Posterior pituitary

Physiology

• Also called neurohypophysis is part of the endocrine system.
• It is not glandular as is the anterior pituitary. Instead, it is largely a collection of axonal projections from the hypothalamus that terminate behind the anterior pituitary, and serve as a site for the secretion of neurohypophysial hormones (oxytocin and vasopressin) directly into the blood.
• These hormones are created in the hypothalamus and released in the posterior pituitary.

Hormone	Main targets	Effect
Oxytocin	Uterus, mammary glands	Uterine contractions Lactation
Vasopressin ADH	Kidneys and arterioles	Stimulates water retention Raises blood pressure by contracting arterioles

Clinical significance

• Insufficient secretion of vasopressin underlies diabetes insipidus, a condition in which the body loses the capacity to concentrate urine.
• Affected individuals excrete as much as 20 liters of dilute urine per day.
• Oversecretion of vasopressin causes the syndrome of inappropriate antidiuretic hormone (SIADH).