Chapter 22: The Endocrine System

Thyroid hormones regulate:

- (1) oxygen use and basal metabolic rate, (2) cellular metabolism, and (3) growth and development. A few cells called parafollicular cells, or C cells, may be embedded within a follicle or lie between follicles. - They produce the hormone calcitonin, which helps regulate calcium homeostasis.

Acidophils

- (somatotrophs and lactotrophs) make up about 40 percent of anterior pituitary cells, stain red with acidic dyes, and also contain secretory granules.

Basophils

- (thyrotrophs, gonadotrophs, and corticotrophs) make up about 10 percent of anterior pituitary cells, stain blue with basic dyes, and contain secretory granules. These cells should not be confused with white blood cells of the same name.

Seasonal affective disorder

- A type of depression that afflicts some people during the winter months, when day length is short. - Thought to be due, in part, to overproduction of melatonin. - Full‐spectrum bright‐light therapy—repeated doses of several hours of exposure to artificial light that is as bright as sunlight—provides relief for some people. - Three to six hours of exposure to bright light also appears to speed recovery from jet lag, the fatigue suffered by travelers who quickly cross several time zones.

Anterior pituitary

- AKA adenohypophysis (ad′‐ē‐nō‐hī‐POF‐i‐sis; adeno‐=gland; hypophysis=undergrowth), secretes hormones that regulate a wide range of bodily activities, from growth to reproduction. - Release of anterior pituitary hormones is stimulated by releasing hormones and suppressed by inhibiting hormones from the hypothalamus

The ovaries are located within the ____________ of the body.

- Abdominal/ pelvic cavity

Ectoderm

- About three weeks after fertilization, the pituitary gland (hypophysis) begins to develop from two different regions of the ectoderm. - Posterior pituitary (neurohypophysis) is derived from an outgrowth of ectoderm called the neurohypophyseal bud, located on the floor of the hypothalamus. - The infundibulum, also an outgrowth of the neurohypophyseal bud, connects the posterior pituitary to the hypothalamus. - The anterior pituitary (adenohypophysis) is derived from an outgrowth of ectoderm from the roof of the mouth called the hypophyseal pouch or Rathke's pouch. --> The pouch grows toward the neurohypophyseal bud and eventually loses its connection with the roof of the mouth.

Neurosecretory cells

- Above the optic chiasm are clusters of specialized neurons. - They synthesize the hypothalamic releasing and inhibiting hormones in their cell bodies and package the hormones inside vesicles, which reach the axon terminals by axonal transport.

Which of the following structures is affected by releasing hormones produced by the hypothalamus?

- Adenohypophysis

Which endocrine gland is shown in the diagram?

- Adrenal

Mesoderm

- Adrenal cortex is derived from intermediate mesoderm from the same region that produces the gonads. - Endocrine tissues that secrete steroid hormones all are derived from mesoderm. The adrenal medulla is derived from ectoderm from neural crest cells that migrate to the superior portion of the kidney. - Recall that neural crest cells also give rise to sympathetic ganglia and other structures of the nervous system.

Endocrine system

- All endocrine glands and hormone‐secreting cells constitute the endocrine system.

Cells of the pancreas which produce glucagon are

- Alpha cells

Hypophoseal portal system

- Also referred to as the hypothalamic‐hypophyseal portal system, blood flows from capillaries in the hypothalamus into portal veins that carry blood to capillaries of the anterior pituitary.

Anterior pituitary

- Anterior pituitary (anterior lobe) accounts for about 75 percent of the total weight of the gland and is composed of epithelial tissue. It develops from an outgrowth of ectoderm called the hypophyseal (Rathke's) pouch in the roof of the mouth. - Consists of two parts in an adult: The pars distalis is the larger bulbar portion, and the pars tuberalis (PARS too‐be‐RAL‐is) forms a sheath around the infundibulum.

Antidiuretic

- Antidiuretic is a substance that decreases urine production. - ADH causes the kidneys to return more water to the blood, thus decreasing urine volume. - In the absence of ADH, urine output increases more than tenfold, from the normal 1-2 liters to about 20 liters a day. - Drinking alcohol often causes frequent and copious urination because the alcohol inhibits secretion of ADH. ADH also decreases the water lost through sweating and causes constriction of arterioles, which increases blood pressure. The other name for this hormone, vasopressin, reflects its effect on blood pressure.

