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CHAPTER
16
The Endocrine System
Objectives
The Endocrine System: An Overview
1. Indicate important differences between hormonal and neural controls of body
functioning.
Hormones
4. Describe how hormones are classified chemically.
The Pituitary Gland and Hypothalamus
8. Describe structural and functional relationships between the hypothalamus and the
pituitary gland.
Major Endocrine Glands
11. Describe the effects of the two groups of hormones produced by the thyroid gland.
12. Follow the process of thyroxine formation and release.
13. Indicate the general functions of parathyroid hormone.
Hormone Secretion by Other Organs
18. Name a hormone produced by the heart.
Developmental Aspects of the Endocrine System
21. Describe the effects of aging on endocrine system function.
Suggested Lecture Outline
I. The Endocrine System: An Overview (pp. 592–593; Fig. 16.1)
A. Endocrinology is the scientific study of hormones and the endocrine organs (p. 592;
Fig. 16.1).
1. Hormones are chemical messengers that are released to the blood and elicit target cell
effects after a period of a few seconds to several days.
B. Autocrines are local chemical messengers that act on the same cells that secrete them,
while paracrines are local chemical messengers that act on neighboring cells, rather than
the cells releasing them (pp. 592–593).
II. Hormones (pp. 593–598; Figs. 16.2–16.4)
A. The Chemistry of Hormones (p. 593)
1. Most hormones are amino acid based, but gonadal and adrenocortical hormones are
B. Mechanisms of Hormone Action (pp. 593–595; Figs. 16.2–16.3)
1. Cells that have receptors for a given hormone are called target cells.
4. Lipid-soluble hormones (steroids and thyroid hormone) diffuse into the cell, where
they bind to intracellular receptors, migrate to the nucleus, and activate specific genes.
6. Direct gene activation occurs when a lipid-soluble hormone or thyroid hormone binds
to an intracellular receptor, which activates a specific region of DNA, causing the
production of mRNA and initiation of protein synthesis.
C. Target Cell Specificity (pp. 595–596)
1. Cells must have specific membrane or intracellular receptors to which hormones can
bind.
D. Control of Hormone Release (pp. 596–597; Fig. 16.4)
1. Most hormone synthesis and release is regulated through negative feedback
mechanisms.
2. Endocrine gland stimuli may be humoral, neural, or hormonal.
a. Critical ions or nutrients that act as stimuli controlling the secretion of hormones
are humoral stimuli.
3. Nervous system modulation allows hormone secretion to be modified by hormonal,
humoral, and neural stimuli in response to changing body needs.
E. Half-Life, Onset, and Duration of Hormone Activity (p. 598)
1. The concentration of a hormone reflects its rate of release and the rate of inactivation
3. Target organ response and duration of response vary widely among hormones.
F. Interaction of Hormones at Target Cells (p. 598)
1. Permissiveness occurs when one hormone cannot exert its full effect without another
hormone being present.
III. The Pituitary Gland and Hypothalamus (pp. 598–606; Figs. 16.5–16.8;
Table 16.1)
A. The pituitary gland is situated in the sella turcica of the skull, and is connected to the
brain via the infundibulum (p. 598; Fig. 16.5).
B. The pituitary has two lobes: the posterior pituitary, or neurohypophysis, which is neural
in origin, and the anterior pituitary, or adenohypophysis, which is glandular in origin
(pp. 598–599; Fig. 16.5).
C. The Posterior Pituitary and Hypothalamic Hormones (pp. 599–601; Table 16.1)
D. Anterior Pituitary Hormones (pp. 601–606; Figs. 16.5–16.8; Table 16.1)
1. The anterior pituitary produces six hormones, four of which are tropic hormones that
regulate secretion of other hormones, as well as a prohormone.
a. Pro-opiomelanocortin (POMC) is a prohormone that can be split into adrenocorti-
cotropic hormone, two natural opiates, and melanocyte-stimulating hormone.
f. Prolactin stimulates the gonads and promotes milk production in humans.
IV. The Thyroid Gland (pp. 606–610; Figs. 16.9–16.11; Table 16.2)
A. The thyroid gland consists of hollow follicles with follicular cells that produce
thyroglobulin and parafollicular cells that produce calcitonin (pp. 606–607; Fig. 16.2).
B. Thyroid hormone consists of two amine hormones, thyroxine (T4) and triiodothyronine
(T3), that act on all body cells to increase basal metabolic rate and body heat production
(pp. 607–610; Figs. 16.10–16.11; Table 16.2).
1. The thyroid can store a three to four months’ supply of thyroid hormone.
2. Synthesis of thyroid hormone involves several steps:
C. Calcitonin, secreted by C cells of the thyroid, is a peptide hormone that lowers blood
calcium by inhibiting osteoclast activity, stimulating Ca++ uptake and incorporation of
Ca++ into the bone matrix (p. 610).
