Neurohypophysis

Excerpt

The neurohypophysis (pars posterior) is a structure that is located at the base of the brain and is the posterior lobe of the pituitary gland. Its embryological origin is from the neuroectodermal layer called the infundibulum. The neurohypophysis is divided into two regions; the pars nervosa and the infundibular stalk. Sometimes the pars intermedia and the median eminence are included. It secretes oxytocin and vasopressin; vasopressin is also called antidiuretic hormone (ADH) due to its function of preventing diuresis. These hormones are produced at the magnocellular neurosecretory cells in the hypothalamus, specifically, from the paraventricular nuclei and supraoptic nuclei of the hypothalamus. These cells are neurons that project axons to the neurohypophysis. The hormones are transported from the hypothalamus to the neurohypophysis where they are stored and later released into the neurohypophyseal capillaries, which then carry the hormones into the systemic circulation.

Dysfunction of the posterior pituitary affects the hormonal homeostasis, which causes diabetes insipidus (DI), and the syndrome of inappropriate antidiuretic hormone (SIADH) secretion. Disorders caused by oxytocin deficiency are rare, but most are related to pregnancy and lactation problems.

The posterior pituitary contains pituicytes that function in the pars nervosa like glial cells for support and modulation of the release of the hormones. A tumor formed from the pituicytes is called pituicytoma.