Questions: Which of the following is a metabolic function of skin? elimination of nitrogenous wastes cutaneous sensation body temperature regulation synthesis of a vitamin D precursor

The answer is the fourth one: synthesis of a vitamin D precursor.

Explanation for each option:

1. Elimination of nitrogenous wastes: This is primarily a function of the kidneys, not the skin. The skin does excrete some waste products through sweat, but this is not its primary metabolic function.

2. Cutaneous sensation: This refers to the skin's ability to sense touch, pressure, pain, and temperature. While it is an important function of the skin, it is not a metabolic function.

3. Body temperature regulation: The skin plays a crucial role in regulating body temperature through processes such as sweating and vasodilation/vasoconstriction. However, this is more of a physiological function rather than a metabolic one.

4. Synthesis of a vitamin D precursor: The skin synthesizes a precursor to vitamin D (cholecalciferol) when exposed to UV radiation from sunlight. This is a metabolic function because it involves the conversion of a substance into another form that the body can use.

Summary: The metabolic function of the skin among the given options is the synthesis of a vitamin D precursor.