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PTH Calcitonin 10mg% Vitamin D Lecture 52 Ca++ Homeostasis

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Presentation on theme: "PTH Calcitonin 10mg% Vitamin D Lecture 52 Ca++ Homeostasis"— Presentation transcript:

1 PTH Calcitonin 10mg% Vitamin D Lecture 52 Ca++ Homeostasis
Effect on serum calcium PTH Calcitonin mg% Vitamin D Normal serum calcium

2 Dietary Ca++ Ca++ ECF Ca++ Bone Intestine Ca++ Kidney

3 PTH Chief cells of Parathyroid gland 84 a.a- 9,500 MW
1st Biological Activity Transcription Translation Pre Pro PTH Pro PTH PTH PTH Serum Ca++

4 Mode of Action of PTH Bone Kidney Osteoclast number
Receptor for PTH on osteoblasts Secrete Factors Osteoclast differentiating Factor PTH (RANKL) Stimulate Osteoclasts (In the presence of preosteoclasts) osteoblasts Kidney Inhibits phosphate reabsorption (Proximal and distal tubule). Stimulates Calcium reabsorption (distal).

5 Parathyroid hormone gene related peptide
PTHrP Isolated from Lung tumors Kidney tumors Responsible for the hypercalcemia of malignancy

6 Calcitonin Main effect on Bone Osteoclasts shrink in size 32 aa
3,000 mw C cells of thyroid. Main effect on Bone Inhibits osteoclastic bone resorption Osteoclasts shrink in size

7 Vitamin D Metabolism * 24(OH)ase 24,25(OH)2D3 (inactive metabolite)

8 Mechanisms of Action of Steroids

9 1,25(OH)2D3 Intestine calcium binding protein calbindin
epithelial calcium channel TRPV6 intestinal calcium absorption (also phosphate absorption) Bone stimulates osteoclastic activity intracellular receptor for 1,25(OH)2D3 in osteoblasts 1,25(OH)2D3 stimulates synthesis of RANKL Stimulates osteoclasts (in the presence of preosteoclasts Kidney enhances the action of PTH at the distal tubule

10 Summary BONE KIDNEY INTESTINE PTH Calcitonin Vitamin D #osteoclasts
Inhibits phosphate reabsorption (proximal and distal tubule) Increases calcium reabsorption (distal tubule) No direct effect PTH 1,25(OH)2D3 which calcium absorption (intestine) Calcitonin SHRINKS osteoclasts Urinary calcium excretion (only at supra-physiological concentration) No effect (inhibits gastric secretion from stomach) Vitamin D Calcium absorption #osteoclasts Enhances action of PTH on calcium at the distal tubule (also phosphate absorption)


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