THE ENDOCRINE SYSTEM
The endocrine glands differ markedly in
appearance and are widely separated in the body. The pituitary is a round mass
about the size of a large green pea, attached by a stalk to the brain stem. The
thyroid, deep in the throat, has been likened to a small oyster, though it is
beefy red in color. Attached to the thyroid are the parathyroid-generally four,
although there may be more or less-which somewhat resemble BB shots.
The
adrenals, rising like mushrooms from atop the kidneys, are two in number. Each
consists of a core, the medulla, and a casing, the cortex. The pancreas, lying
against the back wall of the abdomen, might appear at first glance to be no
endocrine gland at all, since it has a duct leading into the intestine. But in
the tail and elsewhere it also has a few tiny segments, called islets, which
form an endocrine gland, pouring their secretions into the bloodstream. The
gonads, or sex glands, consist of testes in men and ovaries in women. In
addition, there are the pineal gland in the upper back part of the brain, and
the thymus which is found below the thyroid in young people. and withers away.
The hormones these
glands send through the blood to various parts of the body act like messengers
(the word hormone comes from the Greek word meaning to excite or stir up). The
hormones do not actually create processes; instead they give the orders for
certain processes to speed up or slow down. And the endocrine glands form an
interdependent system. In a sense, they can be likened to a family in that what
happens to one affects the others.
If one gland is removed, the functioning of
all others is altered. Similarly, if the functioning of one increase so its
secretions increase, others are affected. This is one reason why it can be
dangerous to dose oneself with a hormone, glandular tissue or extract, or
whatever it may be called, (or the purpose of reducing weight, getting rid of
.'X oo ",,, hair, developing the breasts,
becoming more virile, or for any other reason.
As an example of how the glands
work together, the pituitary secretes a hormone that moves through the blood to
the adrenals to stimulate the latter. In turn, the adrenals secrete a hormone
that travels to the pituitary and signals the latter to slow production of the
adrenal-arousing hormone. Actually, the pituitary secretes hormones to stir up
each of the other endocrine glands, and each gland responds in the same way.
Until recently, it was thought that the pituitary was the "master"
gland. But it is now evident that the pituitary is no all-powerful monarch on
its own. It is connected to the floor of one of the ventricles in the brain
called the hypothalamus.
