PADI Divemaster Certification Practice Exam

When a diver experiences excessive heat, the body's physiological response is to dilate skin capillaries. This process, known as vasodilation, increases blood flow to the skin, allowing for more heat to be dissipated into the environment. By expanding the capillaries near the surface of the skin, the body effectively maximizes the surface area available for heat loss, helping to cool the internal temperature.

This response is especially critical during activities in warm water, where the risk of overheating can be significant. The increased circulation to the skin also facilitates perspiration, which is another cooling mechanism, as sweat evaporates and carries heat away from the body.

In contrast, the other options do not accurately describe the body's response to excessive heat. For instance, an increased heart rate might occur for various reasons but is not a primary response to overheating. Reduced skin circulation would hinder the body's ability to cool down, while a decrease in perspiration would also be counterproductive during heat stress. Therefore, dilation of skin capillaries is the correct answer, as it aligns with the body's natural efforts to regulate temperature through increased blood flow and enhanced heat loss.