Ms. Anu Sebastian is an Assistant Professor in the Department of Pharmacology at Nirmala College of Pharmacy in Muvattupuzha, Ernakulam, Kerala. The document outlines the 8 key steps in the synthesis of thyroid hormones: 1) Iodide trapping, 2) Thyroglobulin synthesis, 3) Iodide oxidation, 4) Iodination of tyrosine, 5) Coupling of monoiodotyrosine and diiodotyrosine, 6) Pinocytosis and digestion of colloid droplets, 7) Secretion of thyroid hormones triiodothyronine and thyroxine into blood circulation, and 8) Transport of hormones via thyroxine binding proteins in the

1. Ms.Anu Sebastian: B.Pharm; M.Pharm
Assistant Professor,
Dept. Of Pharmacology
Nirmala College Of Pharmacy
Muvattupuzha,Ernakulam,Kerala

2. STEPS INVOLVED
 IODIDE TRAPPING
 SYNTHESIS OF THYROGLOBULIN(TGB)
 OXIDATION OF IODIDE
 IODINATION OF TYROSINE
 COUPLING OF T1 & T2
 PINOCYTOSIS & DIGESTION OF COLLOIDS
 SECRETION OF THYROID HORMONES
 TRANSPORT IN THE BLOOD

3. IODIDE TRAPPING
Follicular cells trap iodide ions by Na- Iodide transporter.
SYNTHESIS OF THYROGLOBULIN(TGB)
 TGB is large glycoprotein synthesized in the rough
endoplasmic reticulum of follicular cells.
 Modified & stored in secretory vesicles by Golgi apparatus.
 Then these are released into the lumen of thyroid follicles.

4. OXIDATION OF IODIDE
 For the synthesis of thyroid hormones, the aminoacids (ie
Tyrosine ) of TGB need to be iodinated.
 Negatively charged iodide ions cant iodinate tyrosine.So they
undergo oxidation by the enzyme peroxidase to form iodine.
IODINATION OF TYROSINE
 If one iodine react with tyrosine –forms monoiodotyrosine.
 If two iodine react with tyrosine – forms Diiodotyrosine,
Colloid – The TGB with attached iodine atom is stored in the
lumen of the thyroid follicle.

5. COUPLING T1 & T2
 Two molecules of T2 join to form T4(Tetraiodotyronine)
 One molecule of T2 & one molecule of T1 join to form
T3(Triiodotyronine)
PINOCYTOSIS AND DIGESTION OF COLLOIDS
 Droplets of colloid re-enter follicular cells by pinocytosis.
 It will fuse with lysosome .
 The digestive enzyme protease in lysosome breakdown
Thyroglobulin and release T3 & T4.

6. SECRETION OF THYROID HORMONES
 As T3 & T4 are lipid soluble,they diffuse through the plasma
membrane and reaches blood circulation.
TRANSPORT IN THE BLOOD
 T3 & T4 are transported in the blood by combining with
transport proteins in blood ie Thyroxine binding proteins.

8. THANK YOU