InSight
E n d o c r in e f u n c tio n s in
n o n - e n d o c r i n e g la n d s
Figure 9.19
There are many cells in various
non-endocrine organs that
secrete hormones.
Thymus
- Releases
thymosin,
which helps
T-cell lymphocytes to mature and slowthe
aging process.
Heart
- When blood volume increases, endocrine
cells in the heart secrete
atrial natruretic peptide,
which stimulates sodium excretion by the kidney,
reducing blood volume and pressure.
Stomach
- Stretching and food in the stomach
causes it to release
gastrin,
which stimulates gastric
glands to secrete gastricjuice and stomach muscles
to increase motility.
Small intestine
secretes several hormones:
•The duodenum secretes
glucose-dependent insulinotropic hormone(GIP),
which stimulates the beta
cells of the pancreas to secrete insulin. GIP coordinates the timing of intestinal glucose absorption with the
insulin-evoked glucose uptake, so that the rise in blood glucose during the digestion of a meal is minimized.
•The mucosa secretes
secretin,
which stimulates the secretion of bicarbonate-rich pancreatic juices.
•The mucosa also secretes
cholecystokinin (CKK),
which stimulates secretion of pancreaticjuices and
ejection of bile from the gallbladder, and inhibits gastric emptying.
The Pineal Gland Sets Daily Cycles
The pineal gland (
PlN-e-al
) is attached to the roof of the
third ventricle in the midline of the brain. The pineal gland
consists of masses of neuroglia and secretory cells called pine-
alocytes (
pin-e-AL-o-sitz
). This gland secretes the hormone
melatonin, which is derived from the amino acid serotonin.
Melatonin is thought to be involved in setting the body’s daily
clock. The pineal gland receives input from the eyes, indicat-
ing that light and dark may influence its activities. In support
of this hypothesis, melatonin secretion is greatest during
sleep and in darkness (almost 10 times greater than at other
times). For patients who have trouble falling asleep, small
doses of melatonin may be taken orally to promote sleep.
Overproduction of melatonin may be the cause of a
type of depression called seasonal affective disorder
(SAD) . SAD afflicts some people during the winter months,
when day length is short. To provide relief from this dis-
order, full-spectrum bright-light therapy (that is, repeated
doses of several hours of exposure to artificial light as bright
as sunlight) is used. Another disorder that may be similar
to SAD is jet lag, fatigue suffered by travelers who quickly
cross several time zones. Three to six hours of exposure to
bright light appears to help speed recovery from jet lag.
There are cells in non-endocrine organs that secrete
hormones. See Figure 9.19 to learn about some impor-
tant endocrine functions in these non-endocrine glands.
1.
What
is the role of aldosterone in the renin-
angiotensin-aldosterone system?
2.
How
is ovulation controlled by hormones?
3.
What
is thought to be the function of the pineal
gland?
4.
What
are the functions of hormones secreted
by endocrine cells that are not located in endo-
crine glands?
274 CHAPTER 9
The Endocrine System
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