Chapter 9: The Endocrine System 333

Summary
The Endocrine System and Hormone Function— (4) Thyroid-stimulating hormone (TSH): Stimu-
An Overview (pp. 309–312) lates the thyroid gland to release thyroid hor-
mone.
1. The endocrine system is a major controlling system
of the body. Through hormones, it stimulates such (5) Gonadotropic hormones
long-term processes as growth and development, (a) Follicle-stimulating hormone (FSH): Be­­
metabolism, reproduction, and body defense. ginning at puberty, stimulates follicle de­­
velopment and estrogen production by
2. Endocrine organs are small and widely separated in the female ovaries; promotes sperm pro-
the body. Some are part of mixed glands (both duction in the testes.
endocrine and exocrine in function). Others pro-
duce only hormones. (b) Luteinizing hormone (LH): Beginning at
puberty, stimulates ovulation, causes the
3. Nearly all hormones are amino acid–based hor- ruptured ovarian follicle to produce pro-
mones or steroids. gesterone; stimulates testes to produce
4. Endocrine organs are activated to release their hor- testosterone.
mones into the blood by hormonal, humoral, or c. The posterior pituitary stores and releases hypo-
neural stimuli. Negative feedback is important in thalamic hormones on command.
regulating blood hormone levels. (1) Oxytocin: Stimulates powerful uterine con-
5. Bloodborne hormones alter the metabolic activities tractions and causes milk ejection in nursing
of their target organs. The ability of a target organ women.
to respond to a hormone depends on the presence (2) Antidiuretic hormone (ADH): Causes kidney
of receptors in or on its cells to which the hormone tubule cells to reabsorb and conserve body
binds or attaches. water and increases blood pressure by con-
stricting blood vessels. Hyposecretion leads to
6. Amino acid–based hormones act through second diabetes insipidus.
messengers. Steroid hormones can directly influ-
d. Releasing and inhibiting hormones made by the 9
ence the target cell’s DNA or act via second mes-
senger. hypothalamus regulate release of hormones
made by the anterior pituitary. The hypothalamus
The Major Endocrine Organs (pp. 312–327) also makes two hormones that are transported to
the posterior pituitary for storage and later
1. Pituitary gland release.
a. The pituitary gland hangs from the hypothala- 2. The pineal gland, located posterior to the third ven-
mus of the brain by a stalk and is enclosed by tricle of the brain, releases melatonin, which affects
bone. It consists of a glandular portion (anterior sleep/wake cycles.
lobe) and a neural portion (posterior lobe).
b. Except for growth hormone and prolactin, hor- 3. Thyroid gland
mones of the anterior pituitary are all tropic hor- a. The thyroid gland is located in the anterior
mones. throat.
(1) Growth hormone (GH): An anabolic and pro- b. Thyroid hormone, which has two forms (thy-
tein-conserving hormone that promotes total roxine [T4] and triiodothyronine [T3]), is released
body growth. Its most important effect is on from the thyroid follicles when the blood level
skeletal muscles and bones. Untreated hypo- of TSH rises. Thyroid hormone is the body’s
secretion during childhood results in pituitary major metabolic hormone. It increases the rate
dwarfism; hypersecretion produces gigantism at which cells oxidize glucose and is necessary
(in childhood) and acromegaly (in adulthood). for normal growth and development. Lack of
(2) Prolactin (PRL): Stimulates production of iodine leads to goiter. Hyposecretion of thyrox-
breast milk. ine results in cretinism in children and
myxedema in adults. Hypersecretion results
­
(3) Adrenocorticotropic hormone (ACTH): Stim- from Graves’ disease or other forms of­
ulates the adrenal cortex to release its hor- hyperthyroidism.
mones, mainly glucocorticoids.
334 Essentials of Human Anatomy and Physiology

