Where in the Body Does the Production of Precursors for the Synthesis

Question

Where in the body does the production of precursors for the synthesis of calcitriol occur?
A) bone
B) kidneys
C) small intestine
D) liver
E) skin

Accepted Answer

The production of precursors for the synthesis of calcitriol occurs in the skin when it is exposed to UVB radiation from sunlight. UVB radiation causes the conversion of 7-dehydrocholesterol in the skin to previtamin D3, which is then rapidly converted to vitamin D3. Vitamin D3 is then transported to the liver and kidneys where it is further processed into its active form, calcitriol.