Review the steps of T3 and T4 synthesis and secretion by completing each sentenc

Question

Review the steps of T3 and T4 synthesis and secretion by completing each sentence at right with one or more terms at left. Synthesis begins when circulating across the basolateral membrane of the follicle cell is cotransported with Na* odide trapping Once inside the follicular epithelial cell, the negatively charged iodide cannot diffuse back into the interstitial fluid, this is known as iodide The trapped IF diffuses down its electrochemical gradient to the apical membrane of the endocytosis monoiodotyrosine (MIT) diiodotyrosine (DIT) interstitial fluid blood Next, his transported into the by an integral membrane protein called where it is then oxidized and attached to rings of proteins within The iodinated ring of one or diodotyrosine (DIT) is added to a at another spot on the thyroglobulin molecule thyroglobulin One MIT coupled to one DIT creates molecules create while two coupled DIT pendrin When thyroid hormone is required in the blood, portions of the colloid with its iodinated thyroglobulin are engulfed into the follicular epithelial cell by colloid follicular epithelial cells tyrosines in the follicular The thyroglobulin is brought into contact with epithelial cell interior. Enzymatic proteolysis of thyroglobulin releases T3 and T4, which then diffuse out of the follicular epithelial cell into the and then into the

Explanation / Answer

1. Synthesis begins when when circulating iodide is transported across the basolateral membrane of the follicle cell.

2. Once inside the follicular epithelial cell , the negatively charged iodide can not diffuse back into the interstitial fluid . This is known as iodide trapping.

3. The trapped iodide diffuses down its electrochemical gradient to the epical membrane of follicular epithelial cells.

4. Next, I- transported into the follicle by an integral membrane protien called pendrin where it is then oxidised and attached to the rings of tyrosines within thyroglobulin protien.

5. The iodinated ring of one tyrosine or diiodotyrosine is added to a MIT at a another spot on the thyroglobulin molecule.

6. One MIT coupled to one DIT creates T3 , while two coupled DIT mooecule create T4.

7. When thyroid hormones is required in the blood , protiens of the colloid with its iodinated thyroglobulin are engulfed into the follicular epithelial cells by endocytosis.

8. The thyroglobulin brought into contact with lysosome in the follicular cell interior.

9. Enzymatic proteolysis of thyroglobulin releases T3 and T4 which diffuse out of the follicular epithelial cell into the interstitial fluid then into the blood.

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