How is vitamin D synthesized and regulated in the human body. Include any organ systems involved, hormones, and precursors
Synthesis of vitamin D starts from 7-dehydrocholesterol, which is photolyzed by exposure to sun. the product so formed isomerizes to form cholecalciferol, known as vitamin D3. Mostly the photochemical reaction occurs in the skin of animals. Vitamin D3 is then carried in blood to liver, for its hydroxylation to calcifediol (25-hydroxycholecalciferol). This is facilitated by enzyme vitamin D 25-hydroxylase. Calcifediol is hydroxylated to calcitriol (1,25-dihydroxycholecalciferol), the biologically active form of vitamin D. This is done by enzyme 25-hydroxyvitamin D3 1-alpha-hydroxylase. This enzyme is stimulated by release of parathyroid hormone (regulates calcium levels).
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