Lecture 12: Endocrine System II - Hypothalamus and Pituitary Function

Comprehensive vocabulary flashcards covering the neuroendocrinology of the posterior and anterior pituitary, oxytocin- and vasopressin-mediated reflexes and signaling, diabetes insipidus, the hypothalamic-hypophyseal portal system, and anterior pituitary cell types.

Hypothalamic Nuclei

Groups of specialized neurons within the hypothalamus that respond to sensory input and secrete neuroendocrine hormones to regulate the anterior and posterior pituitary glands.

Ferguson Reflex

A neuroendocrine reflex triggered by the fetus exerting mechanical pressure on the cervix, stimulating afferent neural pathways to the hypothalamus, which causes posterior pituitary oxytocin release and induces smooth muscle (myometrial) contractions via positive feedback until parturition.

Milk Let-Down Reflex

A neuroendocrine reflex initiated by tactile stimulation from nursing young, transmitting sensory signals to the hypothalamus to cause posterior pituitary oxytocin secretion into systemic circulation.

Myoepithelial Cells

Contractile cells wrapping around mammary gland alveoli that contract in response to circulating oxytocin, forcing stored milk into mammary ducts and the gland cistern.

Pitocin

A synthetic pharmaceutical preparation of oxytocin administered to induce or augment uterine contractions during labor and parturition.

Linzell Mammary Transplantation Experiment (1962)

A physiological study by J. L. Linzell demonstrating that denervated and transplanted mammary glands in goats could still undergo milk let-down, confirming that the efferent limb of the milk ejection reflex is blood-borne (humoral) rather than direct neural innervation.

Oxytocin Behavioral Roles

Neuromodulatory actions of oxytocin within the central nervous system that promote maternal care, maternal-infant bonding, trust, sexual pleasure, and lifelong pair bonding (such as in prairie voles, Microtus ochrogaster).

Vasopressin

A posterior pituitary peptide hormone—also termed anti-diuretic hormone (ADH) or arginine vasopressin (AVP)—that regulates systemic water and blood pressure homeostasis by promoting renal water reabsorption and arterial vasoconstriction.

Lysine Vasopressin (LVP)

The specific structural form of vasopressin synthesized and secreted by pigs.

$V_1$ Receptor ($V_1\text{R}$)

A G-protein-coupled receptor located on vascular smooth muscle cells that binds vasopressin to trigger the $G_q$-$\text{PLC}_\beta$-$\text{IP}_3$/$\text{DAG}$ pathway, causing intracellular $\text{Ca}^{2+}$ release, vasoconstriction, increased systemic vascular resistance, and elevated blood pressure.

$V_2$ Receptor ($V_2\text{R}$)

A vasopressin receptor found on renal collecting duct cells that activates adenylyl cyclase via $G_s$, stimulating $\text{cAMP}$ and protein kinase A ($\text{PKA}$) to drive the exocytic insertion of aquaporin-2 ($\text{AQ}_2$) water channels into the apical membrane.

Central Diabetes Insipidus

A disorder characterized by impaired fluid balance resulting from decreased synthesis, storage, or secretion of ADH due to hypothalamic or pituitary damage (from surgery, tumor, trauma, illness) or genetic lesions.

Brattleboro Rat

A laboratory rat model possessing an inherited mutation in the vasopressin gene; it exhibits diabetes insipidus and urinates $70\% \text{ to } 125\%$ of its body weight in water daily.

Polyuria

The production and excretion of abnormally large volumes of dilute urine, typically resulting from absent or deficient vasopressin action.

Polydipsia

Excessive and persistent drinking behavior driven by profound thirst to compensate for severe urinary water losses.

Hypothalamic-Hypophyseal Portal System

A specialized local circulatory network—comprising the superior hypophyseal artery (SHA), primary capillary plexus (PPP), portal vessels (PV), and secondary capillary plexus (SPP)—that delivers releasing and inhibiting hormones directly to anterior pituitary cells without dilution in systemic circulation.

Somatotrope

A specialized anterior pituitary cell type responsible for the synthesis and secretion of growth hormone (GH).

Thyrotrope

An anterior pituitary endocrine cell that synthesizes and secretes thyroid-stimulating hormone (TSH).

Corticotrope

An anterior pituitary cell type that produces and secretes adrenocorticotropic hormone (ACTH) to stimulate cortisol synthesis in the adrenal cortex.

Lactotrope

An endocrine cell in the anterior pituitary that synthesizes and secretes prolactin (PRL) to promote breast growth and milk secretion.

Gonadotrope

An anterior pituitary cell type that synthesizes and releases luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to govern gonadal function and gametogenesis.

Dopamine (DA)

A neuroendocrine neurotransmitter released by the hypothalamic arcuate nucleus (ARC) that acts tonically on lactotropes to inhibit prolactin secretion.

Stricker and Grueter Experiment (1928)

A landmark study proving that bovine anterior pituitary extracts could induce lactation in pseudopregnant rabbits, providing the first experimental evidence of an anterior pituitary hormone stimulating lactation.

Crop "Milk"

A nutrient-rich epithelial lining secretion synthesized in the crop of certain birds under the influence of anterior pituitary prolactin to nourish offspring.