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U N I T 9
Endocrine System
Treatment of hypopituitarism includes treating
any identified underlying cause. Hormone deficiencies
require replacement therapy with appropriate hormones.
Cortisol replacement is started when ACTH deficiency
is present, thyroid replacement when TSH deficiency is
detected, and sex hormone replacement when LH and
FSH are deficient. Growth hormone replacement is indi-
cated for pediatric GH deficiency and is being increas-
ingly used to treat GH deficiency in adults.
2,7,8
Growth and Growth Hormone
Disorders
Several hormones are essential for normal body growth
and maturation, including growth hormone, insulin,
thyroid hormone, and androgens.
9
Insulin, for example,
plays an essential role in growth processes, in addi-
tion to its actions on carbohydrate and fat metabolism.
Children with diabetes, particularly those with poor
control, often fail to grow normally even though GH
levels are normal. When levels of thyroid hormone are
lower than normal, bone growth and epiphyseal closure
are delayed. Androgens such as testosterone and dihy-
drotestosterone exert anabolic growth effects through
their actions on protein synthesis. Glucocorticoids at
excessive levels inhibit growth, apparently because of
their antagonistic effect on GH secretion.
Growth Hormone
Growth hormone, also called
somatotropin
, is a
191-amino-acid polypeptide hormone synthesized and
secreted by special cells in the anterior pituitary called
somatotropes.
2
For many years, it was thought that
GH was produced primarily during periods of growth.
However, this has proved to be incorrect because the
rate of GH production in adults is almost as great as in
children.
Growth hormone is necessary for growth and contrib-
utes to the regulation of metabolic functions (Fig. 32-1). All
aspects of cartilage growth are stimulated by GH; one of
the most striking effects of GH is on linear bone growth,
resulting from its action on the epiphyseal growth plates
of long bones. The width of bone also increases because
of enhanced periosteal growth. Visceral and endocrine
organs, skeletal and cardiac muscle, skin, and connec-
tive tissue all undergo increased growth in response to
GH. In many instances, the increased growth of visceral
and endocrine organs is accompanied by enhanced func-
tional capacity. For example, increased growth of cardiac
muscle is accompanied by an increase in cardiac output.
Increased
linear
growth
Increased
size and
function
Increased
lean muscle
mass
Anterior
pituitary
Growth hormone
Growth-promoting actions
Liver
Anti-insulin effects
Increased protein synthesis
Bone and
cartilage
Body
organs
Muscle
Adipose
tissue
Carbohydrate
metabolism
Decreased
glucose use
Increased blood
glucose
Increased lipolysis
Increased FFA use
Decrease in
adiposity
IGF-1
Hypothalamus
FIGURE 32-1.
Growth-promoting and anti-insulin effects of growth hormone. FFA, free fatty acids;
IGF-1, insulin-like growth factor-1.
