both the hypothalamus and anterior pituitary. Mice that lack a functional leptin gene from birth are sterile and remain in a prepubertal state. Giving leptin to such mice elicits secretion of gonadotropins, and they become fertile. Leptin may signal the hypothalamus that long-term energy stores (triglycerides in adi- pose tissue) are adequate for reproductive functions to begin.

estrogen

is the primary female sex hormone as well as a medication. It is responsible for the development and regulation of the female reproductive system and secondary sex characteristics. Estrogen may also refer to any substance, natural or synthetic, that mimics the effects of the natural hormone.[1]

oral cavity proper

is the space that extends from the gums and teeth to the fauces (FAW-seˉs passages), the opening between the oral cavity and the oropharynx.

cavity of the larynx

is the space that extends from the laryngeal entrance to the inferior bor- der of the cricoid cartilage. The portion of the cavity of the larynx above the vestibular folds is called the laryngeal vestibule. The portion of the cavity of the larynx below the vocal folds is called the infraglottic cavity

Preovulatory Phase

is the time be- tween the end of menstruation and ovulation. The preovulatory phase of the cycle is more variable in length than the other phases and accounts for most of the difference when cycles are shorter or longer than 28 days. It lasts from days 6 to 13 in a 28-day cycle.

lobules

it ex- tends inward, forming septa that divide each testis into a series of internal compartments

hcg what he said

it is secreted from the chorion - the outer layer of the placenta (the inner one is the amnion). It starts being detectable after about a week after implantation and is an indicator used in home pregnancy tests. The same hormone is secreted from the ovary in cases of tumors or other disease states (giving false positives in pregnancy tests). It is very similar to luteinizing hormone and can bind to the same receptors. Hence it acts on the corpus luteum in the ovary, stopping it from degenerating and enhancing its secretion of the hormone progesterone (think of this as pro-gestation) which helps in enriching the endometrium around the implanted embryo. There are several other

nasopharynx

lies posterior to the nasal cavity and extends to the plane of the soft palate. The soft palate, which forms the posterior portion of the roof of the mouth, is an arch-shaped muscular partition be- tween the nasopharynx and oropharynx that is covered by mucous membrane. There are five openings in the wall of the nasophar- ynx: two internal nares, two openings that lead into the auditory (pharyngotympanic) tubes (commonly known as the eustachian tubes), and the single opening into the oropharynx. The posterior wall also contains the pharyngeal tonsil(fa-RIN-jeˉ-al)oradenoid. Through the internal nares, the nasopharynx receives air from the nasal cavity and receives packages of dust-laden mucus. The nasopharynx is lined with pseudostratified ciliated columnar epi- thelium, and the cilia move the mucus down toward the most in- ferior part of the pharynx. The nasopharynx also exchanges small amounts of air with the auditory tubes to equalize air pressure between the middle ear and the atmosphere.

oropharynx

lies posterior to the oral cavity and extends from the soft palate inferiorly to the level of the hyoid bone. In addition to commu- nicating upward with the nasopharynx and downward with the laryngopharynx, it has an anterior opening, the fauces (FAW- seˉz throat), the opening from the mouth. This portion of the pharynx has both respiratory and digestive functions because it is a common passageway for air, food, and drink. Because the oropharynx is subject to abrasion by food particles, it is lined with nonkeratinized stratified squamous epithelium. Two pairs of tonsils, the palatine tonsils and lingual tonsils, are found in the oropharynx.

esophagus

long collapsible muscular tube that lies posterior to the trachea. It begins at the inferior end of the laryngopharynx, passes through the inferior aspect of the neck, enters the mediastinum and de- scends anterior to the vertebral column, pierces the diaphragm through an opening called the esophageal hiatus (e-sof-a-JE ̄ -al h ̄ı-Aˉ-tus), and ends in the superior portion of the stomach (see Figure 24.1). Sometimes, a portion of the stomach protrudes above the diaphragm through the esophageal hiatus.

stereocilia

long, branching microvilli that increase surface area for the reabsorption of degenerated sperm. Connective tissue around the muscle layer attaches the loops of the ductus epididymis to one another and carries blood vessels and nerves.

Saliva

lubricates and dissolves foods and begins the chemical breakdown of carbohydrates and lipids. ranges from 1000 to 1500 mL (1 to 1.6 qt). Chemically, saliva is 99.5 percent water and 0.5 percent solutes and has a slightly acidic pH (6.35 to 6.85). The solute portion includes mucus, an enzyme that destroys bacteria (lysozyme), the digestive enzymes salivary amylase and lingual lipase, and traces of salts, proteins, and other organic compounds. Salivary amylase (AM-i-la ̄ s) plays a minor role in the breakdown of starch in the mouth into mal- tose, maltotriose, and 1-dextrins. ˉ

Lymphatic vessels develop from

lymph sacs; lymph sacs arise from developing veins, which are derived from mesoderm. The first lymph sacs to appear are the paired jugular lymph sacs at the junction of the internal jugular and subclavian veins

lymphatic vessels begin as

lymphatic capillaries. These capil- laries are closed at one end and located in the spaces between cells (Figure 15.2). Just as blood capillaries converge to form venules and then veins, lymphatic capillaries unite to form larger lymphatic vessels (see Figure 15.1), which resemble small veins in structure but have thinner walls and more valves. At in- tervals along the lymphatic vessels, lymph flows through lymph nodes, encapsulated masses of B cells and T cells. In the skin, lymphatic vessels lie in the subcutaneous tissue and generally follow the same route as veins; lymphatic vessels of the viscera generally follow arteries, forming plexuses (networks) around them. Tissues that lack lymphatic capillaries include avascular tissues (such as cartilage, the epidermis, and the cornea of the eye), the central nervous system, portions of the spleen, and red bone marrow.

The secondary follicle eventually becomes larger, turning into

mature (graafian) follicle (Figure 26.14d). While in this follicle, and just before ovulation, the diploid primary oocyte completes meiosis I, producing two haploid (n) cells of unequal size—each with 23 chromosomes (Figure 26.15). The smaller cell produced by meiosis I, called the first polar body, is essentially a packet of discarded nuclear material. The larger cell, known as the secondary oocyte, receives most of the cytoplasm. Once a secondary oocyte is formed, it begins meiosis II but then stops in metaphase. The mature (graafian) follicle soon ruptures and releases its secondary oocyte, a process known as ovulation.

Postovulatory Phase

of the female reproductive cycle is the time between ovulation and onset of the next menses. In dura- tion, it is the most constant part of the female reproductive cycle. It lasts for 14 days in a 28-day cycle, from day 15 to day 28 (see Figure 26.25). The female reproductive cycle can be disrupted by many fac- tors, including weight loss, low body weight, disordered eating, and vigorous physical activity. The observation that three condi- tions—disordered eating, amenorrhea, and osteoporosis—often occur together in female athletes led researchers to coin the term female athlete triad. Many athletes experience intense pressure from coaches, par- ents, peers, and themselves to lose weight to improve perform- ance. Hence, they may develop disordered eating behaviors and engage in other harmful weight-loss practices in a struggle to maintain a very low body weight. Amenorrhea (a ̄ -men -oˉ -RE ̄ -a; a- without; men- month; rrhea a flow) is the absence of men- struation. The most common causes of amenorrhea are pregnancy and menopause. In female athletes, amenorrhea results from re- duced secretion of gonadotropin-releasing hormone, which de- creases the release of LH and FSH. As a result, ovarian follicles fail to develop, ovulation does not occur, synthesis of estrogens and progesterone wanes, and monthly menstrual bleeding ceases. Most cases of the female athlete triad occur in young women with very low amounts of body fat. Low levels of the hormone leptin, secreted by adipose cells, may be a contributing factor. Because estrogens help bones retain calcium and other miner- als, chronically low levels of estrogens are associated with loss of bone mineral density. The female athlete triad causes "old bones in young women." In one study, amenorrheic runners in their twenties had low bone mineral densities, similar to those of post- menopausal women 50 to 70 years old! Short periods of amen- orrhea in young athletes may cause no lasting harm. However, long-term cessation of the reproductive cycle may be accompa- nied by a loss of bone mass, and adolescent athletes may fail to achieve an adequate bone mass; both of these situations can lead to premature osteoporosis and irreversible bone damage.

lamina propria

of the male urethra is areolar con- nective tissue with elastic fibers and a plexus of veins.

muscularis

of the mouth, pharynx, and superior and mid- dle parts of the esophagus contains skeletal muscle that produces voluntary swallowing. Skeletal muscle also forms the external anal sphincter, which permits voluntary control of defecation. Throughout the rest of the tract, the muscularis consists of smooth muscle that is generally found in two sheets: an inner sheet of circular fibers and an outer sheet of longitudinal fibers. Involun- tary contractions of the smooth muscles assist in the mechanical breakdown of food, mix it with digestive secretions, and propel it along the tract. The muscularis also contains the second major plexus of the enteric nervous system—the myenteric plexus (my- muscle), or plexus of Auerbach (OW-er-bak), which contains en- teric neurons, parasympathetic ganglia and postganglionic fibers, and sympathetic postganglionic fibers that are vasomotor to the blood vessels of this layer. This plexus mostly controls GI tract motility (movement), in particular the frequency and strength of the contractions of the muscularis.

oral vestibule

of the oral cavity is the space bounded externally by the cheeks and lips and internally by the gums and teeth.

mucosa

of the trachea consists of an epithelial layer of pseu- dostratified ciliated columnar epithelium and an underlying layer of lamina propria that contains elastic and reticular fibers. The epithelium consists of ciliated columnar cells and goblet cells that reach the luminal surface, plus basal cells that do not (see Table 3.1E). The epithelium provides the same protection against dust as the membrane lining the nasal cavity and larynx.

ampulla

of the uter- ine tube is the widest, longest portion, making up about the lateral two-thirds of its length.

isthmus

of the uterine tube is the more medial, short, narrow, thick-walled portion that joins the uterus.

