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 parathyroid 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
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 active 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 parathormone 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.