The synthesis of calcitriol, a steroid hormone secreted by the kidney, is dependent on the availability of a related steroid called cholecalciferol (vitamin D3), which may be synthesized in the skin or absorbed from the diet. a. True
b. False

True.

Explanation:

Vitamin D is a fat soluble vitamin that is responsible for fostering the absorption of calcium, magnesium and phosphate in the body.

The synthesis of calciferol is dependent on the availability of a related steroid called cholecalciferol (vitamin D3), which may be synthesized in the skin or absorbed from the diet because keratinocytes of the epidermis and fibroblasts of the skin is response for producing vitamin D3(calciferol) by absorbing it from ultraviolet light when during exposure to UV B photons which protolyses provitamin D3 to pre vitamin D3 in the human body.

It can also be gotten from food sources like milk, cheese, cereals, liver,meat e.t.c.

a symbiotic relationship with the mitochondria