IMED3004 Lecture Notes - Lecture 13: Reuptake, Goitre, Hyperthyroidism
Thyroid peroxidase oxidises iodide (i-) to iodine (i2) Two large lateral lobes (3x5cm) connected by a thin isthmus (1. 25x1. 25cm). Thyroid gland structure: (~0. 5mm diameter = big) epithelial cells lining the follicle. with thyroglobulin (glycoprotein) by a dense capillary network. Thyroid hormones: derived from tyrosine (aa, thyroxine t4, triiodothyronine t3. Thyroxine (t4: major secretary product (>90%), low biological activity. usually transformed t3 within target cells. Thyroid hormones need large amounts of iodine (i2). Absorbed as iodide (i-) and oxidised to iodine (thyroid peroxidase). Thyroid glands have powerful iodide pumps to concentrate iodine within the thyroid gland. ([i-] in follicular cells 20-50x > plasma: thyroglobulin precursor (tgb) Thyroglobulin precursor major component for t3 and t4 synthesis. Big protein (660kd) stores ths as a colloid (4-5 ths per. Tgb: made in follicle cells immediately exocytosed into follicle lumen. Thyroid hormone biosynthesis & secretion: oxidation of iodide, coupling of tyrosine residues. Iodination of tyrosine residues: dit+dit=t4, mit+dit=t3, endocytosis and digestion of colloid.