Hypothalamic neurohypophyseal system

Clinic

• HNS consists of the supraoptic and paraventricular nuclei (SON and PVN) and their axons that run towards the neurohypophysis.
• Vasopressin and oxytocin are released into the blood circulation from where these neurohormones act on peripheral organs.
• HNS represents the classic example of a neuroendocrine system, i.e. of hormone producing neurons.
• Vasopressin acts as an antidiuretic hormone on the kidney and regulates free water clearance by V2-type vasopressin receptors and the subsequent formation of aquaporin-2 water channels in the renal collecting duct.
• In women, oxytocin is involved in labor and lactation by its actions on the uterus and mammary gland respectively
• Posterior pituitary also contains pituicytes, specialized glial cells resembling astrocytes assisting in the storage and release of the hormones.

Function

Two hormones are classically considered as being related to the posterior pituitary: oxytocin and vasopressin. These hormones are created in the hypothalamus and released in the posterior pituitary. After creation, they are stored in neurosecretory vesicles regrouped into Herring bodies before being secreted in the posterior pituitary via the bloodstream.

Hormone	Other names	Main targets	Effect	Clinical significance
Oxytocin		Uterus, mammary glands	Uterine contractions; lactation
Vasopressin	Arginine vasopressin, antidiuretic hormone	Kidneys and arterioles	Stimulates water retention; raises blood pressure by contracting arterioles	Insufficient secretion: Diabetes insipidus Oversecretion: Syndrome of inappropriate antidiuretic hormone (SIADH).