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.)
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.
Classification of the posterior pituitary varies, but most sources include the three regions below:
Region
Description
pars nervosa, or neural lobe, or posterior lobe[2]
This region consistutes the majority of the posterior pituitary, and is sometimes (incorrectly) considered synonymous with it. Notable features include Herring bodies and pituicytes. [3]
Also known as the "infundibulum" or "pituitary stalk". The term "hypothalamic-hypophyseal tract" is a near-synonym, describing the connection rather than the structure.
This is only occasionally included as part of the posterior pituitary.[4] Other sources specifically exclude it from the pituitary.[5]
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.
Major 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.
Insufficient secretion of vasopressin is central to diabetes insipidus, in which the body loses the capacity to concentrate urine. Affected individuals excrete as much as 20 L of dilute urine per day.
