Calcium
Source
- ingested in diet
- absorbed in small intestine / duodenum
- under control of vitamin D
Excretion
- through kidney
- majority is reabsorbed
- under control of vitamin D
Storage
- 99% stored in bone
PTH
Source
- produced by parathyroid glands
- in response to hypocalcaemia
Action
1. Vitamin D
- stimulates activation of Vit D in kidney
- vit D then increases absorption / decreases excretion / increases release from bone
2. Bone
- stimulates release of calcium from bone by indirect inhibition osteoclasts
3. Kidney
- increases resorption of calcium
- increases excretion of phosphate
Vitamin D
Generation of Vit D
Vitamin D3 ingested and absorbed
- activated by sunlight
- need 10 - 15 minutes 3 x per week
25 hydroxylated in liver
1 alpha-hydroxylase in kidney
- active 1,25 vit D3
- calcitriol
- this is under PTH control
Action Vit D
1. Intestine
- increases Ca and PO4 absorption
2. Kidney
- decreases Ca and PO4 excretion
3. Bone
- increases Ca and PO4 release