Nephroptosis

or floating kid- ney, is an inferior displacement or dropping of the kidney. It occurs when the kidney slips from its normal position because it is not securely held in place by adjacent organs or its covering of fat. Nephroptosis develops most often in very thin people whose adipose capsule or renal fascia is deficient. It is dangerous because the ureter may kink and block urine flow. The resulting backup of urine puts pressure on the kidney, which damages the tissue. Twisting of the ureter also causes pain. Nephroptosis is very common; about one in four people has some degree of weakening of the fibrous bands that hold the kidney in place. It is 10 times more common in females than males. Because it happens during life, it is very easy to distinguish from congenital anomalies.

mucosa

or inner lining of the GI tract, is a mucous mem- brane. It is composed of (1) a layer of epithelium in direct contact with the contents of the GI tract, (2) areolar connective tissue, and (3) a thin layer of smooth muscle (muscularis mucosae).

perimetrium

or serosa—is part of the peritoneum; it is composed of simple squamous epithelium and a thin layer of areolar connective tissue. Laterally, the peritoneum becomes the broad ligament. Anteriorly, the peritoneum covers the urinary bladder and forms a shallow pouch, the vesicouterine pouch (ves -i-koˉ -U ̄ -ter-in; vesico- bladder; see Figure 26.11) between the urinary bladder and the uterus. Posteriorly, the peritoneum covers the rectum and forms a deep pouch between the uterus and the rectum, the rectouterine pouch (rek-toˉ-U ̄-ter-in; recto- rectum) or pouch of Douglas—the most inferior point in the peritoneal cavity.

pharynx

or throat, is a funnel-shaped tube about 13 cm (5 in.) long that starts at the internal nares and extends to the level of the cricoid cartilage, the most inferior cartilage of the larynx (voice box) (Figure 23.2). The pharynx lies just posterior to the nasal and oral cavities, superior to the larynx and esophagus, and just anterior to the cervical vertebrae. Its wall is composed of skeletal muscles and is lined with a mucous membrane. Relaxed skeletal muscles help keep the pharynx patent. Contraction of the skeletal muscles assists in deglutition (swallowing). The pharynx functions as a passageway for air and food, provides a resonat- ing chamber for speech sounds, and houses the tonsils, which participate in immunological reactions against foreign invaders.

larynx

or voice box, is a short passageway that connects the laryngopharynx with the trachea. It lies in the midline of the neck anterior to the fourth through sixth cervical vertebrae (C4-C6). The wall of the larynx is composed of nine pieces of cartilage (Figure 23.3). Three occur singly (thyroid cartilage, epiglottis, and cricoid cartilage), and three occur in pairs (arytenoid, cuneiform, and corniculate cartilages). Of the paired cartilages, the arytenoid cartilages are the most important because they influence the posi- tions and tensions of the vocal folds (true vocal cords). The extrin- sic muscles of the larynx connect the cartilages to other structures in the throat; the intrinsic muscles connect the cartilages to each other

intrinsic muscles of the tongue

originate in and insert into connective tissue within the tongue and alter the shape and size of the tongue for speech and swallowing. The intrinsic muscles include the longitudinalis superior, longitudinalis inferior, transver- sus linguae, and verticalis linguae muscles.

palate

palate is a wall or septum that separates the oral cavity from the nasal cavity, and forms the roof of the mouth. This im- portant structure makes it possible to chew and breathe at the same time. The hard palate—the anterior two-thirds of the palate—is formed by the maxillae and palatine bones and is covered by a mucous membrane. The soft palate, which forms the posterior portion of the roof of the mouth, is an arch-shaped muscular par- tition between the oropharynx and nasopharynx that is lined with mucous membrane.

Upon sexual stimulation

parasympathetic fibers from the sacral portion of the spinal cord initiate and maintain an erection, the enlargement and stiffening of the penis. The parasympathetic fibers produce and release and cause local production of nitric oxide (NO). The NO causes smooth muscle in the walls of arterioles supplying erectile tissue to relax, which allows these blood vessels to dilate. This in turn causes large amounts of blood to enter the erectile tissue of the penis. NO also causes the smooth muscle within the erectile tissue to relax, resulting in widening of the blood sinuses. The combination of increased blood flow and widening of the blood sinuses results in an erection. Expansion of the blood sinuses also compresses the veins that drain the penis; the slowing of blood outflow helps to maintain the erection.

Muscular contractions in the wall of the GI tract

physically break down the food by churning it, and propel the food along the tract, from the esophagus to the anus. The contractions also help to dissolve foods by mixing them with fluids secreted into the tract. Enzymes secreted by accessory digestive organs and cells that line the tract break down the food chemically.

hCG

primitive intersti- tal (Leydig) cells in the testes begin to secrete the androgen test- osterone during the eighth week. Testosterone then stimulates development of the mesonephric duct on each side into the epidi- dymis, ductus (vas) deferens, ejaculatory duct, and seminal vesicle. The testes connect to the mesonephric duct through a series of tubules that eventually become the seminiferous tubules. The prostate and bulbourethral glands are endodermal outgrowths of the urethra.

papillae

projections of the lamina propria covered with stratified squamous epithelium

The mucosa of the ductus defer- ens consists of

pseudostratified columnar epithelium and lamina propria (made up of areolar connective tissue).

The lungs receive blood via two sets of arteries:

pulmonary arter- ies and bronchial arteries. Deoxygenated blood passes through the pulmonary trunk, which divides into a left pulmonary artery that enters the left lung and a right pulmonary artery that en- ters the right lung. Return of the oxygenated blood to the heart occurs by way of the four pulmonary veins, which drain into the left atrium (see Figure 14.16). A unique feature of pulmonary blood vessels is their constriction in response to localized hypoxia (low O2 level). In all other body tissues, hypoxia causes dilation of blood vessels, which serves to increase blood flow. In the lungs, however, blood vessels constrict in response to hypoxia, divert- ing deoxygenated blood from poorly ventilated areas to well- ventilated regions of the lungs for more efficient gas exchange. Bronchial arteries, which branch from the aorta, deliver oxy- genated blood to the lungs. This blood mainly passes to the mus- cular walls of the bronchi and bronchioles. Connections do exist between branches of the bronchial arteries and branches of the pulmonary arteries; most blood returns to the heart via pulmo- nary veins. Some blood, however, drains into bronchial veins, which are tributaries of the azygos system (see Exhibit 14.J), and returns to the heart via the superior vena cava.

Chronic renal failure (CRF)

refers to a progressive and usually irreversible decline in glomerular filtration rate (GFR). CRF may re- sult from chronic glomerulonephritis, pyelonephritis, polycystic kid- ney disease, or traumatic loss of kidney tissue. The final stage, called end-stage renal failure, occurs when about 90 percent of the ne- phrons have been lost. At this stage, GFR diminishes to 10-15 percent of normal, oliguria is present, and blood levels of nitrogen-containing wastes and creatinine increase further. People with end-stage renal failure need dialysis therapy and are possible candidates for a kidney transplant operation. If a person's kidneys are so impaired by disease or injury that they are unable to function adequately, then blood must be cleansed arti cially by dialysis (dı ̄-AL-i-sis), which utilizes the same methods as kidney ltration: the separation of large solutes from smaller ones through use of a selectively permeable membrane. The leading cause of renal failure is diabetes. One method of dialysis is the arti cial kidney machine, which performs hemodialysis (heˉ - moˉ -dı ̄ -AL-i-sis; hemo- blood); it directly lters the patient's blood. As blood ows through tubing made of selectively permeable dialysis membrane, waste products diffuse from the blood into a dialysis solu- tion surrounding the membrane. The dialysis solution is continuously replaced to maintain favorable concentration gradients for diffusion of solutes into and out of the blood. After passing through the dialy- sis tubing, the cleansed blood ows back into the body. As a general rule, most affected people require 6-12 hours on dialysis each week (roughly every other day).

tachycardia

refers to a rapid heart rate (over 100 beats per minute)

Bradycardia

refers to a slow heart rate (below 50 beats per minute)

varicocele

refers to a swelling in the scrotum due to varicosities in the veins that drain the testes. It usually disappears when the person lies down, and typically does not require treatment.

Birth control

refers to restricting the number of children by vari- ous methods designed to control fertility and prevent conception. No single, ideal method of birth control exists. The only method of preventing pregnancy that is 100 percent reliable is complete abstinence, the avoidance of sexual intercourse. Several other methods are available, including surgical sterilization, hormonal methods, intrauterine devices, spermicides, barrier methods, and periodic abstinence. Each has its advantages and disadvantages. Table 26.3 provides the failure rates for various methods of birth control. Although it is not a form of birth control, in this sec- tion we will also discuss abortion, the premature expulsion of the products of conception from the uterus. contain hormones designed to prevent pregnancy. Some, called combined oral contraceptives (COCs), con- tain both progestin (hormone with actions similar to progester- one) and estrogens. The primary action of COCs is to inhibit ovulation by suppressing the gonadotropins FSH and LH. The low levels of FSH and LH usually prevent the development of a dominant follicle in the ovary. As a result, levels of estrogens do not rise, the midcycle LH surge does not occur, and ovulation does not take place. Even if ovulation does occur, as it does in some cases, COCs may also block implantation in the uterus and inhibit the transport of ova and sperm in the uterine tubes. Progestins thicken cervical mucus and make it more difficult for sperm to enter the uterus. Progestin-only pills thicken cervical mucus and may block implantation in the uterus but they do not consistently inhibit ovulation.

vulva or pudendum

refers to the external genitals of the female

diastole

relax

respiratory system

respiratory system consists of the nose, nasal cavity, phar- ynx (throat), larynx (voice box), trachea (windpipe), bronchi, and lungs.

