Other hypothalamic neurosecretory cells make and
secrete
antidiuretic hormone (ADH)
through the poste-
rior pituitary (Figure 9.6). These cells sense increases
in the salt concentration in the blood (osmolarity) and
release ADH. ADH acts on the kidneys, sweat glands, ar-
terioles, and brain to conserve body water and increase
blood pressure.
The most common pituitary disorder is diabetes
insipidus, which is caused by a lack of ADH secretion.
Diabetes insipidus is most often caused by brain tumors,
head trauma, or damage to the
pituitary
gland,
pituitary stalk,
or hypothalamus during surgery.
Diabetes insipidus
leads
to
ex-
cessive thirst, frequent urination,
and large volumes of urine. While
a normal person can tolerate dehy-
dration for several days, individu-
als with diabetes insipidus cannot
tolerate dehydration for even a day.
antidiuretic
hormone (ADH)
A hormone secreted
through the posterior
pituitary lobe that
conserves body water
and increases blood
pressure.
E ffect o f ADH secre tio n s on b o d y
w a te r and b lo o d p ressu re levels • Figure 9.6
PLANNEF
The hypothalamus senses changes in osmolarity and directs neurosecretory
cells to secrete ADH through the posterior pituitary.
Dehydration causes high blood osmolarity,
which is sensed by hypothalamic
osmoreceptors.
Water retention reduces blood osmolarity
and inhibits hypothalamic osmoreceptors.
Osmoreceptors
3
Osmoreceptors stimulate
neurosecretory cells that make
and release ADH.
Reduced osmoreceptor activity reduces or stops
secretion of ADH by hypothalamic
neurosecretory cells.
Hypothalamus
Target tissues
Nerve impulses of the neurosecretory
cells release ADH from terminals in the
posterior pituitary into the bloodstream.
ADH acts on these target tissues:
• Kidneys to retain water
• Sweat glands to reduce water loss
• Arterioles to constrict and increase blood pressure
• Brain to stimulate drinking
These actions restore normal osmolarity and blood pressure.
Endocrine Glands Regulate Key Body Functions
261
PROCESS DIAGRAM
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