UVB rays

Skin

7-dehydrocholesterol (precursor made in liver)

Vitamin D₃ (Cholecalciferol)

Diet and Supplements (fish, eggs, cheese, supplement bottle)

Liver (25-OHase) Converts Vitamin D₃ to 25-hydroxyvitamin D₃ (Calcidiol)

25-hydroxyvitamin D₃ (Calcidiol)

Renal production (Kidney) Produces 1,25-dihydroxyvitamin D₃ (active form)

Non-Renal production Also leads to 1,25-dihydroxyvitamin D₃

1,25-dihydroxyvitamin D₃ (active form)

Endocrine action

Pancreas ↑ insulin secretion

Bone bone metabolism & mineralization

Intestine ↑ calcium & phosphate absorption

Autocrine & paracrine action Effects on cell proliferation, differentiation, immune regulation