Question

Calcitriol is the ________.

1) precursor to vitamin D that is activated by sunlight
2) plant source of vitamin D
3) animal food source of vitamin D
4) biologically active form of vitamin D

Answer 1

Calcitriol is the biologically active form of vitamin D, produced in the kidney from calcitiriol, and is essential for calcium absorption and bone health.

Step-by-step explanation:

Calcitriol is the biologically active form of vitamin D. In the skin, cholesterol is converted to cholecalciferol (vitamin D3) under the influence of UV radiation. This form is then converted in the liver to calcidiol (25(OH)D), which circulates in the blood. Finally, in the kidney, calcidiol undergoes another conversion to calcitriol, the active form of vitamin D known as 1,25-dihydroxycholecalciferol. This form of vitamin D is necessary for the absorption of calcium in the digestive tract, its reabsorption in the kidneys, and the maintenance of normal serum concentrations of calcium and phosphate, which are vital for bone health and other physiological functions.