Neuroanatomy of Posterior Pituitary

Also called the neurohypophysis, the posterior pituitary is mainly composed of pituicytes, which support nerve fibers and endings from the hypothalamus.

They originate in the supraoptic and paraventricular nuclei of the hypothalamus and travel through the pituitary stalk.

These are bulbous knobs that contain secretory granules and release hormones into capillaries.

Also called vasopressin, ADH is a posterior pituitary hormone primarily synthesized in the supraoptic nuclei.

Oxytocin is a posterior pituitary hormone primarily synthesized in the paraventricular nuclei.

Cutting the pituitary stalk above the pituitary gland, but leaving the hypothalamus intact, results in the posterior pituitary hormones continuing to be secreted normally after an initial decrease.

The hormones are synthesized in the cell bodies of the supraoptic and paraventricular nuclei and are transported down the fibers to the nerve endings in the posterior pituitary.

When nerve impulses reach the nerve endings, they trigger the release of the stored hormones by exocytosis.

Oxytocin is initially produced in the hypothalamus, but is stored and released from the posterior pituitary gland.

Oxytocin receptors are located on the cell membranes of target cells, not within their nuclei.

The anterior pituitary gland secretes hormones like growth hormone and thyroid-stimulating hormone. Oxytocin is secreted by the posterior pituitary gland.

Oxytocin actually promotes and facilitates labor, as it increases uterine contractions.

Oxytocin's primary role is in uterine contractions and milk release, not intestinal emptying.

A protein that is stored and released along with ADH, but has no known function after secretion.

Both are nine amino acid peptides, with very similar structures.

The collecting ducts temporarily become very permeable to water by inserting channels called aquaporins.

ADH binds to receptors, activating adenylyl cyclase and causing phosphorylation of aquaporins, which then cause the vesicles to be inserted into the apical cell membranes.

A decrease in urine output and an increase in urine concentration.

It causes an increase in urine output, resulting in very dilute urine.

It occurs within 5 to 10 minutes.

The movement of water from an area of high water concentration to an area of low water concentration across a semi-permeable membrane.

A hormone produced in the hypothalamus and stored in the posterior pituitary that helps regulate water balance by increasing water reabsorption in the kidneys.

The concentration of dissolved substances in a solution, measured as the number of moles of solute per liter of solution.

A state in which the body has too little water compared to its electrolytes, leading to increased blood osmolarity.

A state in which the body has too much water compared to its electrolytes, leading to decreased blood osmolarity.

Specialized neurons in the hypothalamus that are sensitive to changes in blood osmolarity and trigger the release of ADH.

A condition in which there is a decrease in blood volume, often due to blood loss or dehydration.

A function of ADH that causes constriction of blood vessels, leading to increased blood pressure.

A condition caused by a lack of ADH, leading to excessive urination (polyuria) and thirst (polydipsia).

Oxytocin is a hormone primarily released by the paraventricular nucleus of the hypothalamus, with a small contribution from the supraoptic nucleus.

Oxytocin's primary function is to stimulate milk ejection from mammary glands and uterine contractions during labor.

During pregnancy, estrogen and progesterone suppress oxytocin secretion, but as these hormones decrease at the end of pregnancy, oxytocin levels rise, initiating uterine contractions and labor.

Oxytocin acts by binding to G-protein coupled receptors on target cells, primarily in the mammary glands and the uterus.

Stretch receptors in the carotid, aortic, and pulmonary arteries detect changes in blood pressure. When these receptors are stretched, they send signals to the hypothalamus, inhibiting ADH release.

Decreased stretch of baroreceptors, indicating low blood pressure, stimulates ADH secretion, leading to increased water retention and blood pressure elevation.