Which statement about vasodilation is true?

• A. Widening of blood vessels to release heat
• B. Narrowing of blood vessels
• C. Decreased sweat production
• D. Increased hair growth

Answer: (A)

Vasodilation is the widening of blood vessels, especially those near the skin, which increases blood flow to the surface. When the body needs to cool down, the smooth muscle in these vessels relaxes, making the diameter larger. More blood reaching the skin helps transfer heat from the core to the exterior, where it can be lost to the environment. Sweating may also help with cooling, but vasodilation itself is specifically about increasing vessel size and blood flow. The other statements describe narrowing of vessels (vasoconstriction), or are unrelated to this mechanism, such as decreased sweat production or increased hair growth.