27,28,29

how long sperm can last after ejaculation

3 days

Ovulation

About day 14, a surge of hormones causes the ovum to burst through the ovary, . It usually occurs in the middle of the 28-day menstrual cycle (about 14 days before the onset of the next menses). Some fertility control and fertility enhancement methods are based on calculation of the time of . Some women experience sharp pains or cramps when ovulation occurs. This is known as mittelschmerz (meaning "middle pain" in German).

Progesterone

After puberty, the corpus luteum of the ovary produces another hormone, , which functions primarily during pregnancy. The pubescent girl exhibits many changes as a result of estrogen production. Characteristic secondary sexual characteristics of the female include a smaller stature, higher percentage of body fat, pubic and axillary hair, and development of breasts. The female pubic arch (subpubic angle) of the pelvis and hip structure is wider than that of the male, to facilitate childbirth. Sweat glands become more active. Although voice changes are not as marked as those in a boy, the voice does deepen and mature in tone and quality. As glands of reproduction become active, menstruation occurs. All female secondary sex characteristics depend on secretion of estrogens and progesterone.

ADH

Antidiuretic Hormone. In response to angiotensin II and low fluid levels, the posterior pituitary secretes ADH. ADH increases reabsorption of water by kidney tubules, thereby decreasing the amount and increasing the concentration of urine. The result is maintenance of circulating blood volume and blood pressure and, therefore, homeostasis.

androgen

As hormones from the hypothalamus, pituitary, and gonads are secreted during puberty(pubescence), the male is able to reproduce (see Chapter 11). In boys, puberty usually occurs between 12 and 16 years of age; full adult maturity is reached about age 20. Before puberty (prepubescence), blood concentrations of androgens (male hormones) and estrogens (female hormones) are the same in every person are a group of hormones that play a role in male traits and reproductive activity. Present in both males and females, the principle are testosterone and androstenedione. may be called "male hormones," but don't let the name fool you.

male sperm

Beginning at about 12 to 13 years of age and continuing throughout life, the seminiferous tubules of the testes (male gonads), stimulated by testosterone, form sperm cells. The sperm cell (plural is also sperm) is the male gamete, one of two cells (containing 23 chromosomes) that must unite to initiate development of a new individual. This formation of mature, functional spermatozoa is called spermatogenesis. Normal spermatogenesis does not occur if the testes are too warm or too cold (above or below 35°C [95°F]), as described above. Sperm cells develop from stem cells, spermatogonia (singular: spermatogonium). A "mother cell" helps create spermatogonia and a specific cell, the Sertoli cell, facilitates spermatogenesis. Spermatogonia divide by mitosis and then meiosis to form spermatocytes (see Chapter 15). In the next stage, the cells are spermatids, which eventually develop into spermatozoa (singular: spermatazoon), a total process requiring about two months. (Each primary spermatocyte forms four functional gametes.) The testes produce millions of spermatozoa each day and they are stored in the ductus deferens. Sperm cells are highly specialized and are have several divisions (Fig. 28-4). The head contains 23 chromosomes (half of the human genetic material) and the tip of the head, the acrosome, contains enzymes that can dissolve the tough cell wall of the ovum (female sex cell). The body (center sections) contains mitochondria, providing energy for locomotion. The whip-like tail is a flagellum that propels the sperm with a lashing motion. After sperm and semen combine in the ejaculatory duct, the ejaculatory fluid contains about 60 to 100 million sperm cells per milliliter. (Semen with a sperm count of less than 10 to 20 million per milliliter may have difficulty fertilizing an ovum.) The amount of semen ejaculated (expelled) varies from 2 to 5 mL. After ejaculation into a woman's vagina, a sperm cell can survive up to 3 days. Of the average 250 million sperm cells ejaculated, only about 100 survive to contact the ovum in the oviduct, although usually only one sperm fertilizes the ovum.

