The blood levels of 1,25 dihydroxycholecalciferol is positively regulated by:-
PTH - PTH is necessary for conversion of 25-hydroxy chole calciferol to 1,25 - dihydroxy cholecalciferol: Calcium: Plasma concentration of 1,25 ( OH)2 D3 is inversely affected by Ca2+ concentration in plasma. The rate of PTH secretion is greatly suppressed when plasma Ca2+ concentration rise above 9-10 mg/100gm If Ca2+ concentration below this level - | es conversion of 25 hydroxycholecalciferol to 1,25 dihydroxycholecalciferol in the kidney At higher calcium concentration when PTH is suppressed the 25 Hydroxycholecalciferol is conveed to a different component - 24, 25- Dihydroxy cholecalciferol & that has almost no vitamin D defect
PTH
Calcium
Magnesium
25 OH cholecalciferol
Endocrine System