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THYROID GLAND

BIOCHEMISTRY

mprasadnaidu
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THYROID GLAND

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  1. THYROID GLAND M.Prasad Naidu MSc Medical Biochemistry, Ph.D,.

  2. Thyroid gland • Thyroid tissue is present in all vertebrates • TG consists of 2 lobes, one on each side of trachea • H- shape • 25 gms • Season, climate, geographical location, food

  3. Thyroid gland • Thyroglobulin : glyco protein – storage form of thyroid glands • TGb on hydrolysis – MIT & DIT • TGb on hydrolysis also yields non-iodinated compounds which ↓serum Ca2+

  4. Biosynthesis & secretion • Entry of iodide ions from the blood • Against the conc. Gradient (Active tpt) • ↑TSH • ↓Thiocyanate, perchlorate • Oxidation of I- to I+/ HIO- (iodide peroxidase) • Iodination first at 3rd & 5th • MIT • DIT • Synthesis of T2,T3 and T4

  5. Functions • T3 is the most reactive • 5-10 time more active than T4 • ↑ Protein synthesis • ↑ blood sugar ( Hyperglycemia) • ↑ utilization of glucose • ↑ glycolysis, TCA cycle, HMP shunt • ↑ lipolysis & lipogenesis • ↑ degradation of cholesterol – bile acids • ↑ rate of energy exchange & O2 consumption (calorigenic effect) • ↑ requirement of certain B complex vitamins • ↑normal growth & skeletal maturation • ↑ heart beat rate (T4) • Partly effects calcium levels

  6. Regulation • TSH • Growth of TG, iodide uptake, oxidation, iodination, coupling & release of thyroid hormones

  7. Clinical importance • T3 & T4 are synthesized only when sufficient iodine is supplied in the diet • Goiter – Iodine deficiency • hypothyroidism: • Myxedema in adults • Cretinism in children • Hyper thyroidism: Graves disease

  8. Parathyroid gland • In humans , usually 4 • 2 are superior poles & 2 are in inferior poles of thyroid gland • 4 glands weigh about 0.3gm • 2 hormones namely • Parathormone (PTH) • Calcitonin

  9. PTH • Linear PP • 84 aa • 8500 • N- Ala & C- glutamine • Chief cells of parathyroid glands

  10. functions • ↑ Ca conc in serum by • i) ↑ absorption of Ca from the intestine • ii) ↑ rate of mobilization of Ca from bones • iii) ↑ renal tubular reabsorption • Thus PTH produces Hypercalcimia • ↓ P conc in serum • ↑ elimination of Ca & P in urine • ↑ citrate content of blood, kidney & bones • ↑ alkaline phospatase & acidphosphatase in blood plasma • Depolymerization of skeletal mucopolysaccharides • Acts on kidney through ↑ cAMP

  11. Regulation • PTH is not stored in the gland • Synthesized & secreted continuously • PTH requires Vit D for its functioning • When Ca conc is low , PTH secretion is ↑

  12. Calcitonin • Thyroid and parathyroids • Synthesized from C-cells or parafollicular cells • Single PP • 32 aa • 3600 • N- Cys & C- prolinamide

  13. Functions • Causes rapid & brief ↓ Ca level in blood • Influences the tpt of ions in the kidney • Regulation: • Blood Ca levels • ↑ in serum Ca ↑ calcitonin - hypocalcimia

  14. THANK YOU

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