|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||Pars nervosa glandulae pituitariae,
pars nervosa hypophyseos,
lobus posterior hypophyseos
|Gray's||subject #275 1275|
|Artery||inferior hypophyseal artery|
|Precursor||Neural tube (downward-growth of the diencephalon)|
|Dorlands/Elsevier||Posterior pituitary hormones|
The posterior pituitary (or neurohypophysis) comprises the posterior lobe of the pituitary gland which is part of the endocrine system. The posterior pituitary 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 is also a store for the later release of neurohypophysial hormones.
The posterior pituitary consists mainly of neuronal projections (axons) of magnocellular neurosecretory cells extending from the supraoptic and paraventricular nuclei of the hypothalamus. These axons store and release neurohypophysial hormones oxytocin and vasopressin into the neurohypohyseal capillaries, from there they get into the systemic circulation (and partly back to the hypophyseal portal system). In addition to axons, the posterior pituitary also contains pituicytes, specialized glial cells resembling astrocytes assisting in the storage and release of the hormones.
Classification of the posterior pituitary varies, but most sources include the two regions below:
- Pars nervosa
- Also called the neural lobe or posterior lobe, this region constitutes the majority of the posterior pituitary and is the storage site of oxytocin and vasopressin. Sometimes (incorrectly) considered synonymous with the posterior pituitary, the pars nervosa includes Herring bodies and pituicytes.
- Infundibular stalk
- Also known as the infundibulum or pituitary stalk, the infundibular stalk bridges the hypothalamic and hypophyseal systems.
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 known classically as posterior pituitary hormones are synthesized by the hypothalamus. They are then stored in neurosecretory vesicles regrouped into Herring bodies before being secreted by the posterior pituitary into the bloodstream.
|Hormone||Other names||Symbol(s)||Main targets||Effect||Source|
|Oxytocin||Pitocin (trade name)||OT||Uterus, mammary glands||Uterine contractions; lactation||supraoptic and paraventricular nuclei|
|Vasopressin||Antidiuretic hormone, arginine vasopressin, argipressin||VP, AVP, ADH||Kidneys or Arterioles||Stimulates water retention; raises blood pressure by contracting arterioles, induces male aggression||supraoptic and paraventricular nuclei|
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).
This article uses anatomical terminology; for an overview, see anatomical terminology.