In addition to the major endocrine glands, other organs have some
hormonal activity as part of their function. These include the thymus,
stomach, small intestines, heart, and placenta.
Thymosin, produced by the thymus gland, plays an important role
in the development of the body's immune system.
The lining of the stomach, the gastric mucosa, produces a hormone,
called gastrin, in response to the presence of food in the stomach.
This hormone stimulates the production of hydrochloric acid and
the enzyme pepsin, which are used in the digestion of food.
The mucosa of the small intestine secretes the hormones secretin
and cholecystokinin.
Secreting stimulates the pancreas to produce a bicarbonate-rich
fluid that neutralizes the stomach acid. Cholecystokinin stimulates
contraction of the gallbladder, which releases bile. It also stimulates
the pancreas to secrete digestive enzyme.
The heart also acts as an endocrine organ in addition to its major
role of pumping blood. Special cells in the wall of the upper chambers
of the heart, called atria, produce a hormone called atrial natriiuretic
hormone, or atriopeptin.
The placenta develops in the pregnant female as a source of nourishment
and gas exchange for the developing fetus. It also serves as a temporary
endocrine gland. One of the hormones it secretes is human chorionic
gonadotropin,
which signals the mother's ovaries to secrete hormones to maintain
the uterine lining so that it does not degenerate and slough off
in menstruation.
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