Control of Endocrine Glands
Each hormone released by the endocrine glands has its own mechanism that controls the level in plasma. Most endocrine gland secretions are controlled by a negative feedback mechanism (see Figure 6.2A).For example, the secretion of hormones by the en-docrine gland is triggered by a stimulus. The hor- mone secreted reduces the activity of the stimulus and this, in turn, reduces the secretion of the hor-mone. This type of control is similar to the reflexes in the nervous system. Sometimes, like a polysynaptic reflex, there are many steps involved in the control of endocrine secretion.
Rarely, secretions are controlled by a positive feed-back mechanism (see Figure 6.2B) in which the hor-mone secreted increases the activity of the stimulus.