In addition, the granulosa cells begin to

secrete follicular fluid, which builds up in a cavity called the antrum in the center of the secondary follicle. The inner- most layer of granulosa cells becomes firmly attached to the zona pellucida and is now called the corona radiata (corona crown; radiata radiation)

Paneth cells

secrete lysozyme, a bactericidal enzyme, and are capable of phagocytosis. Paneth cells may have a role in regulating the mi- crobial population in the small intestine.

Goblet cells

secrete mucus. The small intestinal mu- cosa contains many deep crevices lined with glandular epithe- lium. Cells lining the ̄ crevices form the intestinal glands or crypts of Lieberkühn (LE -ber-keˉ n) and secrete intestinal juice (to be discussed shortly). In addition to absorptive cells and goblet cells, the intestinal glands also contain enteroendocrine cells and paneth cells.

pepsin

secreted by chief cells in an inactive form called pepsinogen. Pep- sin breaks certain peptide bonds between the amino acids making up proteins. Thus, a protein chain of many amino acids is broken down into smaller fragments called peptides. Pepsin also brings about the clumping and digestion of milk proteins.

lingual lipase

secreted by lingual glands in the tongue, in the acid environment of the stomach

Gonadotropin-releasing hormone (GnRH)

secreted by the hypothalamus controls the events of the female reproduc- tive cycle (Figure 26.25). GnRH stimulates the release of follicle- stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary.

rugae

series of transverse folds

uterus

serves as part of the pathway for sperm de- posited in the vagina to reach the uterine tubes (see Figure 26.16). It is also the site of implantation of a fertilized ovum, develop- ment of the fetus during pregnancy, and labor. During reproduc- tive cycles when implantation does not occur, the uterus is the source of menstrual flow. Situated between the urinary bladder and the rectum, the uterus is the size and shape of an inverted pear (see Figure 26.11). In females who have never been pregnant, it is about 7.5 cm (3 in.) long, 5 cm (2 in.) wide, and 2.5 cm (1 in.) thick. The uterus is larger in females who have recently been pregnant, and smaller (atrophied) when sex hormone levels are low, as occurs after menopause.

The serosa is composed of

simple squamous epithelium (mesothelium), which is also called the visceral peritoneum, and an underlying areolar con- nective tissue. At the lesser curvature, the stomach's mesothelium bends back from the stomach and extends superiorly to connect to the liver as the lesser omentum. At the greater curvature, the stomach's mesothelium forms a large inferior fold, the greater omentum, which drapes over the intestines and doubles back on itself to attach to the transverse colon.

vasa vasorum

small vessels that supply blood to the tissues of the vessel

The epididymis also stores

sperm and during sexual arousal helps propel sperm into the ductus (vas) deferens by peristaltic contraction of its smooth muscle. Sperm may remain in storage in the epididymis for up to several months. Any stored sperm that are not ejaculated by that time are eventually phagocytized and reabsorbed.

The testes produce

sperm and secrete hormones

Semen contains

sperm plus the secretions provided by the accessory sex glands. The supporting structures have various functions. The penis de- livers sperm into the female reproductive tract and the scrotum supports the testes.

The walls of the seminiferous tubules contain two types of cells:

spermatogenic cells (sper -ma-toˉ-JEN-ik), the sperm-forming cells, and sustentacular cells (sus -ten-TAK-u ̄-lar) or Sertoli cells (ser-TO ̄ -leˉ ), which have several functions in supporting sperma- togenesis (Figure 26.4).

Spermatogonia are a type of

stem cells; when they undergo mitosis, some cells remain near the base- ment membrane of the seminiferous tubule in an undifferentiated state to serve as a reservoir of cells for future cell division and sub- sequent sperm production.

LH

stimulates the further development of follicles and their full secretion of estrogens. At midcycle, LH triggers ovulation and then promotes formation of the corpus luteum (the reason for the name luteinizing hormone). Stimulated by LH, the corpus luteum produces and secretes estrogens, pro- gesterone, relaxin, and inhibin.

The nerves to the small intestine are

supplied by the superior mesenteric plexus. The branches of the plexus contain postgangli- onic sympathetic fibers, preganglionic parasympathetic fibers, and sensory fibers. The sensory fibers are components of the vagus (X) nerves and spinal nerves via the sympathetic pathways. In the wall of the small intestine are two autonomic plexuses: the myenteric plexus between the muscular layers and the submucosal plexus in the submucosa. The nerve fibers to the smooth muscle of the blood vessels arise chiefly from the sympathetic division of the autonomic nervous system, while the nerve fibers to the smooth muscle of the intestinal wall originate from the vagus (X) nerves.

Sustentacular cells

support and protect developing sperma- togenic cells in several ways. They nourish spermatocytes, sper- matids, and sperm; phagocytize excess spermatid cytoplasm as development proceeds; and control movements of spermatogenic cells and the release of sperm into the lumen of the seminifer- ous tubule. They also produce fluid for sperm transport, secrete the hormone inhibin, which decreases the rate of spermatogen- esis, and regulate the effects of testosterone and FSH

Sustentacular cells

support and protect developing sperma- togenic cells in several ways. They nourish spermatocytes, sper- matids, and sperm; phagocytize excess spermatid cytoplasm as development proceeds; and control movements of spermatogenic cells and the release of sperm into the lumen of the seminifer- ous tubule. They also produce fluid for sperm transport, secrete the hormone inhibin, which decreases the rate of spermatogen- esis, and regulate the effects of testosterone and FSH (follicle- stimulating hormone).

cardia

surrounds the opening of the esophagus into the stomach.

The uterine tubes are supplied with

sympathetic and parasym- pathetic nerve fibers from the hypogastric plexus and the pelvic splanchnic nerves. The fibers are distributed to the muscular coat of the tubes and their blood vessels.

The salivary glands receive both

sympathetic and parasympa- thetic innervation. The sympathetic fibers form plexuses on the blood vessels that supply the glands and initiate vasoconstriction, which decreases the production of saliva. The parotid gland re- ceives sympathetic fibers from the plexus on the external carotid artery; the submandibular and sublingual glands receive sympa- thetic fibers that contribute to the sympathetic plexus and accom- pany the facial artery to the glands. The parasympathetic fibers of the glands produce vasodilation and stimulate the glandular cells of the glands, thus increasing the production of saliva.

blood reservoirs

systemic veins and venules contain a large percentage of the blood volume

spermatogenesis: full steps

takes about 65-75 days. It begins in the spermatogonia, which contain the diploid (2n) chromo- some number (Figure 26.5). Spermatogonia are a type of stem cells; when they undergo mitosis, some cells remain near the base- ment membrane of the seminiferous tubule in an undifferentiated state to serve as a reservoir of cells for future cell division and sub- sequent sperm production. The rest of the cells lose contact with the basement membrane, squeeze through the tight junctions of the blood-testis barrier, undergo developmental changes, and differentiate into primary spermatocytes (SPER-ma-toˉ -s ̄ı tz ). Primary spermatocytes, like spermatogonia, are diploid (2n); that is, they have 46 chromosomes. Shortly after it forms, each primary spermatocyte replicates its DNA, and then meiosis begins (Figure 26.5). In meiosis I, homologous pairs of chromosomes line up at the metaphase plate, and crossing-over occurs. Then the meiotic spindle pulls one (duplicated) chromosome of each pair to an opposite pole of the dividing cell. The two cells formed by meiosis I are called secondary spermatocytes. Each secondary spermato- cyte has 23 chromosomes, the haploid number (n). Each chro- mosome within a secondary spermatocyte, however, is made up of two chromatids (two copies of the DNA) still attached by a centromere. No replication of DNA occurs in the secondary spermatocytes. In meiosis II, no replication of DNA occurs. The chromo- somes line up in single file along the metaphase plate, and the two chromatids of each chromosome separate. The four haploid cells resulting from meiosis II are called spermatids (SPER- ma-tids). A single primary spermatocyte therefore produces four spermatids through two rounds of cell division (meiosis I and meiosis II). A unique process occurs during spermatogenesis. As the sperm cells proliferate following their production by spermatogonia, they fail to complete cytoplasmic separation (cytokinesis). The cells remain in contact by cytoplasmic bridges through their entire development (Figure 26.5). This pattern of development most likely accounts for the synchronized production of sperm in any given area of a seminiferous tubule. It may have survival value in that half of the sperm contain an X chromosome and half contain a Y chromosome. The larger X chromosome may carry genes needed for spermatogenesis that are lacking on the smaller Y chromosome. The final stage of spermatogenesis, spermiogenesis (sper - meˉ-oˉ-JEN-e-sis), is the maturation of haploid spermatids into sperm. Because no cell division occurs in spermiogenesis, each spermatid develops into a single sperm cell. During this process, spherical spermatids transform into elongated, slender sperm. An acrosome (described shortly) forms atop the condensing and elongating nucleus, a flagellum develops, and mitochondria mul- tiply. Sustentacular cells dispose of the excess cytoplasm that is sloughed off during this process. Finally, sperm are released from their connections toˉsustentacular cells, an event known as sper- miation (sper -meˉ-A-shun). Sperm then enter the lumen of the seminiferous tubule. Fluid secreted by sustentacular cells pushes sperm along their way, toward the ducts of the testes. At this point, sperm are not yet able to swim.

primor- dial germ cells

that arise from the yolk sac endoderm and enter the tes- tes during the fifth week of development. In the embryonic tes- tes, the primordial germ cells differentiate into spermatogonia, which remain dormant during childhood and become active at puberty. Toward the lumen of the tubule are layers of progres- sively more mature cells. In order of advancing maturity, these are primary spermatocytes, secondary spermatocytes, spermatids, and sperm cells.

fibromusculocartilaginous layer

the 16-20 incomplete horizontal rings of hyaline cartilage resemble the letter C. The rings are stacked one above another and are joined together by dense connective tissue. They may be felt through the skin infe- rior to the larynx. The open part of each C-shaped cartilage ring faces posteriorly toward the esophagus (Figure 23.5) and is spanned by a fibromuscular membrane. Within this membrane are transverse smooth muscle fibers, called the trachealis muscle (tra ̄-ke ̄-A-lis), and elastic connective tissue that allows the diam- eter of the trachea to change subtly during inhalation and exhala- tion, which is important in maintaining an efficient flow of air. The solid C-shaped cartilage rings provide a semi-rigid support to maintain patency so that the tracheal wall does not collapse inward (especially during inhalation) and obstruct the air passage- way.

