Human skin serves which of the following functions?
- Innate immunity
- Production of the inactive form of vitamin D
- I only
- I and III only
- II and III only
- I, II, and III
This question asks the examinee to determine various functions performed by the human skin. Human skin has an acidic pH of approximately 5.5, which serves to protect the body from pathogens. The skin also synthesizes vitamin D, from cholesterol, in the presence of sunlight. This vitamin D synthesized in the skin is in its inactive form, cholecalciferol (the active form of vitamin D is calcitriol, which is produced from cholecalciferol in the kidneys). Thermoregulation is also a function of the skin. When the body overheats, the capillaries in the skin dilate to increase blood flow allowing for the dissipation of heat. When the body is cold, hair follicles in the skin contract, which serves to insulate the body and conserve heat. Therefore I, II, and III are all functions of skin in humans, making D the correct answer.
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