Homeostatic Imbalance
16.1
One result of ADH deficiency is
diabetes insipidus
, a syndrome
marked by intense thirst and huge urine output. Te name of
this condition (
diabetes
5
overflow;
insipidus
5
tasteless) dis-
tinguishes it from diabetes mellitus (
mel
5
honey), in which
insulin deficiency causes large amounts of blood glucose to be
lost in the urine. At one time, a clinician would taste the patient’s
urine to determine the type of diabetes.
Diabetes insipidus can be caused by a blow to the head that
damages the hypothalamus or the posterior pituitary. Tough
inconvenient, the condition is not serious when the thirst center
is operating properly and the person drinks enough water to
prevent dehydration. However, it can be life threatening in
Drinking alcoholic beverages inhibits ADH secretion and
causes copious urine output. Te dry mouth and intense thirst
of a “hangover” reflect this dehydrating effect. As you might
expect, drinking lots of water also inhibits ADH release.
Diuretic drugs
antagonize the effects of ADH and flush water
from the body. Diuretics are used to manage some cases of hy-
pertension and the edema (water retention in tissues) typical of
congestive heart failure.
Under certain conditions, such as severe blood loss, excep-
tionally large amounts of ADH are released. At such high blood
concentrations, ADH causes vasoconstriction, primarily of vis-
ceral blood vessels, raising blood pressure. Tis response targets
different ADH receptors found on vascular smooth muscle. For
this reason, ADH is also called
vasopressin
.
Figure 16.5
The hypothalamus controls release of hormones
from the pituitary gland in two different ways.
Posterior Pituitary:
Action potentials
travel down the axons of hypothalamic neurons,
causing hormone release from their axon terminals in the posterior pituitary.
1
2
3
4
Hypothalamic neurons synthesize
oxytocin or antidiuretic hormone
(ADH).
Oxytocin and ADH are
transported down the axons of the
hypothalamic- hypophyseal tract
to the posterior pituitary.
Oxytocin and ADH are stored in
axon terminals in the posterior
pituitary.
When associated hypothalamic
neurons fire, action potentials
arriving at the axon terminals cause
oxytocin or ADH to be released into
the blood.
Paraventricular nucleus
Supraoptic
nucleus
Optic chiasma
Hypothalamus
Inferior
hypophyseal
artery
Oxytocin
ADH
Infundibulum
(connecting stalk)
Hypothalamic-
hypophyseal
tract
Axon terminals
Posterior lobe
of pituitary
Posterior lobe
of pituitary
FOCUS
Hypothalamus and Pituitary Interactions
 
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