V. The Parathyroid Glands (pp. 610–611; Figs. 16.12–16.13)
VI. The Adrenal (Suprarenal) Glands (pp. 611–616; Figs. 16.14–16.17; Table 16.3)
A. The adrenal glands, or suprarenal glands, consist of two regions: an inner adrenal
medulla and an outer adrenal cortex (p. 611; Fig. 16.14).
B. The adrenal cortex produces corticosteroids from three distinct regions: the zona glome-
rulosa produces minerocorticoids, the zona fasciculate produces glucocorticoids, and the
zona reticularis produces sex steroids (pp. 612–615; Figs. 16.14–16.15; Table 16.3).
2. Glucocorticoids are released in response to stress through the action of ACTH and
primarily cause gluconeogenesis, as well as use of fats and amino acid by body cells.
3. Gonadocorticoids are mostly weak androgens, which are converted to testosterone and
estrogens in the tissue cells.
VII. The Pineal Gland (pp. 617–618)
A. The only major secretory product of the pineal gland is melatonin, a hormone derived
from serotonin, in a diurnal cycle (p. 617).
VIII. Other Endocrine Glands and Tissues (pp. 618–623; Figs. 16.18–16.19;
Tables 16.4–16.5)
A. The pancreas is a mixed gland that contains both endocrine and exocrine gland cells
(pp. 618–620; Figs. 16.18–16.19).
3. Insulin lowers blood glucose levels by enhancing membrane transport of glucose into
body cells and inhibits glucose production through glycogen breakdown or conversion
of amino acids or fats to glucose (pp. 618–620, Fig. 16.19, Table 16.4).
B. The Gonads and Placenta (pp. 620–621)
1. The ovaries produce estrogens and progesterone.
C. Hormone Secretion by Other Organs (pp. 621–623; Table 16.5)
1. Adipose tissue produces leptin, which acts on the CNS to produce a feeling of satiety;
also resistin, an insulin antagonist, and adiponectin, which increases sensitivity to
insulin.
2. The gastrointestinal tract contains enteroendocrine cells throughout the mucosa that
secrete hormones to regulate digestive functions.
IX. Developmental Aspects of the Endocrine System (pp. 623–624)
A. Endocrine glands derived from mesoderm produce steroid hormones; those derived from
ectoderm or endoderm produce amines, peptides, or protein hormones (p. 623).
C. Old age may bring about changes in rate of hormone secretion, breakdown, excretion,
and target cell sensitivity (pp. 623–624).
1. The amount of connective tissue in the anterior pituitary increases, vascularization
decreases, and the number of hormone-secreting cells declines.
Cross References
Additional information on topics covered in Chapter 16 can be found in the chapters listed below.
1. Chapter 1: Negative feedback
2. Chapter 2: Steroids; amino acids
3. Chapter 3: General cellular function
8. Chapter 14: Norepinephrine and epinephrine
9. Chapter 19: Hepatic portal system; blood pressure control; atrial natriuretic peptide and
blood pressure regulation
10. Chapter 21: Effect of thymic hormones
11. Chapter 23: Gastrin and secretin (hormones of the digestive system)
14. Chapter 26: Antidiuretic hormone function; aldosterone effects on renal tissue;
renin-angiotensin-aldosterone mechanism of blood pressure regulation; role of parathy-
roid hormone and calcium balance related to development; role of atrial natriuretic
peptide and fluid-electrolyte balance; estrogen and glucocorticoid function in fluid and
electrolyte balance
Lecture Hints
1. A flowchart structure is an ideal method to condense a large volume of complex material
into a compact package. Suggest to the class that on a single, large sheet of butcher
2. Emphasize that minute quantities of hormone are all that is necessary to have rather large
effects in the body.
3. Students are often confused regarding the actual site of neurohypophyseal hormone
4. Point out the importance of receptor regulation in non-insulin-dependent (type 2) diabetes.
5. The mechanism of hormone action is an ideal way to introduce some critical thought
questions for the class. Ask the class: “Knowing the properties of steroids and proteins,
how should these hormones be carried in the blood, and which mechanism (second
messenger or intracellular receptor) demands what class of hormone?”
Activities/Demonstrations
1. Audiovisual materials are listed in the Multimedia in the Classroom and Lab section of
this Instructor Guide (p. 387).
Critical Thinking/Discussion Topics
1. Discuss how the negative feedback mechanism controls hormonal activity and yet allows
hypo- and hypersecretion disorders to occur.
