Steps in the Synthesis and Secretion of Thyroid Hormone Process Diagrams Step-by-Step Copyright © 2007 by John Wiley & Sons, Inc.

Portion of thyroid follicle Follicular cell Blood capillary Iodide trapping I–I– Blood capillary Blood plasma Key: I – = Iodide; I 2 = Iodine TGB = thyroglobulin TBG = thyroxine-binding globulin Colloid 1 I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I–

Portion of thyroid follicle Follicular cell Blood capillary TGB Secretory vesicles Golgi complex Rough ER Synthesis of TGB Iodide trapping I–I– Blood capillary Blood plasma Key: I – = Iodide; I 2 = Iodine TGB = thyroglobulin TBG = thyroxine-binding globulin Colloid 1 2 I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I–

Portion of thyroid follicle Follicular cell Blood capillary TGB Oxidation of iodide Secretory vesicles Golgi complex Rough ER Synthesis of TGB Iodide trapping I–I– Blood capillary Blood plasma Key: I – = Iodide; I 2 = Iodine TGB = thyroglobulin TBG = thyroxine-binding globulin I2I2 Colloid I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I–

Iodination of tyrosine Portion of thyroid follicle Follicular cell Blood capillary TGB Tyrosine Oxidation of iodide Secretory vesicles Golgi complex Rough ER Synthesis of TGB Iodide trapping I–I– Blood capillary Blood plasma Key: I – = Iodide; I 2 = Iodine TGB = thyroglobulin TBG = thyroxine-binding globulin I2I2 Colloid I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I–

Iodination of tyrosine Portion of thyroid follicle Follicular cell Blood capillary Coupling of T 1 and T 2 Colloid TGB Tyrosine T1T1 T2T2 T4T4 Oxidation of iodide Secretory vesicles Golgi complex Rough ER Synthesis of TGB Iodide trapping I–I– Blood capillary Blood plasma Key: I – = Iodide; I 2 = Iodine TGB = thyroglobulin TBG = thyroxine-binding globulin I2I2 Colloid T3T I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I–

Iodination of tyrosine Portion of thyroid follicle Follicular cell Blood capillary Coupling of T 1 and T 2 Colloid TGB Tyrosine T1T1 T2T2 T4T4 Oxidation of iodide Lysosome Secretory vesicles Golgi complex Rough ER Synthesis of TGB T3T3 Iodide trapping I–I– Blood capillary Blood plasma Key: I – = Iodide; I 2 = Iodine TGB = thyroglobulin TBG = thyroxine-binding globulin I2I2 Pinocytosis and digestion of colloid Colloid T4T4 T3T I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I–

Iodination of tyrosine Portion of thyroid follicle Follicular cell Blood capillary Coupling of T 1 and T 2 Colloid TGB Tyrosine T1T1 T2T2 T4T4 Oxidation of iodide Lysosome Secretory vesicles Golgi complex Rough ER Synthesis of TGB T3T3 Iodide trapping Secretion of thyroid hormones T3T3 T4T4 I–I– Blood capillary Blood plasma TBG T3T3 Key: I – = Iodide; I 2 = Iodine TGB = thyroglobulin TBG = thyroxine-binding globulin I2I2 Pinocytosis and digestion of colloid Colloid T4T4 T4T4 T3T I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I–

Iodination of tyrosine Portion of thyroid follicle Follicular cell Blood capillary Coupling of T 1 and T 2 Colloid TGB Tyrosine T1T1 T2T2 T4T4 Oxidation of iodide Lysosome Secretory vesicles Golgi complex Rough ER Synthesis of TGB T3T3 Iodide trapping Secretion of thyroid hormones T3T3 T4T4 I–I– Blood capillary Blood plasma TBG T3T3 Key: I – = Iodide; I 2 = Iodine TGB = thyroglobulin TBG = thyroxine-binding globulin Transport in blood I2I2 Pinocytosis and digestion of colloid Colloid T4T4 T4T4 T3T I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I– I–I–