b. The pituitary gland is frequently referred to as the "leader of the endocrine
orchestra" because of its widespread effect upon the other glands in the body, either
modifying or controlling their secretions. The anterior lobe plays the master role and
many different effects have been attributed to it.
(1) Somatotropin (growth hormone) (GH or STH). Somatotropin causes
growth of all tissues of the body that are capable of growing. This hormone causes both
increased size of the cell itself and increased mitosis with the development of increased
numbers of cells. This hormone increases the rate of protein synthesis in all the cells of
the body, decreases the rate of carbohydrate utilization, and increases the mobilization
of fats and use of fats for energy.
(2) Corticotropin (adrenocorticotropin, ACTH). Corticotropin stimulates the
adrenal cortex. ACTH causes the adrenal cortex to produce an increased quantity of
hormones. It also controls the adrenal cortex to the extent that if the pituitary gland is
removed, the adrenal cortex atrophies and becomes degenerate. If fresh pituitary gland
is introduced, the adrenal cortex repairs itself.
(3)
Thyrotropin (TSH).
(a) Stimulates thyroxine activity. Thyrotropin increases the rate at
which the thyroid cells take up inorganic iodine from the blood. Thyrotropin further
increases the rate at which thyroxine in the thyroid is released into the blood.
(b) Stimulates thyroid growth. Thyrotropin causes an increase in the
size of the thyroid cells and also an increase in the number of cells.
(4)
Follicle-stimulating hormone (FSH).
(a) Graafian follicle control. In the female, FSH causes the proliferation
of the ovarian follicular cells during growth of the Graafian follicles.
These cells are also stimulated to secrete small amounts of estrogen.
(b) Induction of spermatogenesis. In the male, FSH stimulates
spermatogenesis.
(5) Luteinizing hormone (LH) (interstitialcell-stimulating hormone, ICSH). In
the female, LH joins with the follicle-stimulating hormone to stimulate estrogen
secretion. LH also promotes the rupture of the follicle to release the ovum so that it may
be impregnated. In the male, it stimulates the production of testosterone.
(6) Luteotropic hormone (LTH, prolactin). In females, LTH promotes the
growth of breast tissue and lactation. In concert with the luteinizing hormone, it
stimulates and maintains the corpus luteum, which secretes progesterone and
estrogens.
MD0956
3-49
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