Pituitary Gland Function

Essay 89: Pituitary Gland Function The pituitary gland is a pea sized region of specialized endocrine cells and neurons located behind the optic chiasm and enclosed in a bony structure called the sella turcica, or Turkish saddle. Although the pituitary is often called the “master gland” of the endocrine system, that label is more appropriate for an adjacent area of brain known as the hypothalamus. As 19th century scientists deciphered the anatomy and physiology of the central nervous system and endocrine glands, the role of the pituitary gradually became clear.

Today, biologists separate pituitary function into the anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis). Each will be considered in turn.

The anterior

Instead, axons from two groups of hypothalamic neurons - the supraoptic nucleus (SON) and paraventricular nucleus (PVN) – terminate in the posterior pituitary.

These specialized neurons produce the hormones ADH (antidiuretic hormone), also known as vasopressin, and oxytocin. When a person becomes dehydrated, osmoreceptors in the brain trigger ADH release into the systemic circulation. ADH travels to the kidneys where it promotes water reuptake in the epithelial cells lining the collecting ducts.

The exact mechanism of action of ADH remained obscure until 1990, when Peter Agre discovered a class of protein channels, now called aquaporins, which selectively allow water molecules to cross the cell membrane. ADH activates a G-protein coupled receptor on these epithelial cells, triggering an influx of calcium ions, the activation of Protein Kinase C, and the translocation of aquaporins to the cell surface leading to enhanced water reuptake.

Oxytocin has two main functions. First, it triggers uterine contractions when a pregnant woman goes into labor. Second, it promotes the movement of milk from the breast ducts to the nipple by stimulating the contraction of myoepithelial cells lining the ducts. In lactating women, this is sometimes called the milk-let-down reflex. The function of oxytocin in male physiology remains