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Thyroid hormone
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  • 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.
  • 3.
    • Iodine uptake
    • 2. Oxidation and Iodination
    • Coupling
    • Storage and release
    • 5. Peripheral conversion of T 4 to T 3
  • 4.  
  • 5.
    • Plasma protein bound- 0.03-0.08 % T 4
    • 0.2-0.5% T 3
    • Binding occurs to 3 plasma proteins
    • Thyroxine binding globulin (TGB)
    • Thyroxine binding prealbumin (transthyretin)
    • Albumin
    • Normal concentration of PBI- 4-10µg/dl
    • 0.1-0.2 µg/dl – T 3 , rest is T 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.
  • 7.
    • THYROID STIMULATING HORMONE
    • It is 210 amino acid, two chain glycoprotein
    • MW 30000
    • FUNCTIONS
    • Stimulates thyroid to synthesize and secrete thyroxin (T4)
    • & Triiodothyronin (T3)
    • Induces hyperplasia & hypertrophy of thyroid follicles
    • Promotes trapping of iodide by thyroid
    • Promotes organification of trapped iodine & its incorporation into
    • T3 & T4 By increasing Peroxidase activity
    • -Enhances endocytotic uptake of thyroid colloid by the follicular cells
    • -Proteolysis of thyroglobulin to release more T3 & T4.
  • 8. Nuclear thyroid hormone receptor
    • ACTIONS
    • Growth and development
    • Intermediary metabolism
    • Calorigenesis
    • CVS
    • Nervous system
    • Skeletal muscle
    • GIT
    • 8) Kidney
  • 9.
    • Cretinism
    • Adult hypothyroidism
    • Myxoedema coma
    • Nontoxic goiter
    • Thyroid nodule
    • 6. Papillary carcinoma of thyroid
  • 10. Thyrotoxicosis -main causes Graves Disease Toxic nodular goiter
    • Classification
    • Inhibit hormone synthesis(Antithyroid drugs)
    • Inhibit iodide trapping (ionic inhibitors)
    • Inhibit hormone release
    • 4. Destroy thyroid tissue
    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)
  • 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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