Posterior pituitary

Posterior pituitary
Pituitary gland. Posterior pituitary is in blue. Pars nervosa and infundibular stalk are not labeled, but pars nervosa is at bottom and infundibular stalk is at top.)
Median sagittal through the hypophysis of an adult monkey. (Posterior lobe labeled at bottom right.)
Latin	glandula pituitaria, pars nervosa
Gray's	subject #275 1275
Artery	inferior hypophyseal artery
Vein	hypophyseal vein
Precursor	Neural tube (downward-growth of the diencephalon)[1]
MeSH	Pituitary+Gland,+Posterior
Dorlands/Elsevier	Posterior pituitary hormones

The posterior pituitary (or neurohypophysis) comprises the posterior lobe of the pituitary gland and is part of the endocrine system. Despite its name, the posterior pituitary gland is not a gland, per se; rather, it is largely a collection of axonal projections from the hypothalamus that terminate behind the anterior pituitary gland.

Anatomy

The posterior pituitary consists mainly of neuronal projections (axons) extending from the supraoptic and paraventricular nuclei of the hypothalamus. These axons release peptide hormones into the capillaries of the hypophyseal circulation. In addition to axons, the posterior pituitary also contains pituicytes, specialized glial cells resembling astrocytes.

Classification of the posterior pituitary varies, but most sources include the three regions below:

Pars nervosa

Also called the neural lobe or posterior lobe, this region constitutes the majority of the posterior pituitary, and is sometimes (incorrectly) considered synonymous with it. Notable features include Herring bodies and pituicytes.^[2]

Infundibular stalk

Also known as the infundibulum or pituitary stalk, the infundibular stalk bridges the hypothalamic and hypophyseal systems.

Median eminence

This is only occasionally included as part of the posterior pituitary. Other sources specifically exclude it from the pituitary.^[3]

A few sources include the pars intermedia as part of the posterior lobe, but this is a minority view. It is based upon the gross anatomical separation of the posterior and anterior pituitary along the cystic remnants of Rathke's pouch, causing the pars intermedia to remain attached to the neurohypophysis.

Hormones secreted

Hormones known classically as posterior pituitary hormones are synthesized by the hypothalamus. They are then stored and secreted by the posterior pituitary into the bloodstream.

Role in disease

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).

References

Additional images

The posterior pituitary comprises the posterior lobe of the pituitary gland.

Hypothalamic nuclei