Pituitary gland: The main endocrine gland. It is a small structure in the head. It is called the master gland because it produces hormones that control other glands and many body functions including growth.The pituitary consists of the anterior and posterior pituitary.The anterior pituitary is the front portion of the pituitary.t is called the master gland because it produces hormones that control other glands and many body functions including growth. The pituitary consists of the anterior and posterior pituitary. The anterior pituitary is the front portion of the pituitary.