Thyroid hormone

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Thyroid hormone

  1. 2. T 4 & T 3 – Iodine containing derivatives of thyronine T 4 -thyroxine ( 3,5,3ˈ,5ˈ -tetraiodothyronine) T 3 -triiodothyronine (3,5,3ˈ triiodothyronine) SYNTHESIS Thyroglobulin molecule-glycoprotein synthesized by thyroid cells MW-660 KDa.
  2. 3. <ul><li>Iodine uptake </li></ul><ul><li>2. Oxidation and Iodination </li></ul><ul><li>Coupling </li></ul><ul><li>Storage and release </li></ul><ul><li>5. Peripheral conversion of T 4 to T 3 </li></ul>
  3. 5. <ul><li>Plasma protein bound- 0.03-0.08 % T 4 </li></ul><ul><li>0.2-0.5% T 3 </li></ul><ul><li>Binding occurs to 3 plasma proteins </li></ul><ul><li>Thyroxine binding globulin (TGB) </li></ul><ul><li>Thyroxine binding prealbumin (transthyretin) </li></ul><ul><li>Albumin </li></ul><ul><li>Normal concentration of PBI- 4-10µg/dl </li></ul><ul><li>0.1-0.2 µg/dl – T 3 , rest is T 4 . </li></ul>
  4. 6. Relation between T 4 and T 3 Thyroid secrets more T 4 than T 3 T 4 is major circulating hormone T 3 is 5 times more potent than T 4 and acts faster. T 3 is more avidly bound to the nuclear receptor than T 4 . About 1/3 of T 4 is converted to T 3 in peripheral tissues. On the basis of this ,it is believed that T 3 is the active hormone & T 4 is only the transport form.
  5. 7. <ul><li>THYROID STIMULATING HORMONE </li></ul><ul><li>It is 210 amino acid, two chain glycoprotein </li></ul><ul><li>MW 30000 </li></ul><ul><li>FUNCTIONS </li></ul><ul><li>Stimulates thyroid to synthesize and secrete thyroxin (T4) </li></ul><ul><li>& Triiodothyronin (T3) </li></ul><ul><li>Induces hyperplasia & hypertrophy of thyroid follicles </li></ul><ul><li>Promotes trapping of iodide by thyroid </li></ul><ul><li>Promotes organification of trapped iodine & its incorporation into </li></ul><ul><li>T3 & T4 By increasing Peroxidase activity </li></ul><ul><li>-Enhances endocytotic uptake of thyroid colloid by the follicular cells </li></ul><ul><li>-Proteolysis of thyroglobulin to release more T3 & T4. </li></ul>
  6. 8. Nuclear thyroid hormone receptor <ul><li>ACTIONS </li></ul><ul><li>Growth and development </li></ul><ul><li>Intermediary metabolism </li></ul><ul><li>Calorigenesis </li></ul><ul><li>CVS </li></ul><ul><li>Nervous system </li></ul><ul><li>Skeletal muscle </li></ul><ul><li>GIT </li></ul><ul><li>8) Kidney </li></ul>
  7. 9. <ul><li>Cretinism </li></ul><ul><li>Adult hypothyroidism </li></ul><ul><li>Myxoedema coma </li></ul><ul><li>Nontoxic goiter </li></ul><ul><li>Thyroid nodule </li></ul><ul><li>6. Papillary carcinoma of thyroid </li></ul>
  8. 10. Thyrotoxicosis -main causes Graves Disease Toxic nodular goiter <ul><li>Classification </li></ul><ul><li>Inhibit hormone synthesis(Antithyroid drugs) </li></ul><ul><li>Inhibit iodide trapping (ionic inhibitors) </li></ul><ul><li>Inhibit hormone release </li></ul><ul><li>4. Destroy thyroid tissue </li></ul>Propylthiouracil Methimazole Carbemazole Iodine Iodides of Na & K Organic iodide Thiocyanates(-SCN) Perchlorates (-ClO 4 ) Nitrates (-NO 3 ) Radioactive iodine ( 131 I, 125 I, 123 I)
  9. 11. Inhibits thyroid hormone release- Lithium Inhibit peripheral conversion of T4 to T3- Amiodarone Inhibit thyroglobulin iodination and coupling reaction- Sulphonamides Paraaminosalicylic acid Induce metabolic degradation of T4/T3- Phenobarbitone Phenytoin Carbamazepine Rifampin

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