Pars intermedia

- Atrophies during fetal development and ceases to exist as a separate lobe in adults (see Figure 22.8b). However, some of its cells migrate into adjacent parts of the anterior pituitary, where they persist.

Superior hypophyseal arteries

- Branches of the internal carotid arteries, bring blood into the hypothalamus. - At the juncture of the median eminence of the hypothalamus and the infundibulum, these arteries divide into a capillary network called the primary plexus of the hypophyseal portal system. - From the primary plexus, blood drains into the hypophyseal portal veins that pass down the surface of the infundibulum. - In the anterior pituitary, the hypophyseal portal veins divide again and form another capillary network called the secondary plexus of the hypophyseal portal system. - Hypophyseal veins drain blood from the anterior pituitary.

Thyroid gland

- Butterfly‐shaped thyroid gland is located just inferior to the larynx (voice box); the right and left lateral lobes lie on either side of the trachea. - Connecting the lobes is a mass of tissue called an isthmus (IS‐mus) that lies anterior to the trachea. About 50 percent of thyroid glands have a small third lobe called the pyramidal lobe. It extends superiorly from the isthmus.

Which of the following is a function of CCK?

- Causes feeling of fullness after eating

The majority of the adrenal gland by weight that develops from mesoderm is

- Cortex

Which of the following types of cells produces ACTH?

- Corticotrophs

Which of the following pancreatic cells secrete somatostatin?

- D cells

Posterior pituitary (neurohypophysis)

- Does not synthesize hormones, it does store and release two hormones. - It consists of pituicytes and axon terminals of hypothalamic neurosecretory cells. - Cell bodies of the neurosecretory cells are in the paraventricular and supraoptic nuclei of the hypothalamus; their axons form the hypothalamohypophyseal tract, which begins in the hypothalamus and ends near blood capillaries in the posterior pituitary gland. - Different neurosecretory cells produce two hormones: oxytocin and antidiuretic hormone, also called vasopressin.

From which layer of the embryo do the different parts of the pituitary gland form?

- Ectoderm

The development of the endocrine system in the embryo is normally from this/these layer(s).

- Ectoderm, mesoderm, endoderm, chorionic and amnionic

Which is the term for a gland that secretes its product into the interstitial fluid?

- Endocrine

Which of the hormones listed below is/are produced by the adrenal gland in the specific region indicated in the figure?

- Epinephrine/ norepinephrine

Which of the choices listed below are hormones produced by the ovaries?

- Estrogens, inhibin, progesterone, relaxin

Ovaries

- Female gonads, called the ovaries, are paired oval bodies located in the pelvic cavity. - The ovaries produce female sex hormones called estrogens and progesterone. Along with the gonadotropic hormones of the pituitary gland, the sex hormones regulate the female reproductive cycle, maintain pregnancy, and prepare the mammary glands for lactation. - These hormones are also responsible for the development and maintenance of female secondary sexual characteristics. In addition, the ovaries produce inhibin, a hormone that inhibits secretion of follicle‐stimulating hormone (FSH) from the anterior pituitary. - During pregnancy, the ovaries and placenta produce a hormone called relaxin (RLX), which increases the flexibility of the pubic symphysis during pregnancy and helps dilate the uterine cervix during labor and delivery.

In order for the gonads to respond to the presence of follicle-stimulating hormone, the cells of the gonads must

- Have receptors for follicle- stimulating hormone

These chemicals are released into the interstitial fluid and the blood in very small amounts to impact tissue in other locations.

- Hormones

This hormone has been used by athletes to increase muscle mass and reverse or slow the aging process of muscular atrophy.

- Human growth

Decreased production of which of the following, with age, is one cause of muscle atrophy as aging proceeds?

- Human growth hormone (hGh)

Major hormones secreted by five types of anterior pituitary cells

- Human growth hormone, or somatotropin, is secreted by cells called somatotrophs. Human growth hormone in turn stimulates several tissues to secrete insulin- like growth factors, hormones that stimulate general body growth and regulate various aspects of metabolism. - Thyroid‐stimulating hormone, or thyrotropin, which controls the secretions and other activities of the thyroid gland, is secreted by cells called thyrotrophs. - Follicle‐stimulating hormone and luteinizing hormone are secreted by cells called gonadotrophs. FSH and LH both act on the gonads: They stimulate secretion of estrogens and progesterone and the maturation of oocytes in the ovaries, and they stimulate secretion of testosterone and sperm production in the testes. - Prolactin, which initiates milk production in the mammary glands, is released by cells called lactotrophs. - Adrenocorticotropic hormone, or corticotropin, which stimulates the adrenal cortex to secrete glucocorticoids, is synthesized by cells called corticotrophs. Some corticotrophs also secrete melanocyte‐stimulating hormone.

