Zoology 10th Edition by Stephen Miller,John Harley

Exercise 15

The three major chemical classes of endocrine hormones are peptides and proteins, amino acids and amino acid derivatives, and steroids. Feedback control is necessary to maintain homeostasis in an animal's body. The anterior pituitary and hypothalamus are themselves partially controlled by the very hormones whose secretion they stimulate. In most cases, this control is inhibitory (negative feedback) in order to maintain relatively constant levels of the target hormone.
Why are hormones not continuously secreted?