Active form of Vitamin -D ?

Ans. is 'c' i.e., 1,25-dihydroxycholecalciferolVitamin DVitamin D is the major vitamin involved in the absorption of calcium.Beside dietary intake, cutaneous synthesis is the other and more impoant source of vitamin D (cholecalciferol) in the body. The keratinocytes of stratum corneum of the epidermis of skin contain 7-dehydrocholesterol which is conveed to Vitamin D3 (cholecalciferol) by the action of sunlight (UV light).This vitamin D3 (Cholecalciferol) is conveed to calcidiol (calcifediol or 25 hydroxy cholecalciferol or 25hydroxy vitamin D3) by 25 hydroxylase in the livery.Calcidiol is the major circulating form of vitamin D3.Calcidiol is then conveed to Calcitriol (1-25 dihydroxy-cholecalciferol or 1-25 dihydroxy vitamin D3) by 1-a hydroxylation in kidneys.The final hydroxylation in kidney is rate limiting steps.Calcitriol is the active form of vitamin D.Dietary vitamin D is absorbed in ileum Q and requires bile salts.When Ca+2 level is high, little calcitriol is produced, and the kidney produce the relatively inactive metabolite 24, 25 dihydroxycholecalciferol insteadY.