Portal system

- Hypothalamic hormones that release or inhibit anterior pituitary hormones reach the anterior pituitary through a portal system.

Which of the following is an effect of PTH?

- Increased bone resorption

What happens to the concentration of melatonin in the blood during sleep?

- Increases

The hormone that inhibits the secretion of FSH from the anterior pituitary is

- Inhibin

Adrenal medulla

- Inner region of the adrenal gland, the adrenal medulla, is a modified sympathetic ganglion of the autonomic nervous system (ANS). - Develops from the same embryonic tissue as all other sympathetic ganglia (embryonic neural crest tissue), but its cells lack axons and form clusters around large blood vessels. --> Rather than releasing a neurotransmitter, the cells of the adrenal medulla secrete hormones. The hormone‐producing cells, called chromaffin cells, are innervated by sympathetic preganglionic neurons of the greater splanchnic nerve from lower thoracic spinal levels. - Because the ANS controls the chromaffin cells directly, hormone release can occur very quickly.

In the figure shown, what is secreted by the indicated cell?

- Insulin

What hormone is release from beta cells of the pancreatic islets?

- Insulin

The endocrine system is composed of glands that secrete

- Into interstitial fluids

How will the sensitivity of a target cell's response to a hormone change after down-regulation?

- It will decrease

Which organ secretes renin, erythropoietin, and calcitiol?

- Kidneys

What hormone, released by adipose tissue, suppresses appetite?

- Leptin

Which of the following hormones functions to suppress appetite and may increase the activity of FSH and LH?

- Leptin

Activity in the organ labeled E is impacted by ____________. (Testes)

- Luteinizing hormone, follicle stimulating hormone

Chromophobes

- Make up about 50 percent of anterior pituitary cells and have little affinity for basic or acidic dyes. They have few or no secretory granules and do not secrete hormones. They are believed to be basophils or acidophils that have already released their granules.

Testes

- Male has two oval gonads, called testes, that produce testosterone, the primary androgen. - Testosterone stimulates descent of the testes before birth, regulates production of sperm, and stimulates the development and maintenance of male secondary sexual characteristics such as beard growth. - The testes also produce inhibin, which inhibits secretion of FSH

Which of the following contributes to setting the body's biological clock?

- Melatonin

The adrenal cortex develops from ________ whereas the adrenal medulla develops from _________.

- Mesoderm; ectoderm

Hormones

- Molecules that alter the physiological activity of other cells in the body. - From the interstitial fluid, hormones move into blood capillaries and are carried by the blood throughout the body. - Very small amount of most hormones are required in most cases to produce a response, so circulating levels typically are low. - Affects only certain target cells. Hormones, like neurotransmitters, influence their target cells by chemically binding to specific protein receptors. Only the target cells for a given hormone have receptors (hormone receptors) that bind and recognize that hormone.

Chief principal cells

- More numerous cells are called chief (principal) cells and produce parathyroid hormone (PTH), or parathormone. - Function of the other type of parathyroid epithelial cell, called an oxyphil cell, is unknown in a normal parathyroid gland. - Presence clearly helps to identify the parathyroid gland histologically due to its unique staining characteristics. - In a cancer of the parathyroid glands, oxyphil cells secrete excess PTH.

All of these organs include tissues that have endocrine functions except which?

- NONE OF THESE CHOICES (none being heart, stomach, kidney)

The thyroid gland is located in the _____________ of the body.

- Neck

These two systems coordinate functions of the body

- Nervous and endocrine

Only certain cells in the body are target cells for the steroid hormone aldosterone. Which of the following is the best explanation for why these are the only cells that respond to this hormone?

- Only target cells contain receptors for aldosterone

As an individual ages, which endocrine gland decreases in size?

- Ovaries

The production (synthesis) of which of the following does NOT occur in the pituitary gland?

- Oxytocin (OT)

Calcitriol and PTH

- PTH decreases blood HPO42− level and increases blood Ca2+ and Mg2+ levels. With respect to blood Ca2+ level, PTH and calcitonin are antagonists; that is, they have opposite actions. A third effect of PTH on the kidneys is to promote formation of the hormone calcitriol, the active form of vitamin D.