c. Calcitonin is released by parafollicular cells sur- gland. The endocrine islets release insulin and
rounding the thyroid follicles in response to a glucagon to blood.
high blood level of calcium ions. It causes cal- b. Insulin is released when the blood level of glu-
cium to be deposited in bones. cose is high. It increases the rate of glucose
4. Parathyroid glands uptake and metabolism by body cells.
Hyposecretion of insulin results in diabetes mel-
a. The parathyroid glands are four small glands
litus, which severely disturbs body metabo­­
located on the posterior aspect of the thyroid
lism. Cardinal signs are polyuria, polydipsia, and
gland.
polyphagia.
b. A low blood level of calcium stimulates the para-
c. Glucagon, released when the blood level of glu-
thyroid glands to release parathyroid hormone
cose is low, stimulates the liver to release glu-
(PTH). It causes liberation of calcium from bone
cose to blood, thus increasing the blood glucose
to blood. Hyposecretion of PTH results in tetany;
level.
hypersecretion leads to extreme bone wasting
and fractures. 8. Gonads
5. The thymus, located in the upper thorax, functions a. The ovaries of the female release:
during youth but atrophies in old age. Its hormone, (1) Estrogens: Release of estrogens by ovarian
thymosin, promotes maturation of T lymphocytes, follicles begins at puberty under the influ-
important in body defense. ence of FSH. Estrogens stimulate maturation
of the female reproductive organs and female
6. Adrenal glands
secondary sex characteristics. With progester-
a. The adrenal glands are paired glands perched one, they cause the menstrual cycle.
on the kidneys. Each gland has two functional
(2) Progesterone: Progesterone is released from
endocrine portions, the cortex and the medulla.
the ovary in response to a high blood level
b. Adrenal cortex hormones include the following: of LH. It works with estrogens in establishing
(1) Mineralocorticoids, primarily aldosterone, reg­­ the menstrual cycle.
ulate sodium ion (Na+) reabsorption and po- b. The testes of the male begin to produce testos-
tassium ion (K+) secretion by the kidneys. terone at puberty in response to LH stimulation.
Their release is stimulated primarily by low Testosterone promotes maturation of the male
Na+ and/or high K+ levels in blood. reproductive organs, male secondary sex charac-
(2) Glucocorticoids enable the body to resist teristics, and production of sperm by the testes.
long-term stress by increasing the blood glu- c. Hyposecretion of gonadal hormones results in
cose level and depressing the inflammatory sterility in both females and males.
response.
(3) Sex hormones (mainly androgens) are pro- Other Hormone-Producing Tissues and Organs
duced in small amounts throughout life. (pp. 327–331)
c. Generalized hypoactivity of the adrenal cortex 1. Several organs that are generally nonendocrine in
results in Addison’s disease. Hypersecretion can overall function, such as the stomach, small intes-
result in hyperaldosteronism, Cushing’s syn- tine, kidneys, and heart, have cells that secrete hor-
drome, and/or masculinization. mones.
d. The adrenal medulla produces catecholamines
2. The placenta is a temporary organ formed in the
(epinephrine and norepinephrine) in response to
uterus of pregnant women. Its primary endocrine
sympathetic nervous system stimulation. Its cate-
role is to produce estrogen and progesterone,
cholamines enhance and prolong the effects of
which maintain pregnancy and ready the breasts
the “fight-or-flight” (sympathetic nervous system)
for lactation.
response to short-term stress. Hypersecretion
leads to symptoms typical of sympathetic ner-
Developmental Aspects of the Endocrine
vous system overactivity.
System (p. 331)
7. Pancreatic islets
1. Decreasing function of female ovaries at meno-
a. Located in the abdomen close to the stomach, pause leads to such symptoms as osteoporosis,
the pancreas is both an exocrine and endocrine
 Chapter 9: The Endocrine System 335

increased chance of arteriosclerosis, and possible increase in incidence of diabetes mellitus, immune
mood changes. system depression, lower metabolic rate, and, in
some areas, cancer rates.
2. Efficiency of all endocrine glands gradually de-
creases with aging, which leads to a generalized

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Review Questions > Study Area > Practice Tests & Quizzes

