Why pituitary gland is called as master gland?

(a) The pituitary is called “Master Endocrine Gland” because of number of hormones it produces and the control it exercises over other endocrine gland.
(b) It itself is under the control of the releasing- hormones secreted by the hypothalamus of the brain. Thus, there is a chain of orders : the hypothalamus directs the pituitary output, which controls the secretion of hormones by other endocrine glands