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Bone 1000 g Ca++ stored in bone Calcium homeostasis Blood Ca++ small intestine kidney Ca++ lost in urine Calcium in the diet calcium lost in feces Ca++

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Presentation on theme: "Bone 1000 g Ca++ stored in bone Calcium homeostasis Blood Ca++ small intestine kidney Ca++ lost in urine Calcium in the diet calcium lost in feces Ca++"— Presentation transcript:

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

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

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 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 Cholesterol precursor7-dehydrocholesterol UV Vitamin D3 25 Vitamin D3 1,25 Vitamin D3 Low plasma Ca++ increase kidney enzymes

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


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