Lecture 52 Ca ++ Homeostasis PTH Calcitonin 10mg% Vitamin D Normal serum calcium Effect on serum...
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Transcript of Lecture 52 Ca ++ Homeostasis PTH Calcitonin 10mg% Vitamin D Normal serum calcium Effect on serum...
Lecture 52Ca++ Homeostasis
PTH
Calcitonin 10mg%
Vitamin D
Normal serum calcium
Effect on serum calcium
Dietary Ca++
Ca++
ECF
Ca++
Ca++
Intestine
Kidney
Bone
Ca++
Ca++
PTHChief cells of Parathyroid gland84 a.a- 9,500 MW1st 34 Biological Activity
Transcription
Translation
Pre Pro PTH Pro PTH PTH
6 10Serum Ca++
PTH
Mode of Action of PTH
BoneOsteoclast number
Receptor for PTH on osteoblasts
PTH
Secrete FactorsOsteoclast differentiating Factor
Stimulate Osteoclasts
Kidney•Inhibits phosphate reabsorption (Proximal and distal tubule).•Stimulates Calcium reabsorption (distal).
osteoblasts(In the presence of preosteoclasts)
(RANKL)
Parathyroid hormone gene related peptide
PTHrP
Isolated from
Lung tumorsKidney tumors
Responsible for the hypercalcemia of malignancy
Calcitonin
32 aa3,000 mwC cells of thyroid.
Main effect onBone
Inhibits osteoclastic bone resorption
Osteoclasts shrink in size
Vitamin D Metabolism
24,25(OH)2D3
(inactivemetabolite)
24(OH)ase *
Mechanisms of Action of Steroids
1,25(OH)2D3
Intestine calcium binding proteincalbindinepithelial calcium channel TRPV6intestinal calcium absorption(also phosphate absorption)
Bone stimulates osteoclastic activityintracellular 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
(also phosphate absorption)
Urinary calcium excretion (only at supra-physiological concentration)
Summary
BONE KIDNEY INTESTINE
PTH #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 SHRINKSosteoclasts
No effect (inhibits gastric secretion from stomach)
Vitamin D #osteoclasts Enhances action of PTH on calcium at the distal tubule
Calcium absorption