Skeletal and Articular Systems

Hypophysis/pituitary (hy-POF-ih-sis puh-TOO-ih-ter-ee): The "master" endocrine gland located at the base of the brain; it is anatomically and functionally divided into the glandular adenohypophysis (anterior lobe) and the neural neurohypophysis (posterior lobe). Adenohypophysis (anterior lobe) (ad-uh-noh-hy-POF-ih-sis): The glandular, epithelial portion of the pituitary gland derived from oral ectoderm; it is composed of nests and cords of secretory cells (acidophils, basophils, and chromophobes) that synthesize and release numerous tropic hormones (e.g., ACTH, TSH, GH, FSH, LH, Prolactin). Neurohypophysis (posterior lobe) (noor-oh-hy-POF-ih-sis): The neural portion of the pituitary gland derived from the hypothalamus; it consists primarily of unmyelinated axons and supporting cells (pituicytes) and serves to store and release hormones (Oxytocin and ADH) made by the hypothalamus. Pars distalis (pars dih-STAY-lis): The largest and main part of the adenohypophysis; it contains the majority of the hormone-secreting epithelial cells (acidophils, basophils, chromophobes) that regulate other endocrine glands. Pars nervosa (pars ner-VOH-suh): The largest part of the neurohypophysis; it is composed of nerve endings and glial cells (pituicytes) and is the site where ADH and Oxytocin are released into the blood. Acidophil (AS-ih-doh-fil): A secretory cell type in the pars distalis of the adenohypophysis whose cytoplasm stains intensely with acidic dyes (e.g., eosin, making them appear pink); these cells secrete growth hormone (GH) and prolactin. Basophil (BAY-suh-fil): A secretory cell type in the pars distalis of the adenohypophysis whose cytoplasm stains intensely with basic dyes (e.g., hematoxylin, making them appear purple/blue); these cells secrete tropic hormones (TSH, ACTH, FSH, LH). Chromophobe (KROH-muh-fohb): A cell type in the pars distalis of the adenohypophysis that stains weakly (lacks affinity for both acid and basic dyes); they are thought to be degranulated acidophils or basophils that have recently released their hormones, or may be stem cells. Pars intermedia (pars in-ter-MEE-dee-uh): A narrow, rudimentary zone between the pars distalis and pars nervosa in the pituitary gland; it often contains small cystic spaces filled with colloid and may secrete melanocyte-stimulating hormone (MSH). Colloid (KAH-loyd): A thick, gelatinous, eosinophilic (pink-staining) material found filling the lumens of thyroid follicles or the cystic spaces of the pars intermedia; in the thyroid, it represents the stored precursor of thyroid hormones (thyroglobulin). Neurosecretory body (Herring body) (noor-oh-SEK-ruh-tor-ee BOD-ee): Dilations or swellings found along the axons in the pars nervosa of the neurohypophysis; they represent the storage sites for the hypothalamic hormones (Oxytocin and ADH) before their release. Pituicyte (PIT-oo-ih-syt): The main glial (supporting cell) type of the neurohypophysis (pars nervosa); they are highly branched cells that surround the unmyelinated axons and appear similar to astrocytes. Thyroid follicle (THY-royd FOL-ih-kul): The functional and structural unit of the thyroid gland; it is a spherical structure lined by simple cuboidal follicular cells and filled with proteinaceous colloid (stored thyroglobulin). Follicular cell (fuh-LIK-yoo-ler sell): The principal epithelial cell type lining the thyroid follicle; these cells actively synthesize the precursor protein (thyroglobulin), reabsorb the colloid, and release active thyroid hormones (T3​ and T4​). Parafollicular cell (C-cell) (per-uh-fuh-LIK-yoo-ler sell): A small population of endocrine cells located individually or in small clusters between the thyroid follicles (never lining the follicle lumen); they secrete the hormone calcitonin, which lowers blood calcium levels. Adrenal cortex (uh-DREE-nul KOR-teks): The outer, largest region of the adrenal gland, derived from mesoderm; it is organized into three distinct zones (glomerulosa, fasciculata, and reticularis) and secretes steroid hormones (corticosteroids). Zona glomerulosa (ZOH-nuh gluh-mer-yoo-LOH-suh): The outermost, thin layer of the adrenal cortex; its cells are arranged in small, ovoid clusters (glomeruli) and primarily secrete mineralocorticoids (e.g., aldosterone) to regulate electrolyte balance. Zona fasciculata (ZOH-nuh fuh-sik-yoo-LAY-tuh): The thick, middle layer of the adrenal cortex; its cells are arranged in long, straight cords (fascicles) and primarily secrete glucocorticoids (e.g., cortisol) to regulate metabolism and stress. Zona reticularis (ZOH-nuh ruh-tik-yoo-LAIR-is): The innermost layer of the adrenal cortex, adjacent to the adrenal medulla; its cells are arranged in anastomosing cords (reticulum) and primarily secrete weak androgens (sex steroids). Adrenal medulla (uh-DREE-nul muh-DUL-uh): The central region of the adrenal gland, derived from neural crest cells; it is composed of chromaffin cells that are modified sympathetic ganglion cells and secrete catecholamines (epinephrine and norepinephrine). Sympathetic ganglion cell (adrenal medulla) (Chromaffin cell) (sim-puh-THET-ik GANG-glee-un sell/KROH-muh-fin sell): The modified postganglionic sympathetic neuron found in the adrenal medulla; these large, pale-staining endocrine cells lack axons and instead secrete their neurotransmitters (catecholamines) directly into the blood (endocrine function).