What occurs during vasoconstriction in response to cold?

• A. Blood vessels narrow to keep heat near essential organs.
• B. Blood vessels widen to release heat.
• C. Blood flow to skin increases.
• D. The acid mantle becomes more acidic.

Answer: (A)

When it’s cold, the body uses vasoconstriction to conserve heat. The hypothalamus triggers the sympathetic nerves, causing the smooth muscle in skin arterioles to contract. This narrows the vessels, especially near the surface, so less warm blood flows to the skin and more stays in the core. The result is reduced heat loss to the surroundings, helping to keep essential organs warm. This is why keeping heat near vital areas is the intended response. The other options describe responses to heat (vasodilation to release heat or increased skin blood flow to the skin) or unrelated changes, which don’t fit cold-induced temperature regulation.