Page 89 - The Miracle of Hormones

The Sensitive Calcium-Meters

A Control Mechanism

In earlier pages we have seen that a large part of the functioning of
the hormonal system is under the control of the pituitary gland, but it
will be noticed that the system in place to regulate the amount of calcium
operates under the direction of a different control mechanism. The para-
thyroid glands measure the amount of calcium in the blood and decide
what action to take. If the amount of calcium in the blood is too low, they
secrete parathormone.
If the amount of calcium in the blood is more than is required, the
secretion of parathormone is reduced. This time a different hormone
comes into play: the thyroid gland secretes a hormone called "calcitonin,"
which has the reverse effect of parathormone. That is, it prevents bone
cells from releasing calcium and makes them store it.
The cells which make up the parathyroid gland know that they
must go into action when the amount of calcium decreases, while the
cells which compose the thyroid gland know that they must become ac-
tive when the level of calcium increases. Who put this plan into the cells?
If the parathyroid went into action at the wrong time, when the
amount of calcium was already too high, and parathormone began to be
secreted, a serious danger for human health would result. Or, if parathor-
mone and calcitonin were secreted at the same time, the body cells would
not know what to do. If the cells that make up these glands were slow to
go into action when the need arose (or did not notice that they were
needed) a serious danger to health would again result. The harmonious
functioning of the thyroid and parathyroid glands and the intelligence
guiding the activities of the cells that make up these glands, are all proof
that the human body was created.

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