|Precursor||Neural tube (downward-growth of the diencephalon)|
|Artery||inferior hypophyseal artery|
|Latin||Pars nervosa glandulae pituitariae,|
pars nervosa hypophyseos,
lobus posterior hypophyseos
The posterior pituitary (or neurohypophysis) is 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 serve as a site for the secretion of neurohypophysial hormones (oxytocin and vasopressin) directly into the blood. The hypothalamic-neurohypophyseal system is composed of the hypothalamus (the paraventricular nucleus and supraoptic nucleus), posterior pituitary, and these axonal projections.
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 neurohypophyseal capillaries, from there they get into the systemic circulation (and partly back into 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:
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.
Two hormones are classically considered as being related to the posterior pituitary: oxytocin and vasopressin. These hormones are created in the hypothalamus and released in the posterior pituitary. After creation, they are stored in neurosecretory vesicles regrouped into Herring bodies before being secreted in the posterior pituitary via the bloodstream.
|Hormone||Other names||Symbol(s)||Main targets||Effect||Source|
|Oxytocin||OT||Uterus, mammary glands||Uterine contractions; lactation||supraoptic and paraventricular nuclei|
|Vasopressin||Arginine vasopressin, antidiuretic hormone||VP, AVP, ADH||Kidneys and arterioles||Stimulates water retention; raises blood pressure by contracting arterioles||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).
oThe hypothalamic-neurohypophyseal system secretes two peptide hormones directly into the blood, vasopressin and oxytocin. ...
oThe hypothalamic-pituitary-adrenal (HPA) axis. It comprises corticotropin-releasing factor (CRF), released by the hypothalamus; adrenocorticotropic hormone (ACTH), released by the anterior pituitary; and glucocorticoids, released by the adrenal cortex.
oThe hypothalamic-pituitary-thyroid axis consists of hypothalamic thyrotropin-releasing hormone (TRH); the anterior pituitary hormone thyroid-stimulating hormone (TSH); and the thyroid hormones T3 and T4.
oThe hypothalamic-pituitary-gonadal axis comprises hypothalamic gonadotropin-releasing hormone (GnRH), the anterior pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and the gonadal steroids.