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Parathyroid Gland and Related Hormones

Parathyroid Gland and Related Hormones. Vitamin D and Calcitonin Prof. K. Sivapalan. Structure of Bone. Cells in Bone. Osteocytes- resting cells. Osteoblasts are active in bone formation Calcification occurs only in bone and not usually in tissues.

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Parathyroid Gland and Related Hormones

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  1. Parathyroid Gland and Related Hormones Vitamin D and Calcitonin Prof. K. Sivapalan

  2. Structure of Bone Parathyroid Gland and related hormones

  3. Cells in Bone • Osteocytes- resting cells. • Osteoblasts are active in bone formation • Calcification occurs only in bone and not usually in tissues. • Osteoclasts are responsible for removal of bone • Remodeling- continuous removal and formation. Parathyroid Gland and related hormones

  4. Bone structure . • Collagen fiber laid down by fibroblasts is the basic inter cellular substance. • Hydroxyappetite[Ca10(PO4)6(OH)2] crystals + other surface crystals, CaHPO4 are deposited on collagen by osteoblasts. • Osteocytes are arranged in Havesian system. • Stimuli of bone formation- • stress and strain. • growth factors and hormones. • (calcium and protein) Parathyroid Gland and related hormones

  5. Plasma Calcium. • Calcium phosphate readily ionizes and equilibrates with plasma. • Plasma calcium- • 50% bound to protein, • 5% complex with anions of plasma, • 45% ionized (active). Parathyroid Gland and related hormones

  6. Calcium Balance • Gain during growth. • Plateau- middle age. • Loss in old age - osteoporosis. Parathyroid Gland and related hormones

  7. Vitamin D. • Control of synthesis: • Feed back in kidney- higher plasma calcium inhibiting [production of inactive 24,25 dihydroxycholycalciferol] • Parathormaone stimulation production in kidney Parathyroid Gland and related hormones

  8. Actions of Vitamin D. • Increases absorption of Calcium in intestine and kidney [Calbindins in intestine, kidney etc]. • Increases osteoclasts in bone. • Increase plasma calcium. • Bone formation ? Indirect through plasma calcium levels. • Differentiation of immune cells and keratinocytes of skin. • Rickets is the result of deficiency in children. Low plasma calcium leads to non calcification of epyphysis with excess growth of cartilage and week bone. Adults- osteomalasia. Parathyroid Gland and related hormones

  9. CALCITONIN. • From para follicular cells of thyroid. • 32 amino acids, 3000 mw. • Effects- • Reduce osteiclastic activity • Increase osteoblastic activity. • Reduce formation of osteoblasts. • Control- calcium feedback. Parathyroid Gland and related hormones

  10. PARATHYROID HORMONE • gland- 4 lobs, behind thyroid. • 84AA, mw- 9500. • Half life- 20 min. Parathyroid Gland and related hormones

  11. Actions of Parathyroid Hormone • Maintenance of plasma calcium. • Bone- • increase osteoclastic activity. • reduces osteoblastic activity. • Kidney- • increase conversion of Vitamin D. • increase reabsorption of calcium • decrease re-absorption of phosphates. • Intestine- • increase calcium absorption- direct action is mild. Main action is through increased Vitamin D. Parathyroid Gland and related hormones

  12. Control of Secretion of Parathyroid Hormone. • Calcium negative feedback. • β adrenergic stimulation increases secretion. Parathyroid Gland and related hormones

  13. Hyper Parathyroidism • Causes- tumors. (in pregnancy and lactation hypertrophy is normal). • Effect- increased plasma calcium. • Bone- • increased osteoclastic activity. • easily broken bones, multiple fractures with mild trauma. • X ray- eaten up bone appearence. • increased alkaline phosphatase Parathyroid Gland and related hormones

  14. Hypoparathyroidism • Reduced plasma Calcium • Tetany. • Carpo-pedal spasm (Trousseau's sign) • Facial muscle twitch on tapping.- (Chvostek's sign) Parathyroid Gland and related hormones

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