GFR

Glomerular filtrate contains water, glucose, urea, creatinine, and numerous electrolytes. The amount of filtrate formed in all glomeruli of both kidneys per minute is called the glomerular filtration rate (GFR). Normal GFR in an adult is about 125 mL/min (about 180 L/day). Glomerular filtration depends on relative pressures. The diameter of the afferent (entering) arteriole is greater than that of the efferent (leaving) arteriole, making it easier for blood to enter the glomerulus than to leave it. (Remember that glomerular blood pressure is much higher than that of other body capillaries

how urine production influenced

Normally, about 750 to 2,000 mL of urine is formed daily. Urine is formed in the nephron by glomerular filtration, tubular reabsorption, and tubular secretion. A fourth process allows additional water reabsorption via hormonal control (ADH). (This is often considered to be an integral part of the regulatory processes in urine formation.) These four steps are closely interrelated. Figure 27-7 illustrates the process of urine formation.

graphic follicle what does it become when released

Once it releases its egg, the empty ovarian follicle develops into a new structure called the corpus luteum. The corpus luteum secretes the hormones estrogen and progesterone he follicle is characterized by a large follicularantrum that makes up most of the follicle. ... When released from the Graafian follicle and into the oviduct, the ovum will consist of three structures: oocyte, zona pellucida and corona radiata.

vagina/ acidic

The cervix projects into a fibromuscular canal, about 4 in (10 cm) long, the (see Fig. 29-1). The vagina is attached to the uterus through the cervix and meets the external organs at the vulva. The vagina's superior, domed portion has deep recesses, fornices (singular: fornix), around the portion of the cervix extending into the vagina. Glandular secretions from Bartholin's glands (greater vestibular glands) and the mucous membrane lining its walls moisten the vagina. The mucus is acidic and retards microbial growth. (The alkaline semen can temporarily neutralize the vagina's acidic environment.) Rugae, expandable folds within the vaginal walls, accommodate insertion of the penis and passage of the fetus during childbirth. The vagina's functions are to receive sperm, provide an exit for menstrual flow, and serve as the birth canal. The hymen is a thin membrane over the vaginal opening. It may close the vaginal orifice completely, or it may be absent from birth. More commonly, it has one or more perforations. A woman can injure the hymen in various ways (e.g., during normal exercise, horseback riding, by using tampons, or during the first sexual intercourse). The presence or absence of a hymen is not a reliable indicator of a woman's virginity. needs to have certain types of the bacteria lactobacillus, which produce high levels of lactic acid. The study found this lactobacillus make the vagina acidic, which is important in helping to prevent a condition known as bacterial vaginosis (BV).

uterine cycle

The endometrium of the uterus has a similar cycle (see Fig. 29-5), the uterine cycle or endometrial cycle. This process prepares the uterus for implantation of an ovum (egg). The uterine cycle is controlled by the ovarian cycle and will vary, depending on whether or not fertilization of the ovum occurs. The three phases of the uterine cycle are the proliferative phase, the secretory phase, and the menstrual (menstruation) phase

zygote

The fertilized ovum, the , travels to the uterus, where it becomes embedded in the uterine lining, in preparation for further growth. Once the zygote becomes completely embedded in the lining, it is called an embryo. When the fetus is developed enough to survive outside the uterus, the cervix dilates and uterine contractions cause the fetus to be expelled through the vagina

what proximal convulated tubule function

The first portion is the Here, glucose, amino acids, and salts (electrolytes) are actively transported across membranes and returned to the blood. The PCT accomplishes the process of selective reabsorption, because it contains a "brush border," with many villi.

LH

The hypothalamus stimulates the secretion of gonadotropic hormones, which include luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in women

FSH

The hypothalamus stimulates the secretion of gonadotropic hormones, which include luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in women. The main effects of LH and FSH include stimulating both the formation of ova and the secretion of hormones from sex organs. Gonadotropic hormones also stimulate development of secondary female sexual characteristics. The ovaries begin to secrete estrogens, including estradiol, estriol, and estrone. After puberty, the corpus luteum of the ovary produces another hormone, progesterone, which functions primarily during pregnancy.

micturition

The release of urine (urination) from the body is also called voiding, Involuntary micturition is called urinary incontinence; inability to void is urinary retention. The verb "to void" means "to vacate" or "make empty." Urine flows from the collecting tubules into the renal pelvis, down the ureters, and collects in the bladder. As urine distends the bladder, nerve endings in the bladder walls are stimulated. The brain interprets the message of fullness and the nervous system stimulates internal and external sphincter muscles controlling the urethral opening to relax. Since the external sphincter is controlled voluntarily, the person can control voiding. Many conditions can cause urinary incontinence. Chapter 89 describes urinary disorders and Chapter 90 describes male urinary disorders, in conjunction with reproductive disorders.

