<prompt> 1,25-dihydroxycholecalciferol is secreted by:Adrenal coexLiverProximal tubules of kidneyCollecting ducts of kidney  <response>: It is the most active form of vitamin D1,25-dihydroxycholecalciferol calcitriol When UV rays fall on the skin, 7-dehydrocholesterol in the skin is conveed into cholecalciferol. It goes to the liver, a hydroxyl group is attached to it, 25-OH cholecalciferol is formed. It then travels to kidneys. In the cells of the PCT, one more hydroxyl group is attached, to form the active metabolite 1,25-dihydroxycholecalciferol. Vit. D is considered a steroid hormone. It acts on the intestines, kidneys, and bone. Its chief function is to increase Ca2 and PO42- in the ECF. 