The arterial supply of the pharynx includes

the ascending pha- ryngeal artery, the ascending palatine branch of the facial artery, the descending palatine and pharyngeal branches of the maxillary artery, and the muscular branches of the superior thyroid artery. The veins of the pharynx are similar in name to the arteries and drain into the pterygoid plexus and the internal jugular veins.

The stomach has four main regions:

the cardia, fundus, body, and pyloric part

macula densa

the columnar tubule cells in this region are crowded together

visceral pleura

the deep layer, the visceral pleura, adheres to the lungs

arteries of the esophagus, the esophageal arteries, arise from

the following arteries along its length: inferior thyroid, thoracic aorta, intercostal arteries, phrenic, and left gastric arteries. The es- ophagus is drained by the adjacent esophageal veins, which prima- rily drain into the various azygos veins. The esophagus is innervated by recurrent laryngeal branches of the vagus nerves, other branches of the vagus (X) nerves, and the cervical sympathetic chain.

Neighboring organs make indentations in the visceral surface of the spleen

the gastric impression (stomach), the renal impression (left kidney), and the colic impression (left colic flexure of the large intestine).

two components of a renal corpuscle are

the glomer- ulus (capillary network) and the glomerular capsule (Bowmen's capsule), a dead-end tube that surrounds the glomerular capillar- ies. The glomerular capsule is a double-walled cup with a cavity between the two layers that receives filtrate from the capillaries.

six major peritoneal folds:

the greater omentum, falciform ligament, lesser omentum, mesen- tery, transverse mesocolon, and sigmoid mesocolon.

The muscularis is composed of three layers;

the inner and outer layers are longitu- dinal, and the middle layer is circular

The penis has a very rich blood supply from the

the internal pu- dendal artery and the femoral artery. The capillaries drain via veins that parallel the arteries and have corresponding names.

The blood supply of the scrotum arises from

the internal pu- dendal branch of the internal iliac artery, the cremasteric branch of the inferior epigastric artery, and the external pudendal artery from the femoral artery. The scrotal veins follow the arteries.

hCG

the key hormone in the maintenance of pregnancy and the hormone that is detected by a home pregnancy test. Its presence in the maternal urine or blood is an indication that an implanted embryo is present in the uterus. Human chorionic gonadotropin mimics a maternal hormone, luteinizing hormone (LH), which maintains the endocrine secretions of progesterone and estrogens from the ovary. In the typical menstrual cycle, LH production declines, resulting in uterine contractions and the expulsion of the endometrium from the uterus. If this were to happen during pregnancy the embryo would be aborted. By pro- ducing hCG, the embryo ensures the continuation of pregnancy. Peak secretion of hCG occurs about the ninth week of pregnancy, at which time the placenta is well developed and can now produce the progesterone and estrogens on its own.

thyroid cartilage

the largest cartilage of the larynx, con- sists of two fused plates of hyaline cartilage that form the upper anterior and lateral walls of the larynx and give it a triangular shape. The anterior junction of the two plates forms the laryngeal prominence (Adam's apple). It is usually larger in males than in females due to the influence of male sex hormones on its growth during puberty. Above the prominence is a V-shaped notch that can be palpated with your fingertip. The ligament that connects the thyroid cartilage to the hyoid bone just superior to it is called the thyrohyoid membrane

The ovarian blood supply is furnished by

the ovarian arteries, which anastomose with branches of the uterine arteries. The ovaries are drained by the ovarian veins. On the right side they drain into the inferior vena cava, and on the left side they drain into the renal vein. Sympathetic and parasympathetic nerve fib- ers to the ovaries terminate on the blood vessels and enter the ovaries.

1. The organs of reproduction in females include

the ovaries, uterine (fallopian) tubes, uterus, vagina, vulva, and mammary glands.

The arterial supply of

the pancreas is from the superior and infe- rior pancreaticoduodenal arteries and from the splenic and superior mesenteric arteries. The veins, in general, correspond to the arter- ies. Venous blood reaches the hepatic portal vein by means of the splenic and superior mesenteric veins.

the uterus consists of three layers of tissue

the perimetrium, myometrium, and endometrium

Most of the muscles of the pharynx are innervated by nerve branches from

the pharyngeal plexus supplied by the glossopha- ryngeal (IX) and vagus (X) nerves.

Ejaculation

the pow- erful release of semen from the urethra to the exterior, is a sympa- thetic reflex coordinated by the lumbar portion of the spinal cord. As part of the reflex, the smooth muscle sphincter at the base of the urinary bladder closes. Therefore, urine is not expelled dur- ing ejaculation, and semen does not normally enter the urinary bladder. Even before ejaculation occurs, peristaltic contractions in the ampulla of the ductus deferens, seminal vesicles, ejacula- tory ducts, and prostate propel semen into the penile portion of the urethra (spongy urethra). Typically, this leads to emission (eˉ-MISH-un), the discharge of a small volume of semen before ejaculation. Emission may also occur during sleep (nocturnal emis- sion). The musculature of the penis (bulbospongiosus, ischiocav- ernosus, and superficial transverse perineal muscles), which is supplied by the pudendal nerve, also contracts at ejaculation

Type I alveolar cells

the predominant cells, are simple squamous epithelial cells that form a nearly continuous lining of the alveolar wall.

The first evidence of gastrulation is the formation of

the primi- tive streak, a faint groove on the dorsal surface of the epiblast that elongates from the posterior to the anterior part of the em- bryo (Figure 4.7a). The primitive streak clearly establishes the head and tail ends of the embryo, as well as its right and left sides. At the head end of the primitive streak a small group of epiblast cells forms a rounded structure called the primitive node.

The first kidney to form

the pronephros (proˉ -NEF-roˉ s; pro- before; nephros kidney), is the most superior of the three and has an associated pronephric duct. This duct empties into the cloaca (kloˉ -Aˉ -ka), the expanded terminal part of the hindgut, which functions as a common outlet for the urinary, digestive, and reproductive ducts. The pronephros begins to degenerate during the fourth week and is completely gone by the sixth week.

Three pairs of kidneys form within the intermediate mesoderm in succession:

the pronephros, the mesonephros, and the metanephros

The scrotal nerves arise from

the pudendal nerve, posterior cutaneous nerve of the thigh, and ilioinguinal nerves.

Ovulation

the rupture of the mature (graafian) follicle and the overlying germinal epithelium of the ovary and the release of the secondary oocyte into the peritoneal cavity, usually occurs on day 14 in a 28-day cycle. During ovulation, the secondary oocyte re- mains surrounded by its zona pellucida and corona radiata. Devel- opment of a secondary follicle into a fully mature follicle generally takes a total of about 20 days (spanning the last 6 days of the pre- vious cycle and the first 14 days of the current cycle). During this time the primary oocyte completes meiosis I to become a second- ary oocyte; the secondary oocyte then begins meiosis II but halts in metaphase until it is fertilized. From time to time, an oocyte is lost into the peritoneal cavity, where it later disintegrates. The small amount of blood that sometimes leaks into the peritoneal cavity from the ruptured follicle can cause pain, known as mit- telschmerz (MIT-el-shmarts pain in the middle), at the time of ovulation. An over-the-counter home test that detects a rising level of LH can be used to predict ovulation a day in advance.

external nose

the skin and muscle-covered portion of the nose visible on the face, is an extension of bone and cartilage with an internal dividing wall and two entryways (the nostrils). The na- sal bones project anteriorly to form the upper bony framework or "bridge" of the external nose on which a pair of glasses rest. The cartilaginous framework of the external nose is made up of several pieces of hyaline cartilage connected to each other and to the bones by tough fibrous connective tissue

The adventitia

the superficial layer of the vagina, consists of areolar connective tissue (Figure 26.20a). It anchors the vagina to adjacent organs such as the urethra and urinary bladder anteri- orly, and the rectum and anal canal posteriorly

The arteries of the larynx are

the superior and inferior laryn- geal arteries. The superior and inferior laryngeal veins accom- pany the arteries. The superior laryngeal vein empties into the superior thyroid vein, and the inferior laryngeal vein empties into the inferior thyroid vein.

scrotum

the supporting structure for the testes, consists of loose skin and an underlying subcutane- ous layer that hangs from the root (attached portion) of the penis

Chemicals in the food stimulate receptors in taste buds on the tongue, and impulses are conveyed from

the taste buds to two salivary nuclei in the brain stem (superior and inferior salivatory nuclei). Returning parasympathetic impulses in fibers from these nuclei pass through the facial (VII) nerve to the sublingual and submandibular glands and via the glossopha- ryngeal (IX) nerve to the parotid gland to stimulate the secretion of saliva. Saliva continues to be heavily secreted for some time after food is swallowed; this flow of saliva washes out the mouth and dilutes and buffers the remnants of irritating chemicals. The smell, sight, sound, or thought of food may also stimulate secre- tion of saliva, hence the description "mouth-watering."

mechanical digestion

the teeth cut and grind food before it is swallowed, and then smooth muscles of the stomach and small intestine churn the food to further assist the process. As a result, food mol- ecules become dissolved and thoroughly mixed with diges- tive enzymes.

accessory digestive organs

the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. Teeth aid in the physical breakdown of food, and the tongue assists in chewing and swallowing. The other accessory digestive organs never come into direct contact with food. They produce or store se- cretions that flow into the GI tract through ducts and aid in the chemical breakdown of food.

