The pituitary gland is often termed the “master gland.” Under the direct control of the hypothalamus, which in turn receives input from various brain centers via neurotransmitters, the pituitary gland modulates the function of most endocrine glands in the body. The pituitary gland is in fact 2 separate glands juxtaposed against each other: the anterior pituitary or adenohypophysis and the posterior pituitary or neurohypophysis. As the names suggest, both originate from different sources during development. The following discussion will focus on the anterior pituitary gland and its regulation by the brain as well as its impact on the function of peripheral endocrine glands.
The term pituitary is a misnomer. It was first used by Galen who named the small outgrowth under the brain αδην (aden), or gland, in his book, written between 161 and 180 A.D., De Usum Partium (On the Usefulness of the Parts). He believed that it regulated the secretion of nasal mucus. Andreas Vesalius in De Humani Corporis Fabrica (On the Fabric of the Human Body) translated the name into the Latin glans and described it as the gland that processes slime or pituita in Latin, later referring to it as the glandula pituitaria from which the English pituitary gland was derived. In the late 18th century, Samuel Thomas von Soemmerming, a German anatomist and physician, used the less popular term hypophysis from the Greek “hypo” (meaning under) and “physis” (meaning growth).
The anterior and posterior parts of the pituitary gland are derived from ectodermal tissue. The posterior pituitary gland forms from a downward extension of neural ectoderm from the diencephalon of the developing brain. This extension eventually forms the body of the posterior pituitary at its tip (pars nervosa), the body of this extension becomes the stalk or infundibulum, and the part closest to the hypothalamus becomes the median eminence (Fig. 514-1).
Embryogenesis of the pituitary gland showing the progressive developmental stages from invagination of oral and neural ectoderms through formation of Rathke’s pouch and finally the fully developed pituitary sitting in the sella with its hypothalamic connection.
The anterior pituitary forms as an upward invagination of the stomodeum, a depression ventral to the embryonic brain that eventually forms the oral cavity. This upward invagination of oral ectoderm is called Rathke’s pouch. As development progresses, Rathke’s pouch constricts at the base and eventually completely separates from the stomodeum forming a spherical cavity, which disappears eventually as it develops into the anterior pituitary. Failure of the cavity to completely disappear leads to a remnant called a Rathke’s cleft cyst, which is not infrequently found upon imaging of the pituitary.
The anterior wall of Rathke’s pouch develops into the pars distalis, forming ...