When it is cold the blood vessels of the skin ____________
A. dilate to increase blood flow to the skin B. constrict to reduce the amount of flow of blood C. dilate to reduce the amount of blood flowing to the skin D. constrict to increase the amount of blood flowing to the skin
Correct Answer: B
Explanation
When it is cold, the capillaries near the skin surface constrict while those in deep layers dilate. This causes a smaller volume of blood to flow near the surface of the skin so that heat loss is reduced greatly. This conserves body heat. When it is hot, the capillaries near the skin surface dilate, while those in the deeper layers of the skin constrict. This causes a larger volume of blood to flow near the surface of the skin so that heat is lost to the surroundings via conduction, convection and radiation.