Lymph passes from lymph trunks into two main channels

the thoracic duct and the right lymphatic duct, and then drains into venous blood. The thoracic (left lymphatic) duct, the main duct for return of lymph to blood, is about 38-45 cm (15-18 in.) long. It begins as a dilation called the cisterna chyli (sis-TER- na KI ̄-le ̄; cisterna cavity or reservoir) anterior to the second lum- bar vertebra. The cisterna chyli receives lymph from the right and left lumbar trunks and from the intestinal trunk. In the neck, the thoracic duct also receives lymph from the left jugular, left subclavian, and left bronchomediastinal trunks. So the thoracic duct receives lymph from the left side of the head, neck, and chest, the left free upper limb, and the entire body inferior to the ribs. The thoracic duct in turn drains lymph into venous blood at the junction of the left internal jugular and left subclavian veins. The right lymphatic duct (Figure 15.3) is about 1.2 cm (0.5 in.) long and receives lymph from the right jugular, right subclavian, and right bronchomediastinal trunks. Thus, the right lymphatic duct receives lymph from the upper-right side of the body. From the right lymphatic duct, lymph drains into venous blood at the junction of the right internal jugular and right subclavian veins.

mastication

the tongue manipulates food, the teeth grind it, and the food is mixed with saliva. As a result, the food is reduced to a soft, flexible mass called a bolus (bolos lump) that is easily swallowed. When food is first swallowed, it passes from the mouth into the pharynx.

The uterine tubes are supplied by branches of

the uterine ar- teries (see Figure 26.19) and ovarian arteries (see Figure 14.6b). Venous return is via the uterine veins.

muscular arteries

their tunica media contains more smooth muscle and fewer elastic fib- ers than elastic arteries. The large amount of smooth muscle, approximately three-quarters of the total mass, makes the walls of muscular arteries relatively thick. Thus, muscular arteries are capable of greater vasoconstriction and vasodilation to adjust the rate of blood flow. Muscular arteries have a well-defined internal elastic lamina, but a thin external elastic lamina. These two elas- tic laminae form the inner and outer boundaries of the muscular tunica media

single primary spermatocyte

therefore produces four spermatids through two rounds of cell division (meiosis I and meiosis II).

Bile

toward a central vein, bile flows in the opposite direction. Also present in the hepatic sinusoids are a modified macro- phage, fixed phagocytes called stellate reticuloendothelial cells (STEL-a ̄t re-tik -u ̄-loˉ-en -doˉ-THE ̄ -leˉ-al), Kupffer cells (KUP-fer), or hepatic macrophages, which destroy worn-out white and red blood cells, bacteria, and other foreign matter in the venous blood draining from the gastrointestinal tract. Together, a bile duct, branch of the hepatic artery, and branch of the hepatic vein are referred to as a portal triad (tri three). canaliculi (kan-a-LIK-u ̄ -l ̄ı small canals). These are small ducts between hepatocytes that collect bile produced by the hepatocytes. From bile canaliculi, bile passes into bile ductules and then bile ducts. The bile ducts merge and even- tually form the larger right and left hepatic ducts, which unite and exit the liver as the common hepatic duct (see Figure 24.12a-b). The common hepatic duct joins the cystic duct (cystic bladder) from the gallbladder to form the com- mon bile duct. From here, bile enters the duodenum of the small intestine to participate in digestion. When the small intestine is empty, the sphincter around the common bile duct at the entrance to the duodenum closes, and bile backs up into the cystic duct to the gallbladder for storage.

The duct system

transports and stores sperm, assists in their maturation, and conveys them to the exterior.

Continuous ambulatory peritoneal dialysis (CAPD)

uses the peritoneal lining of the abdominal cavity as the dialysis membrane to filter the blood. The tip of a catheter is surgically placed in the patient's peritoneal cavity and connected to a sterile dialysis solu- tion. The dialysis solution flows into the peritoneal cavity from a plastic container by gravity. The solution remains in the cavity until metabolic waste products, excess electrolytes, and extracellular fluid diffuse into the dialysis solution. The solution is then drained from the cavity by gravity into a sterile bag that is discarded. The proce- dure is repeated several times each day into the urinary bladder; urine is then discharged from the body through the single urethra (see Figure 25.1).

The cervical canal opens into the

uterine cavity at the internal os (os mouthlike opening) and into the vagina at the external os.

endometrium

vascular, glandular lining

The blood supply to the bronchi is

via the left and right bron- chial arteries. The veins that drain the bronchi are the right bron- chial vein, which enters the azygos vein, and the left bronchial vein, which empties into the accessory hemiazygos vein or the left superior intercostal vein.

seminiferous tu- bules

where sperm are produced

Anterior cardiac veins

which drain the right ventricle and open directly into the right atrium

principal cells

which have receptors for both antidiuretic hormone (ADH) and aldosterone, two hormones that regulate their functions

large intestine

which is about 1.5 m (5 ft) long and 6.5 cm (2.5 in.) in diameter in living humans and cadavers, extends from the ileum to the anus (Figure 24.19). The ascending colon and de- scending colon are retroperitoneal, while the remaining parts of the colon and cecum are attached to the posterior abdominal wall by their mesocolon (mez -oˉ-KO ̄ -lon), a double layer of peritoneum connecting the parietal peritoneum to the visceral peritoneum that contains the vascular and nervous supply to the organs (see Fig- ure 24.3a). Structurally, the four principal regions of the large in- testine are the cecum, colon, rectum, and anal canal (Figure 24.19a). The opening from the ileum into the large intestine is guarded by a fold of mucous membrane called the ileocecal sphincter or valve (il -eˉ -oˉ -SE ̄ -kal), which allows materials from the small intestine to pass into the large intestine. Hanging inferior to the ileocecal valve is the cecum, a small pouch about 6 cm (2.4 in.) long. Attached to the cecum is a twisted, coiled tube, measuring about 8 cm (3 in.) in length, called the appendix or vermiform appendix (VER-mi- form worm-shaped; appendix appendage). The mesentery of the appendix, called the mesoappendix (mes -oˉ -a-PEN-diks), attaches the appendix to the inferior part of the mesentery of the ileum. The appendix has a high concentration of lymphatic nodules, which con- trol the bacteria entering the large intestine by immune responses.

spongy (penile) urethra

which is about 15-20 cm (6-8 in.) long. The spongy urethra ends at the external urethral orifice.

ductus deferens or vas deferens

which is about 45 cm (18 in.) long, ascends along the posterior border of the epididymis, through the spermatic cord to the point in the lower abdominal wall where it passes through the inguinal canal (see Figure 26.2) to enter the pelvic cavity; there it loops over the ureter and passes over the side and down the posterior surface of the urinary bladder

major salivary glands

which lie beyond the oral mucosa. Their secretions empty into ducts that lead to the oral cavity. The three pairs of major sali- vary glands are the parotid, submandibular, and sublingual glands (Figure 24.5a). The parotid glands (pa-ROT-id; par- near; ot- ear) are located inferior and anterior to the ears, between the skin and the masseter muscle. Each secretes saliva into the oral cavity via a parotid duct or Stensen's duct that pierces the bucci- nator muscle to open into the vestibule opposite the second max- illary (upper) molar tooth. The submandibular glands (sub - man-DIB-u ̄-lar), found in the floor of the oral cavity beneath the base of the tongue, are medial and partly inferior to the mandi- ble. Their ducts, the submandibular ducts (Wharton's ducts), run under the mucosa on either side of the midline of the floor of the mouth and enter the oral cavity proper lateral to the lingual frenulum. The sublingual glands (sub -LING-gwal) are supe- rior to the submandibular glands. Their ducts, the lesser sublin- gual ducts (Rivinus' ducts), open into the floor of the mouth in the oral cavity proper.

extrinsic muscles of the tongue

which originate outside the tongue (attach to bones in the area) and insert into connec- tive tissues in the tongue, include the hyoglossus, genioglossus, and styloglossus muscles (see Figure 11.7). The extrinsic muscles move the tongue from side to side and in and out to maneuver food for chewing, shape the food into a rounded mass, and force the food to the back of the mouth for swallowing. They also form the floor of the mouth, hold the tongue in position, and assist in speech

intercalated cells

which play a role in the homeostasis of blood pH.

peritubular capill- aries

which surround tubular parts of the nephron in the renal cortex

Penis, erectile tissues

¥ 3 cylindrical masses of vessels, connective tissue and smooth muscle ¥ 2 corposa cavernosa - dorsolateral ¥ 1 corpora spongiosum - mid ventral - with urethra • Arteries dilate - (ANS controlled) • Blood rushes in - erection • Veins compressed - blood trapped - erection maintained • When arteries constrict, veins drain blood - erection lost • Sildenafil... a $ 2,000,000,000 market!

