Hormones (TH)

Thyroid Hormones (TH): T3: Active carries out PD effect 30-40 mcg/day most is synthesized outside the thyroid gland in the peripheral tissues T4: Inactive 60-100 mcg/day rT3: Inactive produced through metabolism of other THs Synthesis of Thyroid Hormone Thyroglobulin (contains 134 tyrosine) is synthesized and discharged into the lumen. Only a handful of these are actually used. Iodides (I-) are actively taken into the cell, oxidized to iodine (I2), and released into the lumen. Thyroid peroxidase attaches iodine to tyrosine, forming MIT (monoiodotyrosine), and DIT (diiodotyrosine). Thyroid peroxidase links together to form T3 and T4. Endocytosis of T3 and T4 are cleaved in lysosomes and diffuse into the bloodstream. Key Notes: almost all T3 + T4 are bound to plasma protein ~70% TBG ~15% Albumin ~15% TBPA T4 has a longer half-life (~7 days) vs. T3 (~1.5 days) Thyroid produces more T4 ~30-40% T4 -> T3 primarily in peripheral tissues via deiodination Thyroid Function Tests (TFTS): S most accurate FT4 and FT3 are the most reliable tests for assessing thyroid hormone concentrations Thyroid gland autoantibodies indicate autoimmune process Thyroglobulin Ab (TgAb) where it proteins in the colloid space a backbone for T3+T4 to attach Thyroid Peroxidase Ab (TPOAb) = key enzyme in iodination! Coupling phases in production of T3+T4 Thyroid Stimulating Ab (TSAb) Thyroid Receptor Stimulating Ab (TRAb) Factors that Affect TFTs: Euthyroid Patients Mechanism Increase TBG binding capacky Maine that inersans in the Mised Me the le - recalt inat over 99%, ef these d in the pissens Thyroid function test Increase T14 Increase T13 Normal TSH Normal FT41, FT4 Normal FT31, FT3 Decrease T8G binding capacity / displacement 74 from binding sites Decrease T14 Decrease T73| Normal TSH Normal FT4,, FT4 Normal F131, 913| Decrease per pheral T4 to T3 corversion Decreased T13 Normal TT4 Normal IT41, FT4 Normal TSH Mechanism Decrease pituitary and peripheral 74 to T3 Thyroid function test Increase T74 Decrease T13 Increase TSH (transient) Increase FT41 Increase 14 clearance by fecal loss / increase Decrease 114 ne are in the bod/Decrease FT41 Normal or increase TSH Normal or decrease FT4 Normal or decrease TT3 Factor Estrogens, tamoxiten, ralexifere Cral contraceton Feroin, Methadone Gofibrate Active hepititis Genetic increase in TBG Androgens Salicyates High-dose furosemide Canasol Clucocorticoids Nephrotic syndrome Garhosis/heeatic fa has PTU Propranoicl Clacocorticoids Factor lodinated contrast media Amiodarone Non-thyroidal liness Phenytoin Phenobarbital Carbamazepine Cholestyramine Colestipol Rifampin Bexaratene "Euthyroid Sick Sundrome" Mechanism Decrease TSH secretion Factor Dopamine, Levodopa Bromocriptine, cabergoline, pramiprexole Glucocorticoids Octreotide Metformin Increase TSH secretion Metoclopramide Domperidone Euthyrodism i Non-Thyroid Illness syndrome: - TFTs Come back abnormal even though pt does not have a thyroid disorder " Chronically ill or hospitalived pes - the sicker +he pt the more abnomal the results l commonly triggered by serious systemie siness, starvation, infecion, sepsis, deute prichosis waltered ToG levels will effect acute hepaths, preghana drugs (EST, Ocs, tamoxifen, ratoxifen, heroin / methadone)