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 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 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.