The skin becomes pale and cold. Sometimes it takes on a bluish color, the result of a color change in the blood, which occurs when the blood, flowing slowly, gives off more of its oxygen than usual. Another signal from the brain stimulates muscular activity, which releases heat. Shivering is a form of this activity-a muscular reflex that produces heat. When the outside temperature goes up, the body's cooling system is ordered into action.
Sweat is released from sweat glands beneath the skin, and as it evaporates, the skin is cooled.
Heat is also eliminated by the evaporation of moisture in the lungs. This process is accelerated by panting. An important regulator of body heat is the peripheral capillary system. The vessels of this system form a network just under the skin. When these vessels dilate, they allow more warm blood from the interior of the body to flow through them, where it is cooled by the surrounding air.