Integrated Pituitary and Hypothalamus High-Yield Revision

A comprehensive collection of high-yield vocabulary flashcards reviewing the anatomy, physiology, signaling pathways, pathology, diagnostic tests, and pharmacology of the pituitary gland and hypothalamus.

Primary endocrine defect

Target gland failure characterized by a low target hormone level with a high trophic hormone level.

Secondary endocrine defect

A pituitary-level failure characterized by a low target hormone level accompanied by a low or inappropriately normal trophic hormone level.

Tertiary endocrine defect

A defect characterized by reduced hypothalamic drive and a secondary reduction in both pituitary and downstream target hormones.

Bitemporal hemianopia

The classic visual field defect resulting from superior enlargement of a sellar pituitary mass compressing the overlying optic chiasm.

Rathke pouch

An upward outpocketing of oral ectoderm from the roof of the primitive mouth that gives rise to the anterior pituitary (adenohypophysis).

Herring bodies

Neurosecretory accumulations in the neurohypophysis that represent expanded axonal terminals storing oxytocin and ADH.

Pituicytes

Supportive, modified glial cells located throughout the posterior pituitary (neurohypophysis).

Magnocellular neurons

Large hypothalamic neurons situated within the supraoptic and paraventricular nuclei that synthesize ADH and oxytocin and project direct axonal tracts to the neurohypophysis.

Parvocellular neurons

Small hypothalamic neurons that release hypophysiotropic regulating hormones into the median eminence primary capillary plexus to supply the anterior pituitary via portal veins.

Aquaporin-2 (AQP2)

Water channels that are inserted into the apical membrane of collecting duct principal cells via $V_2$-mediated Gs/adenylyl cyclase/cAMP/PKA signaling to facilitate water reabsorption.

Neurophysins

Carrier proteins packaged alongside nonapeptide neurohormones (ADH and oxytocin) within secretory vesicles during axonal transport from the hypothalamus to the posterior pituitary.

Somatotropin

A 191-amino-acid anterior pituitary peptide secreted by somatotrophs under PIT1 lineage direction that acts through a type I cytokine receptor and the JAK2/STAT signaling pathway.

Laron syndrome

A hereditary form of severe growth failure caused by a defective growth hormone receptor, characterized by low serum IGF-1 levels despite normal or elevated circulating GH levels.

Gigantism

A clinical syndrome of extreme linear skeletal growth caused by growth hormone excess occurring prior to epiphyseal plate fusion in children or adolescents.

Acromegaly

A disorder caused by growth hormone hypersecretion occurring after epiphyseal plate fusion, causing enlargement of hands, feet, jaw, and soft tissues along with metabolic dysfunction.

Simmonds disease

Severe destructive lesion of the pituitary gland resulting in marked cachexia and global hypopituitarism.

Diabetes insipidus (DI)

A disorder of water balance defined by hypotonic polyuria (often $>50\,\text{mL/kg/day}$) and dilute urine ($<300\,\text{mOsm/kg}$) secondary to impaired ADH synthesis, release, or renal response.

Central diabetes insipidus

A form of diabetes insipidus caused by deficient hypothalamic-pituitary AVP secretion that exhibits a large increase in urine osmolality (often $>50\%$) after desmopressin administration.

Nephrogenic diabetes insipidus

A form of diabetes insipidus caused by renal resistance to AVP, demonstrating minimal or no concentration response to exogenous desmopressin.

Gestational diabetes insipidus

A transient form of diabetes insipidus during pregnancy caused by placental vasopressinase degrading endogenous AVP; it responds to enzyme-resistant desmopressin.

Copeptin

A stable nonapeptide-associated peptide secreted in equimolar amounts with AVP, utilized as a surrogate diagnostic biomarker to distinguish polyuria-polydipsia etiologies.

Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

A water-retaining syndrome caused by non-physiological ADH release, presenting with hypotonic hyponatremia and inappropriately concentrated urine.

Pituitary neuroendocrine tumor (PitNET)

A neuroendocrine neoplasm of adenohypophyseal cells (formerly pituitary adenoma) classified by transcription factor lineage (PIT1, TPIT, SF1) and size ($<1\,\text{cm}$ micro vs. $\ge 1\,\text{cm}$ macro).

Craniopharyngioma

A benign, often calcified suprasellar epithelial neoplasm originating from remnants of Rathke pouch that can impair vision and hypothalamo-pituitary endocrine function.

Sheehan syndrome

Postpartum anterior pituitary ischemic necrosis triggered by severe obstetric hemorrhage and hypotension, classically presenting with failure of lactation and multiple hormonal deficiencies.

Pituitary apoplexy

A medical emergency caused by acute hemorrhage or infarction within a pituitary lesion, characterized by sudden severe headache, visual field defects, and acute panhypopituitarism.

Desmopressin (DDAVP)

A synthetic selective $V_2$ receptor agonist that stimulates renal collecting duct water reabsorption via apical AQP2 insertion without significant vascular $V_1$ pressor activity.

Pegvisomant

A peripheral growth hormone receptor antagonist that lowers serum IGF-1 levels in acromegaly without causing regression of the underlying pituitary tumor.

Mecasermin

A recombinant form of human IGF-1 indicated for severe primary GH resistance (Laron syndrome); it carries a major adverse risk of hypoglycemia.

Octreotide

A synthetic somatostatin analogue that binds somatostatin receptors coupled to Gi to inhibit GH release in patients with acromegaly.

Cosyntropin

A synthetic derivative of ACTH that stimulates melanocortin 2 receptors ($\text{MC2R}$) and cAMP production, used in dynamic diagnostic testing to evaluate adrenal reserve.

Tolvaptan

An oral non-peptide vasopressin $V_2$ receptor antagonist utilized for the management of euvolemic hyponatremia in SIADH that carries a warning for hepatotoxicity.