what is feedback mechanism? how it controls the seceretion of hormone?

Feedback mechanism is the process which helps to maintain the normal state of body by controlling the hormonal secretions.

There are two kinds of feedback mechanisms:

1. Negative Feedback Mechanism:

Whenever there is a change in the normal state, the messages are sent to ‘increase’ secretions if there is a fall below normal or to ‘decrease’ secretions if there is a rise above normal to restore the normal body state. Such a mechanism is called a Negative Feedback Mechanism.
Example: Blood sugar level

The increase in blood sugar level stimulates the secretion of insulin so that the sugar level is maintained. If the blood sugar level falls below normal,   then it stimulates the secretion of glucagon. Glucagon stimulates the  breakdown of glycogen to glucose, and thus, the normal sugar level is maintained.

2. Positive Feedback Mehcanism:

This type of mechanism is very rare.
Example: Uterine contractions during child birth. In the normal state, the uterine muscles are relaxed. One contraction of muscles stimulates the secretion of oxytocin which further increases the contraction of uterine muscles.