Topic 13-Calcium-S_2011

Topic 13-Calcium-S_2011 - 13. Calcium homeostasis Click...

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Click to edit Master subtitle style 13. Calcium homeostasis A. Calcium & phosphate balance B. Hormones 1) PTH 2) Vitamin D 3) Calcitonin C. How the 3 interact to control calcium D. Osteoporosis
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Consider n Mineral content is hydroxylapatite Ca10(PO4)6(OH) 2 n Not a static tissue ¨ Growth ¨ Healing ¨ Remodeling: the 22 Major reservoir of Ca2+ & PO42
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Bone is a dynamic n Osteocytes ¨ 90% of total ¨ Exist in collagen matrix n Osteo b lasts & Bone formation ( b uild) n Osteoclasts & Reabsorption n OBs ± OCs 33 n >1,000,000 sites in skeleton Osteocytes Ca 2+ PO 42− Ca 2+ PO 42− Ca 2+ PO 42− Ca 2+ PO 42− Formation Formation Reabsor ption
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44 n ECF [Ca2+] must be maintained ¨ 2.1-2.6 mM total [Ca2+] ¨ ~50% bound to protein n Internal Ca2+ tightly regulated n Many proteins are present to ensure this Calcium is the critical second Calcium signaling requires precise gradients be maintained across internal and external cellular membranes Ca 2+ Ca 2+ AT P AT P Ca 2+ N a + Ca 2+ 2.3 mM [Ca2+]o ~10 >100 μM
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Calcium distribution & 66 Feces 825 mg 1000 mg Diet Extracellular Fluid (1000 mg) Kidneys Urine 175 mg 500 mg 325 mg 9825 mg 10,000 mg B o n e 280 mg 280 mg 99.99% of Ca2+ is in bone Bone is balanced Gut
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Phosphate provides balance to 77 Feces 500 mg 1400 mg Diet Extracellular Fluid (600 mg) Kidneys Urine 900 mg 1100 mg 200 mg 6100 mg 7000 mg 210 mg 210 mg Soft tissues 100,000 mg Gut
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Bone ECF Ca2+ & PO42− are reciprocally n HA insoluble ¨ Good for bone ¨ Bad for ECF n Ca2+ equilibrium between bone & ECF is critical n PO42− must be excreted to mobilize bone Ca2+ 88 To ↑ Ca2+ in ECF Ca 2+ To ↓ Ca2+ in ECF PO 42 P O Bone Kidneys
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99 Regulation of plasma [Ca2+] n Equilibrium among ¨ Bone (remodeling) ¨ Digestive system (intake/elimination) ¨ Kidney (secretion/reabsorption) n Key points: ¨ Most calcium is present in bones ¨ Bone is a dynamic tissue under endocrine control
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10 10 Maintenance of Ca2+ n Parathyroid Hormone (PTH) n Calcitrol qactive form of Vitamin D n
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This note was uploaded on 02/22/2011 for the course PGY 452 taught by Professor Dr.baizer during the Spring '11 term at SUNY Buffalo.

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Topic 13-Calcium-S_2011 - 13. Calcium homeostasis Click...

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