The Posterior Pituitary Gland consists mainly of neuronal projections (axons) extending from the supraoptic and paraventricular nuclei of the hypothalamus that secrete peptide hormones into the capillaries of the hypophyseal circulation.
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:
|pars nervosa, or neural lobe, or posterior lobe||This region consistutes the majority of the posterior pituitary, and is sometimes (incorrectly) considered synonymous with it. Notable features include Herring bodies and pituicytes.|
|infundibular stalk||Also known as the "infundibulum" or "pituitary stalk". The term "hypothalamic-hypophyseal tract" is a near-synonym, describing the connection rather than the structure.|
|median eminence||This is only occasionally included as part of the posterior pituitary. Other sources specifically exclude it from the pituitary.|
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.
|Oxytocin||-||-||Uterus, mammary glands||Uterine contractions; lactation||supraoptic and paraventricular nuclei|
|Vasopressin||Arginine vasopressin, argipressin, antidiuretic hormone||AVP, ADH||Kidneys or Arterioles||Stimulates water retention; raises blood pressure by contracting arterioles, induces male aggression||supraoptic and paraventricular nuclei|
Oversecretion of vasopressin causes the syndrome of inappropriate antidiuretic hormone.