3. Discuss the role of the endocrine system in stress and stress responses.
4. Explain the basis of the fact that nervous control is rapid but of short-duration, whereas
hormonal control takes time to start but the effects last a long time. How would body
function change if the rate of hormone degradation increased? Decreased?
as complete as possible.
Library Research Topics
1. Research the role of hormones in treatment of non-hormone-related disorders.
2. Study the inheritance aspect of certain hormones (such as diabetes mellitus, and certain
thyroid gland disorders).
List of Figures and Tables
All of the figures in the main text are available in JPEG format, PPT, and labeled & unlabeled
format on the Instructor Resource DVD. All of the figures and tables will also be available in
Transparency Acetate format. For more information, go to www.pearsonhighered.com/educator.
Figure 16.1 Location of selected endocrine organs of the body.
Figure 16.2 Cyclic AMP second-messenger mechanism of water-soluble
hormones.
Figure 16.7 Disorders of pituitary growth hormone.
Figure 16.8 Regulation of thyroid hormone secretion.
Figure 16.9 The thyroid gland.
Figure 16.10 Synthesis of thyroid hormone.
Figure 16.11 Thyroid disorders.
Figure 16.12 The parathyroid glands.
Figure 16.13 Effects of parathyroid hormone on bone, the kidneys,
Table 16.1 Pituitary Hormones: Summary of Regulation and Effects
Table 16.2 Major Effects of Thyroid Hormone (T4 and T3) in the Body
Answers to End-of-Chapter Questions
Multiple-Choice and Matching Question answers appear in Appendix H of the main text.
Short Answer Essay Questions
15. A hormone is a chemical messenger that is released into the blood to be transported
throughout the body. (p. 593)
16. Binding of a hormone to intracellular receptors would result in the most long-lived
response. Membrane-bound receptors activate second-messengers that are degraded
17. a. The anterior pituitary is connected to the hypothalamus by a stalk of tissue, the
infundibulum (p. 598); the pineal gland is suspended from the roof of the third
ventricle (p. 617); the pancreas is located dorsal to the stomach, and is partially retrop-
eritoneal (p. 618); the ovaries are retroperitoneal organs within the female pelvic
18. Endocrine glands/regions that are important in stress response are the adrenal medulla
and adrenal cortex. The adrenal medulla produces hormones epinephrine and norepine-
19. The release of anterior pituitary hormones is controlled by hypothalamic-releasing (and
hypothalamic-inhibiting) hormones. (p. 602)
20. The posterior pituitary is neural tissue, not glandular. It is composed largely of the axon
21. A lack of iodine (required to make functional T3 and T4) causes a colloidal, or endemic,
goiter. (p. 608)
22. With the insulin deficiency characteristic of type I diabetes mellitus, the balance between
insulin and glucagon is upset. Glucagon becomes the major hormone controlling blood
23. Specialized cardiac muscle cells produce atrial natriuretic peptide, which promotes sodium
and water loss in the kidneys. (p. 614) Neurons of the posterior pituitary secrete oxytocin,
24. Stress may drive up cortisol secretion, contributing to memory loss or loss of cognitive
function. Lower levels of aldosterone may cause plasma K+ to be somewhat elevated.
Critical Thinking and Clinical Application Questions
2. Insulin should be administered because symptoms are indicative of diabetic shock. (p. 620)
3. The hypersecreted hormone is growth hormone, which will result in gigantism, if it is not
4. a. A likely possibility is that Sean has Addison’s disease, which is a hyposecretory
disorder of the adrenal cortex affecting secretion of both glucocorticoids and minero-
corticoids. The primary minerocorticoid, aldosterone, is responsible for promoting Na+
5. Mr. Proulx is suffering from Cushing’s syndrome, brought on by his prednisone. His
overall lousy feeling is due to muscle weakness and possible hyperglycemia, the swelling
is due to water and salt retention, and the anti-inflammatory effect of the drug plays a
Suggested Readings
Aggarwal, P. and A. Zavras. “Parathyroid Hormone and its Effects on Dental Tissues.” Oral
Diseases 18 (1) (Jan. 2012): 48–54.
Birnbaum, Morris J. “Dialogue Between Muscle and Fat.” Nature 409 (6821) (Feb. 2001):
672–673.
(Dec. 2001): 792–799.
Pittman, D. “A Neuro-Endocrine-Immune Symphony.” Journal of Neuroendocrinology 23
(12) (Dec. 2011): 1296–1297.
Rabinovitch, Alex. “Autoimmune Diabetes Mellitus.” Science and Medicine 7 (3) (May/
June 2002): 18–27.
Raloff, Janet. “Can Childhood Diets Lead to Diabetes?” Science News 159 (7) (Feb. 2001):
111.
