Total Iodine content of body is 20-30 mg (20% of which is contained in the thyroid gland) Thyroid Iodine occurs in the following forms: 1) 1% iodide ions (I-) 2) 20-25% incorporated in T3 and T4 3) Rest as thyroglobulin sources Sea foods / Cod liver oil Small amounts of iodide added to table salts prevents iodine deficiency Dietary iodine is converted to iodide and absorbed t3 t4 T3 – Triiodothyronine T4 – Tetraiodothyronine/Thyroxine 1) Trapping of iodide (I-) by Thyroid gland by Iodide Pump (Na+K+ ATPase Pump) 2) Oxidation of Iodide By Iodide peroxidase (thyroperoxidase) 3) Iodination of tyrosine forming 3-monoiodotyrosine (MIT) and 3,5-diiodotyrosine (DIT): 1) Trapping of iodide (I-) by Thyroid gland: by Iodide Pump (Na+K+ ATPase Pump) Na+ pumped out of cells. Na+ reenters along with iodide ions Na+ I- transporter Iodide uptake paralyzed by inhibitor of this pump i.e. oubain Anoxia and substances like cyanide/dinitrophenol which inhibit ATP synthesis also inhibit iodide uptake Enables thyroid gland to concentrate iodide 10-100 times more than the serum on wt. basis oxidation of iodide By Iodide peroxidase (thyroperoxidase) which contains heme; H2O2 utilized in this reaction Iodide oxidized to nascent iodine (Io) or (I3-) which are highly unstable and reactive Storage: T3 and T4 stored in follicles within the molecules of thyroglobulin of colloid material Release: Thyroid cells take up colloid material from the follicles by pinocytosis Ingested colloid material fuses with lysosomes to form phagolysosomes MIT, DIT, T3 and T4 released Only T3 and T4 enter blood stream MIT and DIT are acted upon by enzyme iodotyrosine deiodinase present in thyroid cells resulting in release of I2 from these compounds The I2 liberated is stored and reused for hormone synthesis 30% of T4 is converted to T3 in liver and kidneys hyperthyroidism Graves’ Disease – Most Common Autoimmune Autoantibodies bind to TSH receptors and stimulate the gland to hyperfunction Graves’ Disease – Most Common Autoimmune Autoantibodies bind to TSH receptors and stimulate the gland to hyperfunction