Calcium metabolism handout

7,083 views

Published on

0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
7,083
On SlideShare
0
From Embeds
0
Number of Embeds
41
Actions
Shares
0
Downloads
200
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

Calcium metabolism handout

  1. 1. 7-dehydrocholesterol Previtamin D3 Solar UVB radiation Skin Vitamin D3 Diet 25-hydroxylase 25(OH)-D 1-OHase 1,25(OH)2-D PTH effects on the kidney 1.Stimulates 1-OHase. 2.Decreases PO4 resorption in proximal tubule via increase in intracellular (and urinary) cAMP. 3.Increases Ca resorption in distal tubule. 1,25(OH)2-D effects on kidney Increases Ca resorption in distal tubule, by upregulating calbindin. 1α-hydroxylation Stimulated by Inhibited by PTH 1,25(OH)2-D Low PO4 High PO4 Possibly GH and insulin Extra-renal 1α-hydroxylation in macrophages, e.g. in sarcoidosis. Dietary Vit D Average daily intake 500 iU. Recommended intake 400 iU. 25(OH)-D 25-hydroxylase activity is essentially unregulated. 25(OH)-D is the major circulating metabolite, acting as a store. PTH effects on bone Acts on osteoblast cell membrane to increase permeability to calcium, activating a pump which drives calcium into ECF PTH production Main stimulus is low Ca2+. Inhibited by 1,25(OH)2-D. Mg required for synthesis, release and action of PTH. Response to hypocalcaemia Rise in PTH, causing: • increased renal Ca absorption; • increased renal PO4 excretion; • mobilization of calcium and PO4 from bone; • increased 1α-hydroxylation, causing: • increased GI absorption of calcium and PO4. Response to hypophosphataemia Stimulates 1α-hydroxylation, causing: • increased GI absorption of PO4 and calcium; • rise in calcium inhibits PTH release, causing: • increased renal PO4 resorption; • reduced renal calcium resorption. Vitamin D replacement Ergocalciferol = Vit D2 Cholecalciferol = Vit D3 Alfacalcidol = 1α(OH)-D3 Calcitriol = 1,25(OH)-D3 Calcitonin production Main stimulus is high Ca2+ (ionized>1.15) – also glucagon, gastrin, ß-adrenergic agonists (? reason for low Ca in acute illness) Calcitonin effects on bone • inhibits osteoclast resorption • thereby lowers Ca and PO4 • no effect on Mg 1,25(OH)2-D effects on gut Increases Ca2+ and PO4 absorption by upregulating intracellular calbindin proteins. Vit D effects on bone? Unsure if direct effect Calcitonin Parathyroid hormone

×