Multiple Choice 7. Hormones that regulate mineral (salt) levels include

More than one choice may apply. a. calcitonin.
b. aldosterone.
1. The major endocrine organs of the body
c. atrial natriuretic peptide.
a. tend to be very large organs.
d. glucagon.
b. are closely connected with each other.
c. all contribute to the same function (digestion). 8. Which of the following is given as a drug to reduce
inflammation?
d. tend to lie near the midline of the body.
a. Epinephrine c. Aldosterone
2. Which is generally true of hormones?
b. Cortisol d. ADH
a. Exocrine glands produce them.
9. The element needed for thyroid gland function is
b. They travel throughout the body in the blood.
a. potassium. c. calcium.
c. They affect only non–hormone-producing
organs. b. iodine. d. manganese.
d. All steroid hormones produce very similar
Short Answer Essay
physiological effects in the body.
10. Explain how the nervous and endocrine systems
3. Which of the following hormones is (are) secreted
differ in (a) the rate of their control, (b) the way
by neurons?
in which they communicate with body cells, and 9
a. Oxytocin c. ADH (c) the types of body processes they control.
b. Insulin d. Cortisol
11. Which endocrine organs are actually mixed
4. ANP, the hormone secreted by the heart, has exactly (endocrine and exocrine) glands? Which are purely
the opposite function to this hormone secreted by endocrine?
the outermost zone of the adrenal cortex.
12. Describe the chemical nature of hormones.
a. Epinephrine c. Aldosterone
13. Provide one example for each way endocrine
b. Cortisol d. Testosterone
glands are stimulated to release their hormones.
5. Hormones that act directly or indirectly to elevate
14. Define negative feedback.
the blood glucose level include which of the
following? 15. Explain why not all organs are target organs for all
a. GH hormones.
b. Cortisol 16. Describe the body location of each of the follow­
c. Insulin ing endocrine organs: anterior pituitary, pineal
gland, thymus, pancreas, ovaries, testes. Then, for
d. ACTH
each organ, name its hormones and their effect(s)
6. Hypertension may result from hypersecretion of on body processes. Finally, for each hormone, list
a. thyroxine. c. aldosterone. the important results of its hypersecretion or
hyposecretion.
b. cortisol. d. ADH.
336 Essentials of Human Anatomy and Physiology

17. Name two endocrine-producing glands (or regions) 21. Two hormones are closely involved in the
that are important in the stress response, and regulation of the fluid and electrolyte balance of
explain why they are important. the body. Name them, and explain their effects on
their common target organ.
18. The anterior pituitary is often referred to as the
master endocrine gland, but it too has a “master.” 22. What causes a simple goiter?
What controls the release of hormones by the
23. In general, the endocrine system becomes less
anterior pituitary?
efficient as we age. List some examples of problems
19. What is the most common cause of hypersecretion that elderly individuals have as a result of
by endocrine organs? decreasing hormone production.
20. Name three hormone antagonists of insulin and
one of PTH.

Critical Thinking and Clinical Application Questions

24. A woman with excessive body hair and a deep hypersecreted? What is the cause? What physical
voice shows the outward symptoms of which hor- factors allow you to rule out thyroid problems?
monal dysfunction?
28. What are the possible harmful effects of using ana-
25. The parents of 14-year-old Megan are concerned bolic steroids to increase muscle mass and strength?
about her height because she is only 4 feet tall and
29. Melissa, age 40, comes to the clinic, troubled by
they are both close to 6 feet tall. After tests by their
swelling in her face and unusual fat deposition on
doctor, certain hormones are prescribed for the girl.
her back and abdomen. She reports that she bruises
What is the probable diagnosis? What hormones
easily. Blood tests show an elevated glucose level.
are prescribed, and why might the girl expect to
What is your diagnosis, and which glands might be
reach normal height?
causing the problem?
26. Shannon, a 28-year-old, has been in the first stage
30. Chelsea, a displaced person, is pregnant. She has
of labor for 15 hours. Her uterine contractions are
had no prenatal care, and her diet consists of what
weak, and her labor is not progressing normally.
she is able to salvage from trash cans. What could
Shannon and her doctor desire a vaginal delivery,
you surmise about the PTH level in her blood?
so the physician orders that Pitocin (a synthetic
oxytocin) be infused. What is the effect of this hor- 31. Ryan had symptoms of excessive secretion of PTH
mone? (a high blood calcium ion level), and his physicians
were certain he had a parathyroid gland tumor. Yet
27. Mr. Flores brings his wife to the clinic, concerned
when surgery was performed on his neck, the sur-
about her nervousness, heart palpitations, and
geon could not find the parathyroid glands at all.
excessive sweating. Tests show hyperglycemia and
Where should the surgeon look next to find the
hypertension. What hormones are probably being
tumorous parathyroid gland?