The following are the components of the vulva:

¥ Anterior to the vaginal and urethral openings is the mons pu- bis (MONZ PU ̄ -bis; mons mountain), an elevation of adipose tissue covered by skin and coarse pubic hair that cushions the pubic symphysis. ¥ From the mons pubis, two longitudinal folds of skin, the labia majora (LAˉ -beˉ -a ma-JO ̄ -ra; labia lips; majora larger; singu- lar is labium majus), extend inferiorly and posteriorly. The labia majora are covered by pubic hair and contain an abundance of adipose tissue, sebaceous (oil) glands, and apocrine sudorifer- ous (sweat) glands. They are homologous to the scrotum. ¥ Medial to the labia majora are two smaller folds of skin called the labia minora (mı ̄-NO ̄ -ra; minora smaller; singular is labium minus). Unlike the labia majora, the labia minora are devoid of pubic hair and fat and have few sudoriferous glands, but they do contain many sebaceous glands. The labia minora are homologous to the spongy (penile) urethra. ¥ The clitoris (KLI-to-ris) is a small cylindrical mass of erectile tissue and nerves located at the anterior junction of the labia mi- nora. A layer of skin called the prepuce of the clitoris (PRE ̄ -pus) is formed at the point where the labia minora unite and covers • The bulb of the vestibule (see Figure 26.22) consists of two elongated masses of erectile tissue just deep to the labia on either side of the vaginal orifice. The bulb of the vesti- bule becomes engorged with blood during sexual arousal, narrowing the vaginal orifice and placing pressure on the penis during intercourse. The bulb of the vestibule is ho- mologous to the corpus spongiosum and bulb of the penis in males.

Functions of the Urinary System

¥ Elimination of the metabolic waste products and foreign substances ¥ Fluid and electrolyte balance ¥ Blood volume ¥ Blood pressure (renin) ¥ Erythropoiesis (erythropoietin)

Breasts

¥ Mammaryglands-modifiedsudorificglands ¥ Areola,nipple,15-25lobes(suspensory-Cooper'sligaments) ¥ Lobes,lobules,alveoli ¥ Lactiferous duct (mammary duct) > lactiferous sinus (ampulla) > just below areola Non lactating breasts: ducts outnumber alveoli

Menstrual Cycle

¥ Menstrual phase (3-4 days): no fertilization, no more corpus luteum, decrease in gonadal hormones,contraction/relaxation of spiral arteries ¥ Proliferative, follicular or estrogenic phase (10 days) • Secretory, luteal or progesterogenic phase (14 days)

Epididymis

¥ Postero-lateral part of testis ¥ Comma shaped, temporary storage of sperm ¥ Sperm mature here - immobile to motile (~ 20 days) ¥ Stored for months, later phagocytosed ¥ Sperm ejaculated from here into vas deferens

function of gallbladder

¥ Processing of drugs and hormones. The liver can detoxify substances such as alcohol or secrete drugs such as penicil- lin, erythromycin, and sulfonamides into bile. It can also in- activate hormones such as thyroid hormones, estrogens, and aldosterone. ¥ Excretion of bilirubin. Bilirubin, derived from the heme of aged red blood cells, is absorbed by the liver from the blood and secreted into bile. Most of the bilirubin in bile is metabo- lized in the small intestine by bacteria and eliminated in feces. ¥ Synthesisofbilesalts.Bilesaltsareusedinthesmallintestine for the emulsification and absorption of lipids, cholesterol, phospholipids, and lipoproteins. ¥ Storage. In addition to glycogen, the liver is a prime storage site for certain vitamins (A, B12, D, E, and K) and minerals (iron and copper), which are released from the liver when needed elsewhere in the body. ¥ Phagocytosis. The stellate reticuloendothelial (Kupffer) cells of the liver phagocytize aged red blood cells and white blood cells and some bacteria. ¥ ActivationofvitaminD.Theskin,liver,andkidneyspartici- pate in synthesizing the active form of vitamin D.

seminal vesicle and prostate

¥ Seminal vescicle (tubular gland;70%) & prostrate (tubuloalveolar gland; 30%) - secrete components of semen

ovarian medulla

¥ is deep to the ovarian cortex. The bor- der between the cortex and medulla is indistinct, but the me- dulla consists of more loosely arranged connective tissue and contains blood vessels, lymphatic vessels, and nerves.

Cortical nephron

• • Has short loop of Henle and glomerulus further from the corticomedullary junction • Efferent arteriole supplies peritubular

In addition to secreting bile, the liver performs many other vital functions:

• Carbohydrate metabolism. The liver is especially important in maintaining a normal blood glucose level. When blood glu- cose is low, the liver can break down glycogen to glucose and release glucose into the bloodstream. The liver can also con- vert certain amino acids and lactic acid to glucose, and it can convert other sugars, such as fructose and galactose, into glu- cose. When blood glucose is high, as occurs just after eating a meal, the liver converts glucose to glycogen and triglycerides for storage. • Lipid metabolism. Hepatocytes store some triglycerides; break down fatty acids to generate ATP; synthesize lipopro- teins (HDLs, LDLs, VLDLs), which transport fatty acids, triglycerides, and cholesterol to and from body cells; synthe- size cholesterol; and use cholesterol to make bile salts. • Protein metabolism. Hepatocytes deaminate [remove the amino group (2NH2) from] amino acids so that the amino acids can be

Menopause

• Cessation of uterine cycles • Ovaries unresponsive to gonadotropic hormones • No secretion of estrogen and progesterone • Cycles - irregular before stopping • Physical symptoms manifested

Accessory organs

• Fallopian tubes, uterine tubes - ovaries to uterus • No direct connection • oocytes > FT > uterus • FT - fertilization site - not implantation

Juxtamedullary nephron

• Has long loop of Henle and glomerulus closer to the corticomedullary junction • Efferent arteriole supplies vasa recta Cortical radiate vein Cortical radiate artery

Female reproductive system

• Internal genitalia ovaries, duct system (uterus, oviducts - Fallopian, vagina) • External genitalia vulva (mons pubis, clitoris, labia minora, vestibule, greater vestibular glands - Bartholin's) • ovaries - primary, paired, almond sized • held by ligaments, mainly broad and ovarian • hormones - estrogen, progesterone • saclike follicles - oocytes with cell layers around • ovulation; corpus luteum

Functions of the kidneys include the following:

• Regulation of blood ionic composition. The kidneys help regu- late the blood levels of several ions, most importantly sodium Urine formed by the kidneys passes first into the ureters, then to the urinary bladder for storage, and finally through the urethra for elimination from the body. ¥ Regulation of blood pH. The kidneys excrete a variable amount of hydrogen ions (H ) into the urine and conserve bicarbonate ions (HCO3 ). Both of these activities help reg- ulate blood pH. ¥ Regulation of blood volume. The kidneys adjust blood volume by conserving or eliminating water in the urine. An increase in blood volume increases blood pressure; a decrease in blood volume decreases blood pressure. ¥ Enzymatic regulation of blood pressure. The kidneys also help regulate blood pressure by secreting the enzyme renin, which indirectly causes an increase in blood pressure. Maintenance of blood osmolarity. By separately regulating loss of water and loss of solutes in the urine, the kidneys main- tain a relatively constant blood osmolarity. The osmolarity of a solution is a measure of the total number of dissolved parti¥ - cles per liter of solution. ¥ Production of hormones. The kidneys produce two hormones. Calcitriol, the active form of vitamin D, helps regulate calcium homeostasis, and erythropoietin stimulates the production of red blood cells. • Regulation of blood glucose level. Like the liver, the kidneys can use the amino acid glutamine in gluconeogenesis, the syn- thesis of new glucose molecules. They can then release glucose into the blood to help maintain a normal blood glucose level. • Excretion of wastes and foreign substances. By forming urine, the kidneys help excrete wastes—substances that have no use- ful function in the body. Some wastes excreted in urine result from metabolic reactions in the body. These include ammonia and urea from the deamination of amino acids; bilirubin from the catabolism of hemoglobin; creatinine from the breakdown of creatine phosphate in muscle fibers; and uric acid from the catabolism of nucleic acids. Other wastes excreted in urine are foreign substances from the diet, such as drugs and environ- mental toxins.

Male reproductive system Major structures

• Testes • Epididymis • Vas deferens • Seminal vesicle • Prostrate • Urethra • Penis

What is a portal system?

• Usually: arterioles > capillaries > venules > systemic return • In a portal system: arterioles > capillaries > vein > capillaries > venules > systemic return

Uterus

• pear shaped, houses developing embryo • Fundus, body, cervix • Endometrium, Myometrium, Serosa or adventitia • Endometrium (functional, basal) • Fertilized egg burrows into endometrium (implantation) • If not pregnant, endometrium shed every 28 days

External genitalia

• vulva - perineal region - L. majora, L. minora ¥ clitoris - counterpart of penis (no urethra) ¥ vestibule - anterior urethral orifice, posterior vaginal orifice ¥ Bartholin's glands - mucous lubricant

Whole blood is composed of two portions:

(1) blood plasma, a watery liquid extracellular matrix that contains dissolved sub- stances, and (2) formed elements, which are cells and cell frag- ments. Blood is about 45 percent formed elements and 55 percent blood plasma. Normally, more than 99 percent of the formed elements are red-colored cells called red blood cells (RBCs). Pale or colorless white blood cells (WBCs) and plate- lets make up less than 1 percent of the formed elements. They form a very thin layer, called the buffy coat, between the packed RBCs and blood plasma in centrifuged blood. shows the composition of blood plasma and the numbers of the various types of formed elements in blood.