renal artery function

The kidneys receive their generous blood supply from the renal arteries and because they branch directly from the abdominal aorta, renal blood is highly oxygenated (see Fig. 22-4). The renal arteries diverge, forming smaller arteries, until they become the afferent arterioles supplying blood to the glomeruli (see Fig. 27-3). Glomerular blood pressure is higher than in most capillaries (60 mm Hg vs. 30 mm Hg), necessary for the formation of glomerular filtrate (discussed later). Efferent arterioles carry blood away from glomeruli. First, they branch off to form peritubular capillaries, surrounding the convoluted tubules (see Fig. 27-3). These capillaries drain into a system of veins (the interlobular, arcuate, and interlobar veins), ending at the renal vein, which empties into the inferior vena cava to return blood to the heart (Fig. 27-6). The two sites of capillary exchange in the kidneys are the glomeruli and peritubular capillaries. The glomeruli begin urine formation; peritubular capillaries carry substances from the kidneys back to the circulatory system for reuse and also nourish the renal tissue itself.

composition of urine what's excreted

The kidneys secrete fluids and dissolved substances, stored in the urinary bladder, and excreted as urine through the urethra. Many factors influence the quantity of urine, including the amount of fluid and salt a person takes in, perspiration, hemorrhage, blood pressure, vomiting, external temperature, drugs, fever, and various diseases. Urine is initially a clear yellow liquid, with a characteristic odor. Several factors influence urine color. Amber or dark yellow urine may indicate a decrease in water and dehydration; some foods and drugs influence urine color. Urine may become cloudy (turbid) or have an ammonia-like odor, if left sitting. Normally, urine has an acidic pH, but this can vary. Chapter 52 discusses the concept of specific gravity (the relationship between that urine and pure water) and its measurement. The specific gravity of pure water is 1.000; normal urine is only slightly concentrated, with a specific gravity of about 1.010 to 1.025. A higher-specific gravity indicates concentrated urine, the result of dehydration or urinary retention. Lower-specific gravity indicates dilute urine, secondary to overhydration or a physical disorder. When kidneys are diseased, they are often unable to concentrate urine; therefore, specific gravity remains dilute. Certain wastes are always present in urine, but analysis indicates the presence of abnormal substances. The composition of normal urine is about 95% water (a solvent) and 5% solutes. Solutes may be composed of the following: • Nitrogenous waste products from breakdown of proteins; common protein wastes are urea, uric acid, and creatinine • Excess minerals from the diet, such as sodium, potassium, chloride, calcium, sulfur, magnesium, ammonium, and phosphate • Toxins and certain drug metabolites• Hormones (especially those related to the person's sex); male sperm cells • Pigments caused by certain foods or drugs may also appear; urobilinogen In case of disease or malfunction, abnormal products, such as blood, 1181 glucose, pus, large amounts of bacteria, casts, ketone bodies, bile, and albumin (protein), may be present. Urine is normally sterile (free from microorganisms); nonsterile urine implies disease or infection. Key Concept Kidney transplants are the most frequently performed type of organ transplant. They were also the first organ transplant to be successful, with many recipients surviving 35 years or more.

nephron

The kidneys' major role is the filtration of water-soluble wastes out of the blood. Nephrons (from Greek: nephros = kidney) are the functional units of the kidney. Nephrons form urine; the other structures of the urinary system expel urine. More than 1 million microscopic nephrons are in each kidney, but humans can survive using only one third of their nephrons Most of each nephron is in the renal cortex (superficial and midcortical nephrons), except for a small tube in the medulla. Juxtamedullary nephrons are those near the medulla. At one end of each microscopic nephron is a knotted cluster, tuft, or loop of capillaries, the glomerulus (plural: glomeruli; from Latin glomus = ball), which are supported by a thin membrane, the mesangium (see Fig. 27-4B). The glomerulus is partially enclosed in a funnel-shaped structure, Bowman's capsule (Bowman's space, glomerular capsule) (see Fig. 27-3), which pressure- filters large solutes out of the blood through pores. The glomerulus and Bowman's capsule together are known as the renal corpuscle (or malpighian corpuscle), which is the beginning of the nephron. Because the efferent arteriole (leaving the glomerulus) is smaller in diameter than the afferent arteriole, the pressure in the glomerulus is increased, assisting in pressure filtration of molecules out of plasma.

endometrium

The mucous layer, the forms the maternal portion of the placenta during pregnancy. The uterus receives the fertilized ovum and provides housing and nourishment for a fetus. At the end of gestation, the uterus expels the fetus (delivery). Pregnancy, labor, and delivery are discussed in Unit 10. In some cases, a couple has difficulty conceiving a child

Loop of Henle

The next portion of the convoluted tubule is the (nephron loop), the major function of which is to concentrate salts by reabsorbing water (by osmosis) reabsorbs water and additional electrolytes

erthropoietin

The second hormone produced by the kidneys, stimulates the stem cells in red bone marrow to increase formation of red blood cells (RBCs, erythrocytes). This is known as erythropoiesis. EPO is secreted when hypoxia (impaired oxygenation) is recognized, usually the result of injury, or cardiac or pulmonary disorders. (Erythropoietin is produced in the liver in the fetus.)

