Posterior Pituitary Gland and ADH Regulation

Vocabulary practice flashcards covering posterior pituitary endocrinology, ADH regulation, oxytocin reflexes, diabetes insipidus, SIADH, and craniopharyngioma.

Supraoptic Nucleus (SON)

The hypothalamic nucleus where antidiuretic hormone (ADH) originates before being transported to the posterior pituitary.

Paraventricular Nucleus (PVN)

The hypothalamic nucleus where oxytocin is primarily synthesized prior to its axonal transport to the posterior pituitary.

Neurophysin II

The specific carrier protein that transports antidiuretic hormone (ADH) down nerve axons from the supraoptic nucleus to the posterior pituitary gland.

Neurophysin I

The carrier protein responsible for transporting oxytocin from the paraventricular nucleus down axonal projections to the posterior pituitary.

V1 Receptor

The vascular smooth muscle receptor through which ADH exerts its vasoconstrictor action, earning it the name vasopressin.

V2 Receptor

The renal tubular receptor through which ADH stimulates adenylyl cyclase activity ($\text{cAMP}$) to exert its antidiuretic effect.

Hypothalamo-Hypophyseal Tract

The bundle of nerve axons passing through the infundibulum that delivers ADH and oxytocin from the hypothalamic nuclei to the posterior pituitary for storage and release.

Central (Neurogenic) Diabetes Insipidus

A disorder caused by complete or partial failure of ADH secretion due to diseases of the hypothalamus or posterior pituitary, characterized by an increase in urine osmolarity after exogenous ADH administration.

Nephrogenic Diabetes Insipidus

A condition resulting from complete or partial failure of the kidneys to respond to ADH due to defects in V2 receptors or aquaporin water channels, where urine osmolarity fails to increase following exogenous ADH administration.

Lithium Carbonate

A medication used to treat bipolar mood disorders that can cause an acquired defect in the apical water channel Aquaporin 2 in collecting ducts, inducing nephrogenic diabetes insipidus.

Polyuria

The excretion of abnormally large volumes of urine ($3\text{ to }20\,\text{L/day}$) due to impaired renal water reabsorption in the collecting ducts.

Polydipsia

A clinical symptom of intense, excessive thirst resulting from stimulation of the hypothalamic thirst center in response to water loss.

Syndrome of Inappropriate ADH Secretion (SIADH)

A disorder characterized by autonomous, abnormally excessive secretion of ADH, causing elevated ECF volume, low plasma osmolarity, hypertonic urine, low urine output, and negative free water clearance.

Arginine Vasopressin (AVP)

A synthetic analog of ADH with marked antidiuretic activity and minimal pressor activity, used therapeutically to treat neurogenic diabetes insipidus.

Free $\text{H}_2\text{O}$ Clearance

A parameter measuring the volume of solute-free water cleared by the kidneys; it is negative during water deprivation and SIADH, and positive in diabetes insipidus and primary polydipsia.

Milk Ejection Reflex

A neuroendocrine reflex initiated by infant suckling in which afferents from the 4th–6th intercostal nerves stimulate hypothalamic oxytocin release, contracting mammary myoepithelial cells and causing milk let-down.

Myoepithelial Cells

Specialized contractile cells surrounding mammary alveoli that contract in response to oxytocin to eject milk into the mammary ducts.

Parturition Reflex

A positive feedback labor reflex in which stretching of the cervix by the fetal head triggers oxytocin release from the paraventricular nucleus, stimulating uterine myometrial contractions.

Craniopharyngioma

A slow-growing, extra-axial, epithelial-squamous, calcified cystic tumor arising from remnants of the craniopharyngeal duct or Rathke cleft, located in the pituitary stalk with potential optic and endocrine compromise.

Complete Central Diabetes Insipidus

A diagnosis confirmed during a water deprivation test when urine osmolality increases by $>50\%$ after exogenous vasopressin administration.

Partial Central Diabetes Insipidus

A diagnosis confirmed during a water deprivation test when urine osmolality shows a modest rise of $>10\%$ but $<50\%$ following exogenous vasopressin administration.