Hypothalamic activity

- Painful, stressful, and emotional experiences all cause changes in hypothalamic activity. - Hypothalamus controls the autonomic nervous system, regulating body temperature, thirst, hunger, sexual behavior, and defensive reactions such as fear and rage. - Hypothalamus an important regulatory center in the nervous system AND also a crucial endocrine gland.

This gland is both exocrine and endocrine in function.

- Pancreas

Foregut

- Pancreas develops during the fifth through seventh weeks from two outgrowths of endoderm from the part of the foregut that later becomes the duodenum. - The two outgrowths eventually fuse to form the pancreas. The origin of the ovaries and testes is discussed in the section on the reproductive system.

Pancreas

- Pancreas is both an endocrine gland and an exocrine gland. - The pancreas is a flattened organ that measures about 12.5-15 cm (5-6 in.) in length. It is located posterior and slightly inferior to the stomach and consists of a head, a body, and a tail. - Roughly 99 percent of the pancreatic exocrine cells are arranged in clusters called acini, these cells produce digestive enzymes, which flow into the gastrointestinal tract through a network of ducts. - Scattered among the exocrine acini are 1-2 million tiny clusters of endocrine cells called pancreatic islets or islets of Langerhans. - Abundant capillaries serve both the exocrine and endocrine portions of the pancreas.

These glands produce a hormone that helps regulate calcium in the body and is found in the neck area. What are they called?

- Parathyroid glands

Parathyroid gland

- Parathyroid glands develop during the fourth week from endoderm as outgrowths from the third and fourth pharyngeal pouches, which help to form structures of the head and neck.

Which of the following raises blood Ca2+ level?

- Parathyroid hormone

Which gland develops from endoderm?

- Parathyroids

Parathyroid glands

- Partially embedded in the posterior surface of the lateral lobes of the thyroid gland are several small, round masses of tissue. - One superior and one inferior parathyroid gland are attached to each lateral thyroid lobe.

Pituitary gland anatomy

- Pea shaped - Lies in the hypophyseal fossa of the sphenoid bone and attaches to the hypothalamus by a stalk, the infundibulum. - Pituitary gland has two anatomically and functionally separate portions, the anterior pituitary and posterior pituitary.

Diencephalon

- Pineal gland arises during the seventh week as an outgrowth between the thalamus and colliculi of the midbrain from ectoderm associated with the diencephalon.

Posterior pituitary

- Posterior pituitary (posterior lobe) also develops from an ectodermal outgrowth; this one, called the neurohypophyseal bud, is an outgrowth of the neural tube. - Composed of neural tissue and also consists of two parts: the pars nervosa (ner‐VŌ‐sa), the larger bulbar portion, and the infundibulum. - Contains axons and axon terminals of more than 10,000 neurosecretory cells whose cell bodies are located in the supraoptic and paraventricular nuclei of the hypothalamus (see Figure 18.11). The axon terminals in the posterior pituitary gland are associated with specialized neuroglia called pituicytes (pi‐TOO‐i‐sītz). These cells have a supporting role similar to that of astrocytes.

Which hormone increases the flexibility of the pubic symphysis during pregnancy?

- Relaxin

Thymus

- Role in immunity (hormonal role) - Lymphocytes are one type of white blood cell. There are two types of lymphocytes, called T cells and B cells, based on their specific roles in immunity. Hormones produced by the thymus (thymic hormones), called thymosin, thymic humoral factor (THF), thymic factor (TF), and thymopoietin (thī‐mō‐poy‐Ē‐tin), promote the proliferation and maturation of T cells, which destroy foreign substances and microbes.

Thyroid follicles

- Sacs that compose most of thyroid. - The wall of each follicle consists primarily of cells called follicular cells, most of which extend to the lumen (internal space) of the follicle. - When the follicular cells are inactive, their shape is low cuboidal to squamous, but under the influence of TSH they become cuboidal or low columnar and actively secrete hormones. - Follicular cells produce two hormones: thyroxine, which is also called tetraiodothyronine (T4), because it contains four atoms of iodine, and triiodothyronine (T3), which contains three atoms of iodine (collectively referred to as thyroid hormones). -

Endocrine glands

- Secrete their products (hormones) into the interstitial fluid surrounding the secretory cells, rather than into ducts.

Exocrine glands

- Secrete their products (sweat, oil, mucus, and digestive juices) into ducts that carry the secretions into body cavities, into the lumen of an organ, or to the outer surface of the body. - Include sudoriferous (sweat) glands, sebaceous (oil) glands, mucous glands, and digestive glands.