Scrotum

The two testes are supported and protected in a sac-like structure, the , suspended behind the base of the penis. The external appearance of the scrotum varies, depending on environmental conditions and muscle contraction. The scrotum regulates the temperature of the testes; thecremasteric muscles involuntarily contract and tighten the spermatic cord to bring the testicles closer to the body as external temperature lowers (the cremasteric reflex). This reflex may also occur in response to severe danger or during sexual intercourse. The temperature of the testes (35°C or 95°F) is lower than internal body temperature (normally 37°C or 98.6°F) to facilitate sperm production. Exposure to increased temperature over a period of time can impair spermatogenesis (sperm production) in the testes. Tight-fitting clothing also can cause decreased sperm production, due to increased heat.

vasectomy

The two vas deferens or ductus deferentia are ligated (tied) and cut in the male sterilization procedure, vasectomy. This operation does not affect erection or ejaculation; it just prevents sperm from passing.

Bartholin gland

The vestibule floor contains Bartholin's glands (greater vestibular glands), which lubricate the vagina. (If the openings of these glands become obstructed, Bartholin's cysts can result.) The clitoris is a small erectile structure that responds to sexual stimulation. The structure of the clitoris is similar to that of the penis. Both become engorged with blood as a result of sexual excitement,and stimulation of either structure often leads to orgasm. The female (obstetrical) perineum is the space between the vaginal orifice and the anus. It is made up of strong muscles that act as sling-like supports for pelvic organs.

kidney function

Two kidneys extract wastes from the blood, balance body fluids, and form urine are two reddish-brown, bean-shaped organs in the small of the back, at the lower edge of the ribs on either side of the vertebral column (Fig. 27-1). They are each about the size of a human fist (about 4 in [10 cm] long, 2 in [5 cm] wide, and 1 in [2.5 cm] thick). On top of each kidney lies an adrenal (suprarenal) gland (ad = near, over); these influence blood pressure, as well as sodium and water retention in the kidneys. (See Chapter 20 for endocrine functions.) are retroperitoneal (behind the peritoneum), allowing kidney surgery to be performed from the back, without entering the abdominal cavity. The right kidney is slightly lower than the left, making space for the liver. A person can easily live with one kidney. Ren- is the prefix related to kidneys; the descriptive term is renal. The word element referring to the kidney is nephr(o-). are extremely vascular (heavily supplied with blood vessels), to provide blood supply for filtering and waste removal. Approximately 10% of the body's blood circulates through the kidneys daily. Each kidney is surrounded by perinephric (around the kidney) fat, and is surrounded by a fibrous capsule, which continues downward, forming the outer layer of the ureter covering. The fatty pads, plus renal fascia, anchored to surrounding tissues, help hold the kidneys in place. On 1155 the medial surface of each kidney (toward the middle of the body) is an indented area called the hilum, a notch through which blood vessels, nerves, and the ureter enter. The kidneys can precisely regulate and adjust electrolyte levels. Body fluid volume is regulated by management of sodium chloride (NaCl) levels. The kidneys balance pH in the blood, the body fluids, and within body tissues by eliminating acids directly into the urine or by excreting acids bound to chemical buffers. These buffers change strong acids into weaker acids, enabling the kidneys to excrete large amounts of acid without dramatically altering (or lowering) urine pH. (However, urine is still 1,000 times more acidic than blood.) Other major functions of the kidneys include hormonal secretion of renin and erythropoietin, and activation of vitamin D. If the kidney is cut in half longitudinally, it is clearly divided into two parts: the outside, the cortex, and the inner portion, the medulla ("middle"). The renal cortex is the outer reddish-brown part of the kidney that extends from the outside of the kidney (renal capsule) to the bases of the renal pyramids and into the spaces between them (Fig. 27-2). The renal corpuscles (glomeruli and Bowman's capsules) and the proximal and distal portions of the convoluted tubules make up the major portion of the renal cortex (see "Nephrons" section and Fig. 27-3). major role is the filtration of water-soluble wastes out of the blood. Nephrons (from Greek: nephros = kidney) are the functional units of the kidney. Nephrons form urine; the other structures of the urinary system expel urine. More than 1 million microscopic nephrons are in each kidney, but humans can survive using only one third of their nephrons. Waste removal (e.g., urea) • Regulation of electrolytes by excretion and reabsorption (particularly sodium, potassium, calcium) • Secretion of specific hormones• Maintenance of acid-base, fluid, and electrolyte balance • Conversion of vitamin D to a useful form

oofacytes

a cell in an ovary which may undergo meiotic division to form an ovum.

