The pituitary gland
The pituitary gland, which is also called the hypophysis, is attached to the hypothalamus at the base of the brain (Figure 3.1). Secretion of the hormones of the pituitary gland is regulated by the hypothalamus and it is through the hypothalamic-pituitary connection that external and internal stimuli can influence the release of the pituitary hormones, thus producing the neural-endocrine interaction. The pituitary has been called the body's “master gland” because its hormonal secretions stimulate a variety of endocrine glands to synthesize and secrete their own hormones. However, it is really the hypothalamus that is the master gland, because it controls the pituitary.
The pituitary gland consists of two primary organs: the anterior pituitary (adenohypophysis or pars distalis) which is a true endocrine gland, and the posterior pituitary (neurohypophysis) which is formed from neural tissue and is an extension of the hypothalamus (Figure 3.1). The pituitary gland is attached to the hypothalamus by the pituitary (hypophyseal) stalk. Further details of the anatomy and physiology of the pituitary gland can be found elsewhere (Norman and Litwack 1997; Amar and Weiss 2003; Boron and Boulpaep 2005; Gardner and Shoback 2011).
The neurohypophysis (posterior pituitary)
The neurohypophysis consists of neural tissue and contains the nerve terminals (about 100,000) of axons whose cell bodies are located in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus. The axons of these large magnocellular neurosecretory cells project down from the hypothalamus through the part of the pituitary stalk called the infundibulum and terminate in the posterior pituitary gland (Figure 3.2). The neurosecretory cells of the PVN and SON manufacture the hormones oxytocin and vasopressin (also called antidiuretic hormone, ADH), which are transported down the axons and stored in nerve terminals in the posterior pituitary. The axon terminals in the posterior pituitary are surrounded by supporting cells called pituicytes.