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Essentials of Clinical Nephrology (Shorouk Press, Cairo, 2000, ISBN ...

Essentials of Clinical Nephrology (Shorouk Press, Cairo, 2000, ISBN ...

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7-Dehydroxycholesterol<br />

UV light<br />

on skin<br />

Diet<br />

Cholecalciferol<br />

(vitamin D3)<br />

Liver<br />

25-Hydroxycholecalciferol (activity =1)<br />

Hypophosphataemia<br />

Kidney<br />

Parathormone<br />

1,25- Dihydroxycholecalciferol (activity =100)<br />

(1,25-DHCC)<br />

Gastrointestinal<br />

calcium<br />

absorption<br />

Formation <strong>of</strong><br />

bone<br />

(anti-rachitic)<br />

(Fig. 1.2)<br />

Activation <strong>of</strong> Vitamin D<br />

Parathormone and hypophosphataemia are the main stimuli for<br />

renal production <strong>of</strong> 1,25- (OH)2 vit.D.<br />

The exact site <strong>of</strong> synthesis is unknown, although the 1-hydroxylase<br />

enzyme is found in proximal tubular cells.<br />

The major effects <strong>of</strong> vitamin D are to increase gastrointestinal<br />

calcium absorption and to promote normal bone calcification. Also<br />

vitamin D and its metabolites have important effects on skeletal<br />

muscle strength.

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