497
CHAPTER THIRTEEN
Endocrine System
I
nsufficient secretion of human growth hor-
mone (HGH) during childhood produces
hypopituitary dwarf
sm.
Body proportions and
mental development are normal, but because
secretion of other anterior pituitary hormones
is also below normal, additional hormone defi-
ciency symptoms may appear. For example, a
child with this condition often fails to develop
adult sexual features unless he or she receives
hormone therapy.
HGH can treat hypopituitary dwarfism if
administration begins before the bones com-
pletely ossify. It is also used to treat various condi-
tions that include very short stature but in which
HGH is not de±
cient. These include chronic renal
failure, Turner syndrome, intrauterine growth
retardation, and Prader-Willi syndrome, as well as
some cases of extreme short stature for which no
cause is known. HGH may also delay muscle wast-
ing in people who have AIDS.
The reputation of HGH as an antiaging
agent stems from a 1990 study in which a dozen
men over age sixty who received the hormone
showed slight improvements in muscle mass and
bone mineral density. The media interpreted
this tiny study to indicate that HGH reverses
aging, fueling the many websites that attempt
to sell the hormone, in various guises, as a treat-
ment against the ravages of time. A more recent
meta-analysis—a study of studies—a²
rmed that
HGH in older individuals can both increase mus-
cle mass and decrease fat. It did not, however,
improve strength, so may have merely replaced
some fat with water. Adverse effects that can
occur with excess HGH include joint pain and
swelling and increased diabetes mellitus risk.
Oversecretion of growth hormone in child-
hood may result in
gigantism,
in which height
may eventually exceed 8 feet. Gigantism is usu-
ally caused by a tumor of the pituitary gland,
which secretes excess pituitary hormones includ-
ing GH. As a result, a person with gigantism may
have other metabolic disturbances.
If growth hormone is oversecreted in an
adult after the epiphyses of the long bones have
ossi±
ed, the person does not grow taller. The soft
tissues, however, continue to enlarge and the
bones thicken, producing a large tongue, nose,
hands and feet, and a protruding jaw. This condi-
tion, acromegaly, is also associated with a pitu-
itary tumor (±
g. 13A).
13.2
CLINICAL APPLICATION
Growth Hormone Ups and Downs
from the ovaries. Other functions of the gonadotropins and
their interactions are discussed in chapter 22.
The mechanism that regulates secretion of gonadotro-
pins is not well understood. However, starting at puberty,
the hypothalamus secretes a
gonadotropin-releasing hor-
mone
(GnRH). Gonadotropins are absent in the body fl
uids
of infants and children.
PRACTICE
18
What is the function of ACTH?
19
Describe the functions of FSH and LH in a male and in a female.
20
What is a gonadotropin?
adrenal cortical hormones. Stress can increase secretion of
ACTH by stimulating release of CRH.
Both
follicle-stimulating hormone
and
luteinizing
(lu
te
in-ı¯z
ing)
hormone
are glycoproteins and are called
gonadotropins,
which means they act on the gonads or repro-
ductive organs. FSH controls growth and development of fol-
licles that house egg cells in the ovaries. It also stimulates
the follicular cells to secrete a group of female sex hormones,
collectively called
estrogen
(or estrogens).
In males, FSH stimulates the production of sperm cells
in the testes. LH promotes secretion of sex hormones in both
males and females and is essential for release of egg cells
(a)
(b)
(c)
(d)
FIGURE 13A
Natural oversecretion of growth hormone in adulthood causes acromegaly. Note the changes in this woman’s facial features at
ages (
a
) nine, (
b
) sixteen, (
c
) thirty-three, and (
d
) ±
fty-two. Abuse of growth hormone (as a drug) can cause acromegaly.
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