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9
CHAPTER SUMMARY
The endocrine system is arguably the most elegant and mysterious of all the body systems. Considered
to be the second great homeostatic system of the body (after the faster-acting nervous system), the
endocrine system controls reproduction, growth and development, body defenses, metabolic
processes, and blood chemistry. Through the use of hormones, the endocrine system maintains
balance within the body in a relatively leisurely and profound way. Hormones circulate in the blood
until reaching the target organs upon which they are designed to act, bind with the awaiting cells, and
immediately begin to influence the internal machinery of those cells.
In this chapter, the mechanisms of hormone action are discussed first, differentiating between
the actions of steroidal and nonsteroidal hormones. Next, the negative feedback mechanisms that
control hormone release are presented. Hormonal, humoral, and neural stimuli are all explained
through the use of selected examples. Endocrine glands are then explained as ductless glands that
release their hormones into blood or lymphatic fluid, to be distinguished from exocrine glands, which
release their products directly into ducts on the epithelial surface.
In the final sections of this chapter, the major endocrine organs and their hormones’
main actions and regulatory functions are presented. The hypothalamus, which also plays an important
role in nervous system functioning, is noted for its role in endocrine control based upon its
relationship with the pituitary gland. The complexity of the pituitary, with its six prominent anterior
hormones and two posterior hormones, is then described. The thyroid is presented next for its role in
both metabolism and blood calcium levels, followed by a discussion of the counterbalancing action of
the parathyroid glands in blood calcium regulation. The cortical and medullar hormones of the adrenal
glands are outlined and clarified for their roles in long- and short-term stress-response, and the islet
cells of the pancreas are then discussed, along with the homeostatic imbalance of diabetes
mellitus. The lesser-understood roles of the pineal and thymus hormones precede the section on
the hormones of the ovaries and testes, and finally, the hormones produced by other tissues pocketed
throughout the body, as well as the hormones produced by the placenta, are discussed. The major
developmental aspects of the endocrine system, including its role in menopause, conclude the chapter.
SUGGESTED LECTURE OUTLINE
I.
THE ENDOCRINE SYSTEM AND HORMONE FUNCTION—AN OVERVIEW (pp. 300–
303)
A.
The Chemistry of Hormones (pp. 300–301)
1.
Assists faster-acting nervous system in the homeostatic control of long-term
processes
a.
Growth and development
b.
Metabolism
c.
Reproduction
d.
Body defense
2.
Amino acid-based molecules
a.
Proteins
b.
Peptides
c.
Amines
3.
Steroid-based hormones—directly influence target tissue DNA
a.
Ovaries
b.
Testes
B.
C.
II.
4.
Prostaglandins
Mechanisms of Hormone Action (pp. 301–303)
1.
Non-steroidal amino-acid based hormones act through second messengers
a.
Cyclic AMP
2.
Ability of hormones to bind determined by receptors on target cells
Control of Hormone Release (p. 303)
1.
Negative feedback loops—metabolism regulation
2.
Stimuli for blood-hormone release
a.
Hormonal
b.
Humeral
c.
Neural
THE MAJOR ENDOCRINE ORGANS (pp. 303–320; Table 9.1)
A.
Pituitary Gland (pp. 304–307)
1.
Enclosed by bone at base of brain
2.
Glandular (anterior) and neural (posterior) portions
a.
Hormones of the Anterior Pituitary
i.
Growth Hormone (GH)
ii.
Prolactin (PRL)—breast milk production
iii.
Adrenocorticotropic Hormone (ACTH)—hormone release
by adrenal cortex
iv.
Thyrotropic Hormone (TH)—thyroid release of thyroid
hormone
v.
Gonadotropic Hormones – begin at puberty
 Follicle-Stimulating Hormone (FSH)—follicle
development and estrogen production by female
ovaries, and sperm production by male testes
 Luteinizing Hormone (LH)—female ovulation and
corpus luteum production of progesterone, and
male testosterone production by testes
 Interstitial Cell-Stimulating Hormone (ICSH)
b.
Pituitary-Hypothalamus Relationship
i.
Releasing and inhibiting hormones made by hypothalamus
regulate hormone release by anterior pituitary
c.
Hormones of the Posterior Pituitary
i.
Oxytocin stimulates uterine contraction and milk ejection
in nursing females
ii.
Antidiuretic Hormone (ADH)—kidney tubule cells
reabsorb and conserve body water and increase blood
pressure by vasoconstriction, with hyposecretion leading to
diabetes insipidus
B.
Thyroid Gland (pp. 307–310)
1.
Thyroid hormones T4 and T3 released when TSH blood levels rise to
regulate metabolic rate at which cells oxidize glucose
a.
Goiters—iodine lack
b.
Hyposecretion—cretinism in children and myxedema in adults
c.
Hypersecretion—Graves’ disease
2.
Calcitonin—released in response to high blood calcium to enhance bone
calcium deposition
C.
Parathyroid Glands (pp. 310–311)
1.
Four small glands on posterior thyroid gland
2.
Parathyroid hormone (PTH)—released in response to low blood calcium to
enhance bone calcium liberation into blood
D.
E.
F.
G.
H.
a.
PTH hyposecretion – tetany
b.
PTH hyposecretion—bone wasting and fractures
Adrenal Glands (pp. 311–314)
1.
Hormones of the Adrenal Cortex
a.
Mineralocorticoids such as aldosterone regulate kidney reabsorption
of sodium and potassium ions
b.
Glucocorticoids resist long-term stress by increasing blood glucose
and depressing inflammation
c.
Sex hormones in males are produced in small amounts throughout
life
d.
General hyposecretion by adrenal cortex results in Addison’s
disease,
e.
Hypersecretion results in hyperaldosteronism, Cushing’s disease, or
inappropriate masculinization
2.
Hormones of the Adrenal Medulla
a.
Epinephrine—nervous system stimulation
b.
Norepinephrine
Pancreatic Islets (pp. 314–316)
1.
Insulin
2.
Glucagon
Pineal Gland (p. 316)
Thymus Gland (p. 316)
Gonads (pp. 316–320)
1.
Hormones of the Ovaries
a.
Estrogens
b.
Progesterone
2.
Hormones of the Testes
a.
Androgens
III.
OTHER HORMONE-PRODUCING TISSUES AND ORGANS (p. 320; Table 9.2)
A.
Placenta (p. 320)
1.
Human chorionic gonadotropin (hCG)
IV.
DEVELOPMENTAL ASPECTS OF THE ENDOCRINE SYSTEM (p. 323)
A.
Aging (p. 323)
B.
Menopause (p. 323)