Chapter 16
The Endocrine System
603
16
HORMONE (CHEMICAL
STRUCTURE AND CELL TYPE)
REGULATION OF RELEASE
TARGET ORGAN AND EFFECTS
EFFECTS OF HYPOSECRETION
g
AND HYPERSECRETION
h
Thyroid-stimulating hormone
(TSH)
(Glycoprotein, thyrotropic
cells)
Stimulated
by TRH* and in infants
indirectly by cold temperature
Inhibited
by feedback inhibition
exerted by thyroid hormones
on anterior pituitary and
hypothalamus and by GHIH*
Thyroid gland: stimulates thyroid
gland to release thyroid hormones
g
Cretinism in children;
myxedema in adults
h
Hyperthyroidism; effects
similar to those of Graves'
disease, in which antibodies
mimic TSH
Adrenocorticotropic hormone
(ACTH)
(Peptide, corticotropic
cells)
Stimulated
by CRH*; stimuli that
increase CRH release include fever,
hypoglycemia, and other stressors
Inhibited
by feedback inhibition
exerted by glucocorticoids
Adrenal cortex: promotes release
of glucocorticoids and androgens
(mineralocorticoids to a lesser
extent)
g
Rare
h
Cushing's disease
Follicle-stimulating hormone
(FSH)
(Glycoprotein,
gonadotropic cells)
Stimulated
by GnRH*
Inhibited
by feedback inhibition
exerted by inhibin, and estrogen in
females and testosterone in males
Ovaries and testes: in females,
stimulates ovarian follicle
maturation and estrogen
production; in males, stimulates
sperm production
g
Failure of sexual
maturation
h
No important effects
Luteinizing hormone (LH)
(Glycoprotein, gonadotropic
cells)
Stimulated
by GnRH*
Inhibited
by feedback inhibition
exerted by estrogen and
progesterone in females and
testosterone in males
Ovaries and testes: in females,
triggers ovulation and stimulates
ovarian production of estrogen and
progesterone; in males, promotes
testosterone production
As for FSH
Prolactin (PRL)
(Protein,
prolactin cells)
Stimulated
by decreased PIH*;
release enhanced by estrogens,
birth control pills, breast-feeding,
and dopamine-blocking drugs
Inhibited
by PIH* (dopamine)
Breast secretory tissue: promotes
lactation
g
Poor milk production in
nursing women
h
Inappropriate milk
production (galactorrhea);
cessation of menses in
females; impotence in males
*Indicates hypothalamic releasing and inhibiting hormones: GHRH
5
growth hormone–releasing hormone; GHIH
5
growth hormone–inhibiting hormone;
TRH
5
thyrotropin-releasing hormone; CRH
5
corticotropin-releasing hormone; GnRH
5
gonadotropin-releasing hormone; PIH
5
prolactin-inhibiting hormone
IGFs stimulate actions required for growth: (1) uptake of nu-
trients from the blood and their incorporation into proteins and
DNA, allowing growth by cell division; and (2) formation of
collagen and deposition of bone matrix. Although GH stimu-
lates most body cells to enlarge and divide, its major targets are
bone and skeletal muscle. Stimulation of the epiphyseal plate
leads to long bone growth, and stimulation of skeletal muscles
increases muscle mass.
Regulation of Secretion
Secretion of GH is regulated chiefly
by two hypothalamic hormones with antagonistic effects.
Growth hormone–releasing hormone (GHRH)
stimulates
Tis
glucose sparing
action, which raises blood glucose levels,
is called the
anti-insulin effect
of GH because its effects oppose
those of insulin. In addition, GH increases amino acid uptake
into cells and their incorporation into proteins.
Indirect Actions on Growth
GH mediates most of its growth-
enhancing effects indirectly via a family of growth-promoting
proteins called
insulin-like growth factors (IGFs)
. Te liver,
skeletal muscle, bone, and other tissues produce IGFs in re-
sponse to GH. IGFs produced by the liver act as hormones,
while IGFs made in other tissues act locally within those tissues
(as paracrines).
Table 16.1
(continued)
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