PHS 3341 Lecture 15: Endocrinology 3 - The Thyroid Gland
7 Dec 2016
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Document Summary
Describe the synthesis of thyroid hormones; differentiate between t3 and t4 in terms of production, biologic activity etc. Peroxidase enzyme that is involved in the activation or deactivation of thyroid hormones. Precursor protein is thyroglobulin - stored in thyroid follicles - thyroglobulin rich product is called colloid. Synthesize thyroglobulin and storage in the follicle lumens. Iodine trapping in follicular cells: against >30-folk concentration gradient - active transport of iodide (i-) into cells where oxidized to form i by throperoidase (tpo) Iodination of tyrosine in thyroglobulin: occurs at apical follicle cell-colloid junction (tpo) --> monoiodotyrosine (mit) and diiodotyrosine (dit) Couplings of mit and dit: t4 = 2dit; t3 = 1mit and 1 dit; this occurs while. Mit and dit are still part of the thyroglobulin. Colloid endocytosis: iodinated thyroglobulin molecules taken back into follicular cells by endocytosis; vesicles linked with lysosomes. Cleavage of thyroglobulin to yield hormones for release: small molecules; diffuse out of follicle cells into blood stream; primarily t4.