On the twenty-second day, the primitive heart tube develops into five distinct regions and begins to pump blood. From tail end to head end (also the direction of blood flow) they are the

(1) sinus venosus, (2) primitive atrium, (3) primitive ventricle, (4) bulbus cordis, and (5) truncus arteriosus

blood has three general functions

1. Transportation. 2. Regulation 3. Protection

Blood Plasma

When the formed elements are removed from blood, a straw- colored liquid called blood plasma (or simply plasma) is left. Plasma is about 91.5 percent water and 8.5 percent solutes, most of which (7 percent by weight) are proteins. Some of the proteins in plasma are also found elsewhere in the body, but those confined to blood are called plasma proteins. Hepato- cytes (liver cells) synthesize most of the plasma proteins, which include the albumins (54 percent of plasma pro- teins), globulins (38 percent), and fibrinogens (7 percent). Some blood cells develop into plasma cells that produce globulins called immunoglobulins, also called antibodies because they are formed elements (red blood cells, white blood cells, and platelets).

anemia

a condition in which the blood has a reduced oxygen-carrying capacity

. A hemoglobin molecule consists of

a protein called globin, composed of four polypeptide chains (two alpha and two beta chains), plus four nonprotein pigments called hemes

Lipoprotein (a

an LDL-like particle that attaches to endothelial cells, macrophages, and blood platelets, inhibits blood clot breakdown and may promote smooth muscle fiber proliferation.

mediastinum

an anatomical region that extends from the sternum to the vertebral column, the first rib to the diaphragm, and between the coverings (pleurae) of the lungs

Great cardiac vein

in the anterior interventricular sulcus, which drains the areas of the heart supplied by the left coro- nary artery (left and right ventricles and left atrium)

Granular leukocytes include

neutrophils, eosinophils, and basophils

fibrillation

refers to rapid, uncoordinated heartbeats.

foramen ovale

the interatrial septum and endocardial cushions unite and an opening in the septum

Spontaneous Rhythmic Contractions

• Specialized cardiac muscle cells form cardiac conducting system (SA and AV nodes and Purkinje fibers - modified cardiomyocytes). • Parasympathetic and sympathetic nerve endings located in the nodes. (What is the function of this innervation?)

conduction system

➊ Normally, cardiac excitation begins in the sinoatrial (SA) node, located in the right atrial wall just inferior and lat- eral to the opening of the superior vena cava. Each action potential from the SA node conducts through conduction cells to the contractile cardiac muscle cells of both atria via gap junctions in the intercalated discs of these fibers. With the arrival of the action potential, the two atria contract at the same time. ➋ By conducting along modified atrial muscle fibers called inter- nodal fibers, the action potential reaches the atrioventricular (AV) node, located in the interatrial septum, just anterior to the opening of the coronary sinus. At the AV node, the action potential slows considerably as a result of various differences in cell structure in the AV node. This delay provides time for the atria to empty their blood into the ventricles. ➌ From the AV node, the action potential enters the atrio- ventricular (AV) bundle (also known as the bundle of His, pronounced hiz), the only site where action potentials can conduct from the atria to the ventricles. (Elsewhere, the fibrous skeleton of the heart electrically insulates the atria from the ventricles.) ➍ After conducting through the AV bundle, the action poten- tial then enters both the right and left bundle branches, which course through the interventricular septum toward the apex of the heart. ➎ Finally, the large-diameter Purkinje fibers (pur-KIN-jeˉ) leave their insulating connective tissue sheaths near the apex of the heart and relay the action potential to the contractile cells of the ventricular myocardium. As the wave of ventricu- lar contraction moves upward from the apex, the blood is pushed toward the semilunar valves. The ventricular con- traction occurs about 0.20 sec (20 milliseconds) after atrial contraction.

The pericardium consists of two principal portions:

(1) the fibrous pericardium and (2) the serous pericardium

Lymph Node

1 capsule 2 nodule 3 subcapsular sinus 4 trabecular sinus 5 medullary cords 6 medullary sinus 7 trabecula

blood function

1. Transports oxygen, carbon dioxide, nutrients, hormones, heat, and wastes. 2. Regulates pH, body temperature, and water content of cells. 3. Protects against blood loss through clotting, and against disease through phagocytic white blood cells and proteins such as antibodies, interferons, and complement.

electrocardiogram

An EKG is a composite of all the action potentials generated by nodal and contractile cells. Three clearly recognizable up-and-down waves normally ac- company each cardiac cycle The first, called the P wave, is the spread of depolarization from the SA node through the two atria. A fraction of a second after the P wave begins, an action potential occurs and the atria contract. The second wave, called the QRS wave, is the spread of the depolarization through the ventricles. Shortly after the QRS wave begins, an action po- tential is reached and the ventricles contract. The third wave, the T wave, indicates ventricular repolarization, which corresponds to the relocation of ventricular muscle fibers. There is no wave to show atrial repolarization because the stronger QRS wave masks this event.

Protection

Blood can clot (become gel-like), which protects against its excessive loss from the cardiovascular system after an injury. In addition, white blood cells protect against disease by carrying on phagocytosis. Several types of blood proteins, including antibodies, interferons, and complement, help pro- tect against disease in a variety of ways

Transportation

Blood transports oxygen from the lungs to the cells of the body and carries carbon dioxide from the body cells to the lungs for exhalation. It carries nutrients from the gastrointestinal tract to body cells and hormones from endocrine glands to cells throughout the body. Blood also transports heat and waste products to the lungs, kid- neys, and skin for elimination from the body.

cardiac plexus

Cardiac branches of the parasym- pathetic vagus (X) nerve and cardiac branches from the cervical and upper thoracic sympathetic trunk unite around the heart to form

Regulation

Circulatingbloodhelpsmaintainhomeostasisinall body fluids. Blood plays a role in the regulation of pH through buffers. (Buffers are chemicals that convert strong acids or bases into weak ones.) It also assists in the adjustment of body tem- perature; the heat-absorbing and coolant properties of the water in blood plasma and its variable rate of flow through the skin allow excess heat to be lost from the blood to the environment. Blood osmotic pressure also influences the water content of cells, mainly through interactions of dissolved ions and proteins.

White blood cells (leukocytes)

I. A. Granular leukocytes (contain conspicuous granules that are visible under light microscope after staining) 1. Neutrophils 2. Eosinophils 3. Basophils B. Agranular leukocytes (no granules are visible under a light microscope after staining) 1. T and B lymphocytes and natural killer (NK) cells 2. Monocytes

fibrous pericardium

I. is composed of tough, inelastic, dense irregular connective tissue. It resembles a bag that rests on and attaches to the diaphragm; the open end of the bag is fused to the connective tissues of the blood vessels entering and leaving the heart.

General Structure of the GI Tract

• Mucosa(epithelium+laminapropria+lamina muscularis mucosae) • Submucosa(connectivetissuewithblood/lymph vessels, glands and nerve plexus) • Muscularisexterna(smoothmuscleandnerve plexus) • Serosa("3Ps")orAdventitia(connectivetissuewith blood/lymph vessels, nerves) (pink, pulse, peristalsis)

Primitive ventricle

Left ventricle

Sinus venosus

Part of right atrium (posterior wall), coronary sinus

myocardial ischemia

Partial obstruction of blood flow in the coronary ar- teries

Liver

• Processing and storage of nutrients from the GI tract via portal vein (complex lipids arrive via lymph vessels) • Neutralizing and eliminating toxins and drugs • Iron metabolism • Synthesis of plasma proteins, coagulation and growth factors

Polycythemia

is an increase in the percentage of RBCs in which the hematocrit is above 54 percent

Organs Associated with the GI Tract

• Salivary glands • Liver Bile, Common hepatic duct • Gall bladder Bile storage, CHD to duodenum • Pancreas Triangular gland, hormones and enzymes to SI

Pancreas

• Exocrine: proteases (trypsinogens, chymotrypsinogens, etc.), amylases, lipases, phospholipases, nucleases (deoxy- and ribo- nuclease). • Endocrine (Islets of Langerhans): cell type A (glucagon), B (insulin), D (somatostatin) and F (pancreatic polypeptide).

trabeculae carneae

The inside of the right ventricle contains a series of ridges formed by raised bundles of cardiac muscle fibers

Eosinophil

The large, uniform-sized granules within an eosinophil are eosinophilic ( eosin-loving)—they stain red-orange with acidic dyes The granules usually do not cover or obscure the nucleus, which most often has two or three lobes connected by either a thin strand or a thick strand of nuclear material.

The Cardiovascular System

• Heart • Blood vessels (arteries, veins, capillaries) • Blood • Lymphatic vessels (capillaries, larger vessels)

What's that lub-dub?

• Lub - closure of bicuspid and tricuspid valves • Dub - closure of semilunar valves

Monocyte

The nucleus of a monocyte is usually kidney-shaped or horseshoe-shaped, and the cyto- plasm is blue-gray and has a foamy appearance (Figure 12.5e). The cytoplasm's color and appearance are due to very fine azurophilic granules (az -u ̄-roˉ-FIL-ik; azur blue; philos loving), which are lysosomes. Blood is merely a con- duit for monocytes, which migrate from the blood into the tissues, where they enlarge and differentiate into macro- phages (MAK-roˉ-fa ̄-jez large eaters). Some become fixed (tissue) macrophages, which means they reside in a partic- ular tissue; examples are alveolar macrophages in the lungs or macrophages in the spleen. Others become wandering macrophages, which roam the tissues and gather at sites of infection or inflammation.

Saliva

• Lubrication • Digestion of carbohydrates and lipids (amylase, lipase) • Germicidal protection (IgA, lysozyme, lactoferrin) • Teeth protection (Ca-binding proline-rich salivary proteins)

Basophil

The round, variable-sized granules of a basophil are basophilic ( basic loving)—they stain blue-purple with basic dyes The granules commonly ob- scure the nucleus, which has two lobes.

pericardial cavity

The space that contains the few milliliters of pericardial fluid

Lymphoid Organs

• Lymphoid nodules, diffuse lymphocytes in tonsils • Peyer's patches of the ileum • Vermiform appendix • Thymus • Lymph nodes • Spleen • Red bone marrow

Fibrinogen

a glycoprotein involved in blood clotting, may help regulate cellular proliferation, vasocon- striction, and platelet aggregation.

