vitamin D
cholecalciferol = D3
1α,25-dihydroxycholecalciferol = metabolically active form
Net effect: ↑ plasma calcium, ↑ PO4
Unlike PTH, vitamin D also ↑ plasma PO4 while PTH acts to lower it
| Site | Action |
|---|---|
| Intestine | Increases calcium and phosphate absorption in the ileum |
| Kidney | Increases reabsorption of calcium at thick ascending limb/distal tubule via activation of basolateral Ca2+ ATPase Increases renal tubular reabsorption of phosphate |
| Bone | Stimulates release of calcium from bone (Indirectly activates osteoclasts via stimulation of osteoblasts to release RANKL) |
| Parathyroid gland | Inhibits PTH secretion |
Stimulation:
Inhibition:
- hypercalcaemia (indirectly - by ↓PTH)