Thermoregulation in skin during exercise

Steps:

• During a long run, the body generates excess heat from muscle activity.
• To dissipate heat, skin blood vessels dilate (vasodilation) to increase blood flow and heat loss.
• Sweat glands activate to produce sweat, which evaporates and cools the skin.
• These responses maintain core body temperature.

Why D is correct:

• Vasodilation widens skin blood vessels and sweating increases to enhance evaporative and radiative cooling, per the body's thermoregulatory mechanism.

Why the others are wrong:

• A: Vasodilation occurs, not constriction; sweating increases for cooling.
• B: Sweating increases, not decreases, to aid heat loss.
• C: Both vasodilation and sweating increase, not decrease.

Final answer: D