development of oomphoscyte sequence

oogonia, primary oocyte, secondary follicle, graphian follicle, ovam

renal medulla

contains the remainder of the renal tubules, loops of Henle, and collecting tubules. These tubules form a number of cone- shaped structures, the renal pyramids. These 8-12 pyramids are arranged so their bases are on the outside near the renal cortex. The tips (renal papillae) of the renal pyramids point medially toward the renal pelvis, a funnel-shaped basin at the upper end of the ureter. Urine flows from the collecting tubules through the pyramids and into cup-like extensions of the renal pelvis, the calyces (singular: calyx). Table 27-1 summarizes key information.

HRT

hormone replacement therapy (estrogen and progesterone) is the replacement of female sex hormones oestrogen and progesterone in women to control symptoms of the menopause.

secondary sex characteristics of male

including the typical male beard, pubic, and axillary hair, as well as increased body hair. Unique musculature develops; the shoulders become broader and the hips remain narrow. The voice deepens and the "Adam's apple" (unique to the male) develops in the anterior throat. Testosterone also maintains the functioning of male accessory organs and stimulates protein anabolism. As a result, a man usually has larger and stronger musculature than a woman.

specific gravity

is a measure of the concentration of solutes in the urine. It measures the ratio of urine density compared with water density and provides information on the kidney's ability to concentrate urine. A urinary specific gravitymeasurement is a routine part of urinalysis.

3 points of attachment for bladder

is normally sterile; it is a hollow muscular sac which, when empty, lies behind the symphysis pubis and stores urine (see Fig. 27-1). When full, the bladder may extend well up into the abdominal cavity. The bladder is composed of transitional epithelium and lined with mucous membrane. The trigone (vesical trigone) is a triangular area on the floor of the bladder that does not expand. The three points of this triangle are the attachments of the two ureters and the urethra. Bladder capacity varies, but most people experience the desire to void (empty the bladder), when it fills to 200 to 400 mL (in 2 to 5 hours), although the maximum capacity is about 1,000 mL. Inability to void is called (urinary) retention. The muscles in the bladder walls distend (stretch and expand) as it fills with urine; they contract as the bladder empties. An involuntaryinternal sphincter (circular muscle) relaxes as it senses the impulse to void, an external sphincter is under conscious control. To initiate urination, the detrusor muscle contracts and the external sphincter relaxes. Word elements relating to the bladder are vesic(o)- and cyst(o)-.

pathway of urine

kidney, ureter, bladder, urethra Afferent arteriole → glomerulus and Bowman's capsule → PCT → loop of Henle (descending limb—permeable to water; impermeable to salts, and ascending limb —impermeable to water, pumps sodium out of filtrate) → distal convoluted tubule (with parathyroid hormone, reabsorbs calcium, excretes phosphate; with aldosterone, reabsorbs sodium, excretes potassium; also regulates pH with hydrogen and ammonium) → JGA (end of nephron) → collecting duct system

chronic kidney failure

kidneys do not function properly resulting in inadequate erythropoietin production, usually resulting in anemia

Aldosterone

promotes sodium and water retention, increasing blood volume, again elevating blood pressure. A mineralocorticoid hormone, aldosterone responds to blood levels high in potassium or low in sodium. In these cases, aldosterone stimulates excretion of potassium ions and reabsorption of sodium ions. Sodium ions return to the blood, water follows the salt via osmosis, and potassium ions are excreted in urine is very important in blood pressure regulation. If blood pressure or circulating blood volume falls too low, cells of the JGA secrete renin into the bloodstream. This activates the renin-angiotensin-aldosterone (RAA) mechanism, to raise blood pressure (Fig. 27-5). Renin stimulates the formation of angiotensin I, which, in the presence of a converting enzyme,

