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Calcium homeostasis

kidney. bone. calcium deposition. calcium resorption. 1000 g Ca++ stored in bone. Ca++ absorbed into blood. Ca++ lost in urine. Calcium in the diet. calcium lost in feces. small intestine. Calcium homeostasis. Blood Ca++. storage. kidney. calcium deposition. calcium resorption.

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Calcium homeostasis

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  1. kidney bone calcium deposition calcium resorption 1000 g Ca++ stored in bone Ca++ absorbed into blood Ca++ lost in urine Calcium in the diet calcium lost in feces small intestine Calcium homeostasis Blood Ca++

  2. storage kidney calcium deposition calcium resorption intake Ca++ absorbed into blood Ca++ lost in urine excretion Calcium in the diet calcium lost in feces small intestine Calcium homeostasis bone Blood Ca++ 1000 g Ca++ stored in bone

  3. Calcium cycling in bone tissue • Bone formation • Osteoblasts • Synthesize a collagen matrix that holds Calcium Phospate in crystallized form • Once surrounded by bone, become osteocyte • Bone resorption • Osteoclasts • Change local pH, causing Ca++ and phosphate to dissolve from crystals into extracellular fluids

  4. kidney bone calcium deposition calcium resorption Ca++ absorbed into blood Ca++ lost in urine Calcium in the diet calcium lost in feces small intestine Calcium homeostasis Blood Ca++

  5. Hormonal Regulators • Calcitonin (CT) • Parathormone (PTH) • 1,25 Vitamin D3

  6. Calcitonin (CT) • Secreted from the C cells in the thyroid • Lowers Ca++ in blood • Promotes deposition of Ca++ into bone (inhibits osteoclasts) • Control of secretion from c-cells: CT

  7. Hormonal Regulators • Calcitonin (CT) • Lowers Ca++ in the blood • Inhibits osteoclasts • Parathormone (PTH) • 1,25 Vitamin D3

  8. Parathormone (PTH) • Increases Ca++ in blood • Increases Ca++ resorption from the bone • Stimulates osteoclasts • Increases number of osteoclasts • Increases Ca++ resorption from nephron • Control of secretion: • Necessary for fine control of Ca++ plasma levels

  9. Hormonal Regulators • Calcitonin (CT) • Lowers Ca++ in the blood • Inhibits osteoclasts • Parathormone (PTH) • Increases Ca++ in the blood • Stimulates osteoclasts • 1,25 Vitamin D3

  10. UV Cholesterol precursor 7-dehydrocholesterol Vitamin D3 25 Vitamin D3 1,25 Vitamin D3 Low plasma Ca++ increase kidney enzymes 1,25 Vitamin D3 • Increases Ca++ uptake from the gut • Increase transcription and translation of Ca++ transport proteins in gut epithelium • Minor roll: also stimulates osteoclasts • Increase Ca++ resorption from the bone

  11. Hormonal Regulators • Calcitonin (CT) • Lowers Ca++ in the blood • Inhibits osteoclasts • Parathormone (PTH) • Increases Ca++ in the blood • Stimulates osteoclasts • 1,25 Vitamin D3 • Increases Ca++ in the blood • Increase Ca++ uptake from the gut • Stimulates osteoclasts

  12. kidney bone 1,25 Vit. D3 (+) Parathormone (+) PTH Ca++ Ca++ 1,25 Vit D3 Ca++ Ca++ small intestine Calcium homeostasis Blood Ca++ Calcitonin (-) resorption deposition

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