C ushing's sy n d ro m e •
Figure 9.17
One symptom of Cushing’s syn-
drome, which results from excess
cortisol, is a round, flushed face.
Secretion of too much cortisol
by the adrenal gland causes a con-
dition called Cushing’s syndrome.
Cushing’s syndrome can be caused by
adrenal tumors or by pituitary tumors that
result in oversecretion of ACTH. Cushing’s syndrome can
also result from using high doses of cortisone for treating ar-
thritis. Overstimulation by cortisol causes muscles to break
down and fat to be redistributed. One obvious symptom is
a round, flushed-looking face (Figure 9.17), along with a
humped back and hanging abdomen. Complications include
increased blood pressure, elevated blood glucose, weakness,
brittle bones, and decreased resistance to stress. Depend-
ing on the cause, Cushing’s syndrome can be treated using
drugs that interfere with cortisol synthesis or by surgical re-
moval of the adrenal glands or pituitary gland.
When the adrenal cortex does not secrete enough
cortisol or aldosterone, the result is a rare disease called
Addison’s disease. Addison’s disease can be caused by
antibodies attacking the adrenal tissue or damage to
the pituitary gland due to surgery or trauma that leads
to insufficient ACTH secretion. Due to the loss of corti-
sol and aldosterone, Addison’s disease patients often have
symptoms including low blood sugar, weight loss, nausea/
vomiting, muscle weakness, low blood pressure, dehydra-
tion, and heart problems (for example, arrhythmias, low
cardiac output). Addison’s disease is usually treated with
artificial glucocorticoids and mineralocorticoids.
A drenal a n d ro g e n s influence sexual c h a racter-
istics and b eh avio rs
In both males and females, the
inner zone of the adrenal cortex secretes adrenal andro-
gens. Before puberty, adrenal androgens contribute to
growth of arm hair and pubic hair in males and pre-pubertal
growth spurts in females. Adrenal androgens have little
influence after puberty in males because the testes secrete
far more androgens (testosterone) than the adrenal gland.
Adrenal androgens have greater effects in females after
puberty; they influence sex drive and become converted
to estrogens (female hormones). While a female is fertile
(between puberty and menopause), the ovaries are the
organs primarily responsible for the secretion of estro-
gens. (You will learn more about the ovaries shortly.) After
menopause, the conversion of adrenal androgens into es-
trogens becomes the only source of natural estrogen.
E pinephrine
and
n o rep in ep h rin e
re g u la te
th e
b o d y 's
re sp o n se
to
stre ss and
exercise
The cells of the
adrenal medulla are like post-ganglionic
nerve cells of the autonomic nervous sys-
tem. Upon nervous stimulation, they se-
crete the hormones epinephrine (adrena-
line) and norepinephrine (noradrenaline).
These hormones act on many tissues to ac-
complish the following functions:
Increase heart rate and force of contraction, which
increases blood pressure and blood flow
Constrict blood vessels and raise blood pressure
Increase blood flow to the heart, liver, and skeletal
muscles
Dilate airways of the lung, which increases ventilation
Break down liver glycogen into glucose, which is
released into the blood
Break down adipose tissue fats into fatty acids, which
are released into the blood
These responses help the body during activities such as
exercise by mobilizing energy reserves, bringing more oxy-
gen into the body through the lungs, and increasing oxy-
gen delivery to working muscles.
The Hypothalamus, Pituitary Gland,
and Gonads Regulate Reproduction
The gonads, or sex-cell-producing organs, are the ova-
ries, which are located in the pelvis of the female, and the
testes, which lie in the scrotal sac of the male. The ova-
ries produce the hormones estrogen and progesterone.
These female sex hormones stimulate the development of
female sex characteristics at puberty (for example, female
body shape, pubic hair growth, breast development), reg-
ulate the menstrual cycle, and maintain pregnancy. The
ovaries also produce other hormones, inhibin and relaxin,
that have roles in pregnancy.
The testes produce testosterone, which is responsible
for development of the male sex characteristics at puber-
ty (for example, muscle growth, thickening of the vocal
cords, increased facial and pubic hair) and sperm devel-
opment. The testes also produce inhibin, which inhibits
secretion of FSH from the pituitary gland.
Let’s take a brief look at how the hypothalamus, ante-
rior pituitary, and gonads work together to control the se-
cretions of sex hormones, determine the onset of puberty,
and maintain normal sexual functions (
). We
will return to this topic in greater detail in Chapter 16.
272 CHAPTER 9
The Endocrine System
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