glomalular filtration

removes particles from a solution by allowing the solvent to pass across a barrier, much like a sieve. The barrier allows certain solutes, which are small enough, to pass through. Larger solutes remain in the original solution, because they are too large to pass through the barrier (see Chapter 17). Glomerular filtration denotes the movement of wastes across glomeruli into Bowman's capsule (see Fig. 27-6). Blood enters the glomerulus and flows through smaller and smaller vessels. This increases the pressure (described below) within the vessels, and forces a fluid (glomerular filtrate) out of the glomerulus into Bowman's capsule. This fluid resembles plasma, but it contains no blood cells and almost no protein. (Large protein molecules and RBCs are filtered out and cannot pass into the glomerulus.) Glomerular filtrate contains water, glucose, urea, creatinine, and numerous electrolytes. The amount of filtrate formed in all glomeruli of both kidneys per minute is called the glomerular filtration rate (GFR). Normal GFR in an adult is about 125 mL/min (about 180 L/day). Glomerular filtration depends on relative pressures. The diameter of the afferent (entering) arteriole is greater than that of the efferent (leaving) arteriole, making it easier for blood to enter the glomerulus than to leave it. (Remember that glomerular blood pressure is much higher than that of other body capillaries. Consequently, the high pressure continually filters [squeezes] wastes from the glomerulus into Bowman's capsule.) In the kidneys, specific forces promote, and other forces resist, filtration of waste products into the kidneys. In a healthy person, forces enabling filtration of blood to occur in the glomerulus will win by a small margin, the net filtration pressure; usually about 10 mm Hg. 1175

Kidney location

small of the back at the lower edge of ribs on either side of the veterbral column

testosterone function

stimulates development of male sex characteristics; stimulates male sex drive and regulates sperm productionThe major androgen is ; its production is stimulated by ICSH. During puberty, male glandular development becomes very active

location of ovaries

the brim of the pelvis, one on either side of the uterus

estrogen and progesterone

the ovaries begin to secrete estrogens, including estradiol, estriol, and estrone. After puberty, the corpus luteum of the ovary produces another hormone, progesterone, which functions primarily during pregnancy. The pubescent girl exhibits many changes as a result of estrogen production. Characteristic secondary sexual characteristics of the female include a smaller stature, higher percentage of body fat, pubic and axillary hair, and development of breasts. The female pubic arch (subpubic angle) of the pelvis and hip structure is wider than that of the male, to facilitate childbirth. Sweat glands become more active. Although voice changes are not as marked as those in a boy, the voice does deepen and mature in tone and quality. As glands of reproduction become active, menstruation occurs. All female secondary sex characteristics depend on secretion ofestrogens and progesterone. The gonads (sex organs) in women are the ovaries, which produce female gametes or ova (singular: ovum) and secrete female sex hormones (estrogens). Although several estrogens exist (the primary one is estradiol), the entire classification, estrogen, commonly refers to all female sex hormones collectively. The ovaries are two almond-shaped glands, each about 1.5 in (3.8 cm) in length, located within the brim of the pelvis, one on either side of the uterus (see Fig. 29-1). (The combining form relating to ovary is oophor/o-.)

ovarian cycle

the ovum matures and is expelled from the ovary into the oviduct. The maturation of another ovum is then withheld until the next cycle. The three phases of the ovarian cycle are the follicular phase, ovulation, and the luteal phase (see Fig. 29-5). Table 29-1 discusses the hormones and phases of the ovarian cycle.

tubular secretion kidney

the process by which substances move from blood into the urine (opposite of reabsorption), occurs by active or passive transport (see Fig. 27-7). Molecules secreted in peritubular capillaries (see Figs. 27- 3 and 27-6) move into tubular cells, then into the tubular lumen. Secretions into urine include end products of metabolism and other body processes, such as ammonia (NH3), bile pigments, and urea, along with metabolites (end products) of drugs. Ions, such as hydrogen (H+) and potassium (K+), are also subject to tubular secretion. (Acid-base regulation by the kidneys depends on tubular secretion of hydrogen ions.)

function of urethra

the tube through which urine passes to the outside of the body, opens onto the bladder wall. In men, the urethra is about 8 in (20 cm) long (see Fig. 27-1). It passes through the prostate gland, where two ducts from the male sex glands join it, and then through the length of the penis. The woman's urethra is short, about 1.5 in (3.8 cm) long, opens to the outside at the urinary meatus or urinary canal, and is the passageway for urine only (see Fig. 27-2). In the male, the urethra serves as the passageway for both urine and sperm (male sex cells). Protective muscles prevent the passage of both at the same time.