Neurohypophysis Anatomy and Function Quiz

Neurohypophysis: Structure and Function

Introduction

The human body maintains its internal environment in a narrow range through a variety of mechanisms. One such mechanism involves the neurohypophysis, also known as the posterior lobe of the pituitary gland. It plays a crucial role in maintaining water balance and reproductive function. This article provides an overview of the anatomy, physiology, and pathophysiology of the neurohypophysis and its main components, arginine vasopressin (AVP) and oxytocin.

Development of the Neurohypophysis

During embryonic development, the neurohypophysis arises from the neuroectodermal layer called the infundibulum, which grows inferiorly from the floor of the diencephalon. After approximately 35 to 40 days of gestation, the vesicle that later becomes the neurohypophysis separates from the stomodeum.

Components of the Neurohypophysis

The neurohypophysis is divided into three parts: the supraoptic and paraventricular nuclei of the hypothalamus, the supraoptico-hypophyseal tract, and the posterior pituitary. The hormones released by the neurohypophysis are oxytocin and AVP. These hormones are synthesized from the precursors preprooxyphysin and prepro-oxytocin.

Arginine Vasopressin (AVP)

Arginine vasopressin, also known as antidiuretic hormone (ADH), is primarily responsible for maintaining water balance in the body. It acts as a water-conserving hormone by regulating the water permeability of the collecting ducts in the kidneys.

The production of AVP is regulated by two primary mechanisms. First, the presence of an osmotic gradient between the blood and cerebrospinal fluid stimulates the release of AVP from the neurohypophysis. Second, the stretching of baroreceptors in response to increased blood pressure can also trigger AVP release. Once released, AVP travels through the general circulation to reach its target sites, mainly the kidneys.

Oxytocin

Oxytocin is another hormone produced by the neurohypophysis, which plays a significant role in childbirth and lactation. During labor, oxytocin triggers uterine contractions and helps expel the baby. Once the baby is born, oxytocin facilitates milk ejection from the breasts.

In addition to these well-known functions, oxytocin has been implicated in other physiological processes such as social bonding, memory formation, and stress reduction.

Pathophysiology of the Neurohypophysis

Disruptions in the production or action of either AVP or oxytocin can lead to several health conditions. For instance, deficiencies in AVP are associated with central diabetes insipidus, characterized by excessive dilute urine and thirst. On the other hand, excess AVP production results in the syndrome of inappropriate antidiuretic hormone (SIADH), which leads to water retention and hypervolemic hyponatremia. Overproduction or underproduction of oxytocin can also affect reproduction, leading to infertility or complications during childbirth and lactation.