Pineal gland

- Secretes melatonin (Melatonin contributes to the setting of the body's biological clock, which is controlled from the suprachiasmatic nucleus of the hypothalamus. During sleep, levels of melatonin in the bloodstream increase tenfold and then decline to a low level again before awakening). - Is a small endocrine gland attached to the roof of the third ventricle of the brain at the midline - Consists of masses of neuroglia and secretory cells called pinealocytes, which are covered by a capsule formed by the pia mater. Sympathetic postganglionic fibers from the superior cervical ganglion terminate in the pineal gland.

Five different types of cells of the anterior pituitary

- Somatotrophs, thyrotrophs, gonadotrophs, lactotrophs, and corticotrophs

Adrenal cortex

- Subdivided into three different zones, each secrete different hormones. - Outer zone, just deep to the connective tissue capsule, is called the zona glomerulosa. Its cells, which are closely packed and arranged in spherical clusters and arched columns, secrete hormones called mineralocorticoids because they affect metabolism of the minerals sodium and potassium. Aldosterone is a mineralocorticoid. - The middle zone, or zona fasciculata, is the widest of the three zones and consists of cells arranged in long, straight cords. The cells of the zona fasciculata secrete mainly glucocorticoids, primarily cortisol. The glucocorticoids are so named because they affect glucose metabolism. - The cells of the inner zone, the zona reticularis, are arranged in branching cords. They synthesize small amounts of weak androgens, hormones that have masculinizing effects.

Paired adrenal (suprarenal) glands

- Superior poles of kidneys - One of which lies superior to each kidney in the retroperitoneal space, have a flattened pyramidal shape. - Adult, each adrenal gland is 3-5 cm in height, 2-3 cm in width, and a little less than 1 cm thick; it weighs 3.5-5 g, only half its weight at birth. - During embryonic development, the adrenal glands differentiate into two structurally and functionally distinct regions: A large, peripherally located adrenal cortex, representing 80-90 percent of the gland by weight, develops from mesoderm; a small, centrally located adrenal medulla develops from ectoderm.

The adrenal medulla is controlled by a direct connection with the ______________.

- Sympathetic nervous system

This gland in normally found outside the body cavity in the scrotum.

- Testis

Tropic hormones (Tropins)

- These include TSH, ACTH, FSH, and LH. The two gonadotropins, FSH and LH, are tropic hormones that specifically regulate the functions of the gonads.

Which of the items listed below is a/are thymic hormone(s) that assume a role in immunity?

- Thymic factor (TF), thymic humoral factor (THF), thymopoietin, thymosin

In the figure shown, which hormone secreting organ is indicated?

- Thymus

This endocrine gland plays an important role in the early development of the immune system.

- Thymus

Which is the only endocrine structure to store a large quantity of the hormone it produces?

- Thyroid gland

Endoderm

- Thyroid gland develops during the fourth week as a midventral outgrowth of endoderm, called the thyroid diverticulum, from the floor of the pharynx at the level of the second pair of pharyngeal pouches. - The outgrowth projects inferiorly and differentiates into the right and left lateral lobes and the isthmus of the gland.

Epinephrine and norepinephrine

- Two principal hormones synthesized by the adrenal medulla are epinephrine and norepinephrine (NE), also called adrenaline and noradrenaline, respectively. - Epinephrine constitutes about 80 percent of the total secretion of the gland. Both hormones are sympathomimetic—their effects mimic those brought about by the sympathetic division of the ANS. - To a large extent, they are responsible for the fight‐or‐flight response. - Like the glucocorticoids of the adrenal cortex, these hormones help resist stress. - Unlike the hormones of the adrenal cortex, however, the medullary hormones are not essential for life.

Seasonal affective disorder afflicts some people during

- Winter months

Which of the following structures in the adrenal glands secretes mineralocorticoids?

- Zona glomerulosa

Age-related decreases in which of the following hormones leads to a decrease in muscle mass?

- hGh

This structure labeled with the arrow controls many areas of the endocrine system, what is it called?

-Hypothalamus

Two kinds of glands

Exocrine glands and endocrine glands

Pituitary gland

The endocrine system's most influential gland "master gland". Under the influence of the hypothalamus, the pituitary regulates growth and controls other endocrine glands. - Hypothalamus--> major integrating link between the nervous and endocrine systems. It receives input from several other regions of the brain, including the limbic system, cerebral cortex, thalamus, and reticular activating system.