Endocrine System III: Pituitary, Thyroid, and Parathyroid Physiology

Comprehensive vocabulary flashcards covering the hypothalamic-pituitary axis, prolactin, growth hormone physiology and biotechnology, thyroid gland endocrinology, and parathyroid calcium regulation from ANSC 220 Lecture 13.

Hypothalamic-Hypophyseal Portal System

A specialized vascular system consisting of primary and secondary capillary plexuses connected by portal vessels, allowing neuroendocrine hormones from the hypothalamus to directly reach endocrine cells in the anterior pituitary without entering systemic circulation first.

Somatotropes

Endocrine cells in the anterior pituitary that synthesize and secrete growth hormone ($GH$, or somatotropin) to stimulate body growth and regulate metabolism.

Lactotropes

Anterior pituitary cells that secrete prolactin ($PRL$) to stimulate breast development and milk synthesis within the mammary glands.

Thyrotropes

Anterior pituitary endocrine cells that synthesize and secrete thyroid-stimulating hormone ($TSH$) to stimulate thyroid hormone production by the thyroid gland.

Dopamine (DA)

A hypothalamic neuroendocrine hormone produced in the arcuate nucleus ($ARC$) that acts as the primary physiological inhibitor of prolactin ($PRL$) secretion from anterior pituitary lactotropes.

Stricker and Grueter Study (1928)

The pioneering research demonstrating that extracts derived from bovine pituitary glands stimulated lactation in rabbits, providing the first experimental evidence of an anterior pituitary hormone inducing lactation.

Crop "Milk"

A nutritious secretion produced in the crop of certain birds under the control of prolactin ($PRL$) that is fed to their young.

Prolactin-Mediated Chick Stealing

A behavioral effect observed in emperor penguins where elevated circulating concentrations of prolactin ($PRL$) induce non-parental birds to kidnap or adopt unattended chicks.

Growth Hormone-Releasing Hormone (GHRH)

A hypothalamic neuroendocrine hormone produced in the arcuate nucleus ($ARC$) that stimulates somatotropes to produce and secrete growth hormone ($GH$).

Growth Hormone-Inhibiting Hormone (GHIH)

A hypothalamic inhibitory neuroendocrine hormone (also known as somatostatin) produced by the paraventricular nucleus ($PVN$) that suppresses $GH$ secretion from anterior pituitary somatotropes.

Insulin-Like Growth Factors (IGF-1 and IGF-2)

Hormones produced primarily in target tissues such as the liver following $GH$ stimulation that mediate the growth-promoting actions of $GH$ and exert negative feedback on hypothalamic $GHRH$ and pituitary somatotrope $GH$ release.

Gigantism

An endocrine disorder characterized by hypersecretion of growth hormone ($GH$) in childhood prior to the fusion of epiphyseal growth plates, leading to excessive vertical bone growth (exemplified by Robert Wadlow, who reached $8\text{ ft } 11\text{ in}$).

Acromegaly

A condition caused by excessive growth hormone ($GH$) secretion occurring in adulthood after epiphyseal plate closure, resulting in disproportionate thickening of bones, facial structures, and soft tissues (exemplified by wrestler Maurice Tillet).

Laron Syndrome

A genetic condition caused by an insensitivity of the growth hormone receptor ($GHR$), resulting in short stature, low circulating $IGF-1$, and a markedly reduced risk of cancer and diabetes (exemplified by Norman Apolo Ramirez).

Miniature Brahman Condition

A dwarf phenotype identified in Brahman cattle caused by a single nucleotide mutation within the growth hormone gene, as reported by McCormack et al. (2009).

Canine IGF1 Size Variant

A single-nucleotide polymorphism haplotype spanning the $IGF1$ gene on chromosome $15$ that serves as the major genetic determinant of small body size across all domestic small dog breeds.

Protropin

The first recombinant human growth hormone produced using bacteria and plasmid technology, approved by the FDA in 1985 and marketed by Genentech to replace cadaveric pituitary extracts that posed risks of Creutzfeldt-Jakob disease transmission.

Posilac (rbST)

Recombinant bovine somatotropin (sometribove zinc suspension) approved by the FDA in 1993 for over-the-counter use in dairy cattle to increase milk yield by $10\text{--}40\%$ when injected every $14\text{ days}$ starting approximately $2\text{ months}$ post-calving.

AquAdvantage Salmon

The first genetically engineered animal approved for human food consumption, created by modifying Atlantic salmon with a growth hormone gene from Chinook salmon and a promoter sequence from Ocean pout to accelerate growth.

$5'\,3'$ Deiodinase

The peripheral enzyme responsible for converting the prohormone thyroxine ($T_4$) into the biologically active thyroid hormone triiodothyronine ($T_3$) in target tissues.

Thyroid Follicle Colloid

The central gel-filled lumen of a thyroid follicle where thyroglobulin ($\text{Tg}$) is stored and the synthesis of $T_3$ and $T_4$ takes place in the presence of iodine.

Thyroglobulin (Tg)

A large precursor glycoprotein synthesized and secreted into follicular colloid by thyroid principal cells, acting as the protein framework upon which iodine is coupled to synthesize $T_3$ and $T_4$.

Gudernatsch Experiment (1912)

An experimental demonstration showing that feeding sheep thyroid gland extracts to tadpoles triggered premature metamorphosis.

Allen Experiment (1925)

An experimental study demonstrating that surgical destruction of the thyroid gland in tadpoles prevented metamorphosis entirely, causing them to develop into giant tadpoles.

Goiter

An abnormal enlargement of the thyroid gland typically resulting from iodine deficiency-induced loss of $T_3$ and $T_4$ negative feedback, leading to chronic overproduction of $TSH$ and glandular hypertrophy.

Hashimoto's Thyroiditis

An autoimmune disorder in which the immune system targets thyroglobulin ($\text{Tg}$) and thyroid tissue, causing inflammation, swelling of the thyroid gland, and hypothyroidism.

Parathyroid Chief Cells

The cell type within the parathyroid gland that monitors extracellular calcium and secretes parathyroid hormone ($PTH$) in response to low circulating calcium concentrations.

Calcitonin

A peptide hormone secreted by thyroid gland C cells (parafollicular cells) in response to high or optimal blood calcium levels that directly inhibits osteoclast-mediated bone resorption.

Nutritional Hyperparathyroidism

A secondary metabolic condition characterized by elevated parathyroid hormone ($PTH$) due to low dietary calcium or impaired intestinal absorption, leading to bone resorption and diseases such as Rickets in young animals and Bran disease (Bighead) in horses.