bicd150 week3

bicd150 week3 - Handout #3 TSH (Thyroid stimulating...

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Handout #3 TSH (Thyroid stimulating hormone) Synthesis of thyroid hormone 1) Follicular cells synthesize thyroglobulin(TGB) and secrete into colloid 2) Iodide is taken up from blood into the follicular cell via Na+/I- symporter, accumulating I- inside the cell. Iodine is then transported across the apical membrane into colloid via pendrin, which allows I- to move down its concentration gradient 3) Thyroid peroxidase(TPO) iodinate tyrosines on TGB and coupled them to synthesize TH -iodination occurs on carbon 3 monoiodotyrosine (MIT) -iodination occurs on carbon 3,5 diiodotyrosine (DIT) -MIT + DIT = T3 -DIT + DIT = T4 -Reverse T3 inactive (lost iodine on inner ring instead of outer ring) 4) Follicular cells endocytose TGB-I and fuse with lysosomes TGB-I gets cleaved and free T3 and T4 is released into the circulation (bound to transport protein since they are lipid soluble) 5) deiodination of DIT, MIT within the thyroid cell iodine recycled *T3 is more potent because it has much higher affinity for nuclear receptor. Usually, T4 is changed into T3 in cells by DEIODINASES Factors influencing thyroid hormone synthesis TSH (binds to TSH receptor on follicular cells; activate both Gs and Gq) ↑growth of thyroid gland ↑synthesis and secretion of TH (↑iodide uptake, ↑TPO, ↑TGB, ↑lysosomes, etc) Iodine overdose Temporarily inhibit function of follicular cells (inhibit uptake of I- and iodination)
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This note was uploaded on 04/06/2012 for the course BICD 150 taught by Professor Fortes during the Winter '09 term at UCSD.

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bicd150 week3 - Handout #3 TSH (Thyroid stimulating...

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