When the body is hot, what happens to capillaries?

• A. Vasoconstriction
• B. Vasodilation
• C. No change
• D. Plateaus

Answer: (B)

When the body is hot, the vessels near the skin expand to promote heat loss. This vasodilation of the cutaneous capillaries increases blood flow to the skin, bringing more warm blood to the surface so heat can be transferred to the environment by radiation, convection, and evaporation (sweating). If the vessels tightened (vasoconstriction), heat loss would be reduced; no change would not help dissipate heat, and “plateaus” isn’t a vascular response.