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

2. Parathyroid Gland and related hormones
Structure of Bone
Parathyroid Gland and related hormones

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

7. Parathyroid Gland and related hormones
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. Parathyroid Gland and related hormones
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. Parathyroid Gland and related hormones
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 Gland and related hormones
PARATHYROID HORMONE
gland- 4 lobs, behind thyroid.
84AA, mw
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. Parathyroid Gland and related hormones
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. Parathyroid Gland and related hormones
Hypoparathyroidism
Reduced plasma Calcium
Tetany.
Carpo-pedal spasm (Trousseau's sign)
Facial muscle twitch on tapping.- (Chvostek's sign)
Parathyroid Gland and related hormones