Bone Mineral Homeostasis
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Bone mineral homeostasis
Mr. Ujjal Bose
Lecturer
KMCIC
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Calcium : 1-2kg
Phosphate: 1kg
Calcium: plasma Ca is regulated by PTH, Vit D,& calcitonin
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Uses: tetanyOsteoporosisDietary supplementParathyroid hormone:Secretion regulated by plasma Ca levelsRegulates Ca and phosphate influx across cellular
membranes in bone & kidneyActions:Bone: increases bone resorption by increasing the no. &
activity of osteoclastsKidney: increases the reabsortion of Ca & reduces that of
phosphateStimulates the production of 1,25-dihydroxyvitamin DIntestines: indirectly increases absorption of caTeriparatide: recombinant PTH
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Clinical features of acute Hypoparathyroidism
• Hypocalcemia• Tetany• Carpopedal spasm• Laryngospasm• Tingling of lips, hands, muscles• Convulsions
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Clinical features of chronic Hypoparathyroidism
• Loss of hair
• Brittle finger nails
• Caries teeth
• Cataract
• Anxiety & Depression
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Vitamin DD3 - cholecalciferolD2 – ergocalciferaolActivation of Vit D: hydroxylated in the liver to 25-
hydroxyvitamin D → 1,25-dihydroxyvitamin D (calcitriol)Actions:Intestine: increases the absorption of Ca and PO4 Bone: increases Ca & PO4 resorptionKidney: excretion of Ca & PO4 is decreased
• •
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Preparations of Vitamin D • Ergocalciferol (Vit. D2):Oral capsules- 400 IU/day
for prevention of rickets in children and osteomalacia in adults.
• Cholecalciferol (Vit D3): oral and IM injection
Prodrugs, orally effective and are rapidly biotransformed into calcitriol in the liver.
They are effective in renal bone disease and hypoparathyroidism
• Calcitriol: oral capsules and solution Alfacalcidol
Dihydrotachysterol• Calcipotriol: Vit D analogue used topically in
psoriasis.
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Uses: Prophylaxis & treatment of Vit D deficiencyRickets:Vit D resistant ricketsVit D dependent ricketsRenal ricketshypoparathyroidism
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Calcitonin: Secreted by parafollicular ‘C’ cells of thyroid Regulated by plasma Ca levelsActions:bone: inhibits osteoclastic bone resorptionKidney: Inhibits reabsortion of Ca & PO4
Bisphosphonates: etidronate, pamidronate, alendronate, risendronate
Mechanism: retard formation and dissolution of hydroxyapatite crystals
Localize to regions of osteoclastsblock farnesyl pyroposphateUse: osteoporosis Paget’s diseaseHypercalcemia of malignancyOsteoclastic bone metastasis
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Adverse effects: gastric irritationCalcimimetics: Cinacalcet: activates calcium sensing
receptor on parathyroid glandBlocks PTH secretionUse: secondary hyperparathyroidism in
chronic kidney diseaseParathyroid carcinomaPlicamycin: cytotoxic antibioticUse: hypercalcemiaPaget’s disease