Anterior Pituitary:
Hypothalamic hormones
released into special blood vessels
(the hypophyseal portal system) control the release of anterior pituitary hormones.
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2
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When appropriately stimulated,
hypothalamic neurons secrete
releasing or inhibiting hormones
into the primary capillary plexus.
Hypothalamic hormones travel
through portal veins to the anterior
pituitary where they stimulate or
inhibit release of hormones made
in the anterior pituitary.
In response to releasing
hormones, the anterior pituitary
secretes hormones into the
secondary capillary plexus. This in
turn empties into the general
circulation.
Hypothalamus
Superior
hypophyseal
artery
Hypothalamic
neurons synthesize
GHRH, GHIH, TRH,
CRH, GnRH, PIH.
Hypophyseal
portal system
Anterior lobe
of pituitary
GH, TSH, ACTH,
FSH, LH, PRL
Primary capillary
plexus
Hypophyseal
portal veins
Secondary
capillary plexus
A portal system
is two capillary
plexuses (beds)
connected by
veins.
Anterior lobe
of pituitary
unconscious or comatose patients, so accident victims with
head trauma must be carefully monitored.
Te opposite problem, hypersecretion of ADH, can occur
in children with meningitis, or in adults who have neurosur-
gery, hypothalamic injury, or cancer (particularly lung cancer)
in which cancer cells are additional sources of ADH. It also
may occur aFer general anesthesia or administration of certain
drugs. Te resulting condition,
syndrome of inappropriate ADH
secretion
(
SIADH
), is marked by retention of fluid, headache
and disorientation due to brain edema, weight gain, and de-
creased solute concentration in the blood. SIADH management
requires restricting fluids and carefully monitoring blood so-
dium levels.
Anterior Pituitary Hormones
Te anterior pituitary has traditionally been called the “mas-
ter endocrine gland” because many of the numerous hormones
it produces regulate the activity of other endocrine glands. In
recent years, however, it has been dethroned by the hypothala-
mus, which is now known to control the activity of the anterior
pituitary.
Researchers have identified six anterior pituitary hormones,
all of them proteins—growth hormone, thyroid-stimulating
hormone, adrenocorticotropic hormone, follicle-stimulating
hormone, luteinizing hormone, and prolactin (±able 16.1).
When the anterior pituitary receives an appropriate chemical
stimulus from the hypothalamus, it releases one or more of its
hormones. Although many different hormones pass from the
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