C- reactive proteins (CRPs)

are proteins produced by the liver or present in blood in an inactive form that are converted to an active form during inflammation. CRPs may play a direct role in the development of athero- sclerosis by promoting the uptake of LDL by macrophages.

Chronic pericarditis

begins gradually and is long-lasting. In one form of this condition, there is a buildup of pericardial fluid. If a great deal of fluid accumulates, this is a life-threatening condition because the fluid compresses the heart, a condition called cardiac tamponade (tam -pon-AˉD). As a result of the compression, ventricular filling is decreased, cardiac output is reduced, venous return to the heart is di- minished, blood pressure falls, and breathing is difficult. Most causes of chronic pericarditis involving cardiac tamponade are unknown, but it is sometimes caused by conditions such as cancer and tuberculo- sis. Treatment consists of draining the excess fluid through a needle passed into the pericardial cavity.

autorhythmic cells

cells that repeatedly and rhythmically generate action potentials. a natural pacemaker, setting the rhythm for the contraction of the entire heart, and they form the cardiac conduction system, the route that delivers action potentials throughout the heart muscle.

Blood

closely related to other body fluids. In fact, many of the extracellular body fluids (including interstitial fluid, lymph, cere- brospinal fluid, and aqueous humor) arise from the blood during development and are continually replenished by it. The extra- cellular fluids that nourish, protect, and exchange materials with every cell of the body are derived from the blood, renewed by the blood, and returned to the blood.

erythrocytes

contain the oxygen-carrying pro- tein hemoglobin (Hb), which is a pigment that gives whole blood its red color. biconcave discs

Systole

contraction

Characteristics of Blood

denser and more viscous (thicker) than water, which is part of the reason it flows more slowly than water. The tempera- ture of blood is about 38 C (100.4 F), which is slightly higher than normal body temperature, and it has a slightly alkaline pH ranging from 7.35 to 7.45. The color of blood varies. When satu- rated with oxygen it is bright red; when unsaturated with oxygen, the blood is dark red to purple. Blood constitutes about 8 percent of the total body weight. The blood volume is 5-6 liters (1.5 gal) in an average-sized adult male and 4-5 liters (1.2 gal) in an aver- age-sized adult female. This gender difference in volume is due to the difference in average body size.

deep coronary sulcus

encircles most of the heart and marks the external boundary between the superior atria and inferior ventricles

acute pericarditis

in most cases it has no known cause, but it is some- times linked to a viral infection. As a result of irritation to the peri- cardium, there is chest pain that may extend to the left shoulder and down the left arm (often mistaken for a heart attack), and pericardial friction rub (a scratchy or creaking sound heard through a stetho- scope as the visceral layer of the serous pericardium rubs against the parietal layer of the serous pericardium). Acute pericarditis usually lasts for about one week and is treated with drugs that reduce in- flammation and pain, such as ibuprofen or aspirin.

Small cardiac vein

in the coronary sulcus, which drains the right atrium and right ventricle

Middle cardiac vein

in the posterior interventricular sulcus, which drains the areas supplied by the posterior interven-tricular branch of the right coronary artery (left and right ventricles)

Red bone marrow

is a highly vascularized connective tissue located in the microscopic spaces between trabeculae of spongy bone tissue.

Thrombopoietin(TPO)

is a hormone produced by the liver that stimulates the formation of platelets (thrombocytes) from megakaryocytes.

pericardial fluid

is a slippery secretion of the pericardial cells that reduces friction between the membranes as the heart moves.

endocardium

is a thin layer of endothelium overlying a thin layer of connective tissue. It provides a smooth lining for the chambers of the heart and covers the valves of the heart. The smooth endothe- lial lining minimizes the surface friction as blood passes through the heart. The endocardium is continuous with the endothelial lining of the large blood vessels attached to the heart.

serous pericardium

is a thinner, more delicate membrane that forms a double layer around the heart The outer parietal layer of the serous pericardium is fused to the fibrous pericardium. The inner visceral layer of the serous pericardium, also called the epicardium when combined with the underlying areolar or adipose tissue, adheres tightly to the surface of the heart. Between the parietal and visceral layers of the serous pericardium is a thin film of lubricating fluid.

Homocysteine

is an amino acid that may induce blood vessel damage by promoting platelet aggregation and smooth muscle fiber proliferation.

epicardium

is composed of two tissue layers. The outermost, as you just learned, is also called the visceral layer of the serous pericardium. This thin, transparent outer layer of the heart wall is composed of mesothelium. Beneath the mesothelium is a variable layer of delicate fibroelastic tissue and adipose tissue. The adipose tissue predominates and becomes thickest over the ventricular surfaces, where it houses the major coronary and car- diac vessels of the heart. The amount of fat varies from person to person, corresponds to the general extent of body fat in an indi- vidual, and typically increases with age. The epicardium imparts a smooth, slippery texture to the outermost surface of the heart. The epicardium contains blood vessels, lymphatics, and nerves that supply the myocardium.

Coronary artery disease (CAD)

is defined as the effects of the accumulation of atherosclerotic plaques (described shortly) in coronary arteries that lead to a reduction in blood flow to the myocardium.

myocardium

is responsible for the pumping action of the heart and is composed of cardiac muscle tissue.

agranular leukocytes in- clude

lymphocytes and monocytes.

lipoproteins

molecules produced by the liver and small in- testine These spherical particles consist of an in- ner core of triglycerides and other lipids and an outer shell of proteins, phospholipids, and cholesterol. Most lipids, including cholesterol, do not dissolve in water; they must be made water-soluble in order to be transported in the blood. This is accomplished by combining the lipids with lipoproteins. Two major classes of lipoproteins are low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs). LDLs transport cholesterol from the liver to body cells for use in cell mem- brane repair and the production of steroid hormones and bile salts, but excessive amounts promote atherosclerosis, so the cholesterol in these particles is sometimes referred to as "bad cholesterol." HDLs remove excess cholesterol from body cells and transport it to the liver for elimi- nation. Because HDLs decrease blood cholesterol level, the cholesterol in HDLs is referred to as "good cholesterol." When you get your blood test results, you want your LDL to be low and your HDL to be high.

myeloid stem cells and lymphoid stem cells

produce two further types of stem cells, which have the capacity to develop into several kinds of cells

nitric oxide (NO),

produced by the endothelial cells that line blood vessels, binds to hemoglobin. Under some circumstances, hemoglobin releases NO. The released NO causes vasodilation, an increase in blood vessel diameter that occurs when the smooth muscle in the vessel wall relaxes. Vasodilation improves blood flow and en- hances oxygen delivery to cells near the site of NO release.

anastomoses

provide alternate routes called collat- eral circulation for blood to reach a particular organ or tissue.The myocardium contains many anastomoses that connect dif- ferent branches of the same coronary artery or extend between branches of different coronary arteries. They provide detours for arterial blood if a main route becomes obstructed. Thus, the heart muscle may receive sufficient oxygen even if one of its coro- nary arteries is partially blocked.

The formed elements of the blood include

red blood cells (RBCs), white blood cells (WBCs), and platelets

leukemia

refers to a group of red bone marrow cancers in which abnormal white blood cells multiply uncontrollably. Lymphoblastic leukemia (lim-foˉ -BLAS-tik) involves cells derived from lymphoid stem cells (lymphoblasts) and/ or lymphocytes. Myelogenous leukemia (mı ̄ -e-LOJ-e-nus) involves cells derived from myeloid stem cells (myeloblasts). Combining onset of symptoms and cells involved, there are four types of leukemia. 1. Acute lymphoblastic leukemia (ALL) is the most common leukemia in children, but adults can also get it. 2. Acute myelogenous leukemia (AML) affects both children and adults. 3. Chronic lymphoblastic anemia (CLA) is the most common leukemia in adults, usually those older than 55. Chronic myelogenous leukemia (CML) occurs mostly in adults. The cause of most types of leukemia is unknown. However, certain

Erythropoiesis

the production of RBCs, starts in the red bone marrow with a precursor cell called a proerythroblast The proerythroblast divides several times, producing cells that begin to synthesize hemoglobin. Ultimately, a cell near the end of the developmental sequence ejects its nucleus and becomes a reticulocyte. Loss of the nucleus causes the center of the cell to indent, producing the distinctive biconcave shape. Reticulocytes usu- ally develop into erythrocytes, or mature red blood cells, within 1-2 days after their release from red bone marrow.

Angina pectoris

which literally means "strangled chest," is a severe pain that usually accompanies myocardial ischemia.

Lymphatic nodules

¥ Caecum - at junction of ileum and large intestine ¥ Appendix - hangs from apex of caecum • Colon:ascending,transverse,ascendingandsigmoid • Sigmoid colon > rectum > narrows > anal canal > anus

Cardiac Muscle

¥ Linear cell-to-cell attachment (intercalated discs) of cardiac muscle cells (cardiomyocytes) - cardiac muscle fibers ¥ Centrally located nuclei ¥ Endomysium ¥ Cross striations (as in skeletal muscle)

The heart beat

¥ Sinoatrial node - SA node ¥ Wall of right atrium - near superior vena cava ¥ Modified cardiac cells - generate electrical impulse - pacemaker ¥ Pass down from atrium to ventricles - pushing blood down ¥ Fibrous tissue stops impulse (electrical signal) ¥ Atrioventricular node picks up - Purkinje fibres continue - conducted to ventricles