The secretion of most hormone is controlled by a positive feedback system.

a. True

b. False

False

Explanation:

Regulation of the secretion of various hormones into the bloodstream is done by a mechanism known as negative feedback.

The term feedback is used to indicate the regulation of a gland by its own end product. Feedback is negative because increased end product inhibits gland activity.

An example of negative feedback is the control exerted by the pituitary gland over the thyroid gland. The pituitary produces a trophic hormone, thyrotropin, which stimulates the thyroid to release thyroxine and triiodothyronine hormones. When these hormones reach a certain concentration in the blood, they inhibit the production of thyrotropin by the pituitary gland.

When the rate of thyrotropin in the blood decreases, so do the rates of thyroxine and triiodothyronine in the blood. This undoes the inhibitory effect on the pituitary gland, which increases thyrotropin production and restarts the regulatory cycle.