Section VII. TEMPERATURE CONTROL BY MEANS OF THE BLOOD
10-38. ELIMINATION OF EXCESS HEAT
Heat is produced as a by-product by various activities of the human body,
particularly muscular contractions. When excess heat is accumulated, it must be
eliminated from the body to maintain a healthy condition.
a. The water of the blood has a great heat-carrying capacity.
b. There are superficial capillary beds in the subcutaneous layer, close to the
surface of the body. When the blood flows through these beds, some of its heat can
radiate directly to the surrounding environment.
c. The sweat glands take water from the blood and secrete it onto the surface
of the skin. Here, even more calories of heat are lost during the evaporation of the
10-39. CONSERVATION OF BODY HEAT
On the other hand, if the body has an insufficient amount of heat, heat loss must
be reduced. For this purpose, the superficial capillary beds can be closed down. Then,
the fat in the subcutaneous layer serves as insulation.
10-40. CORE TEMPERATURE CONTROL
Unlike the peripheral portions of the body, whose temperatures may vary
considerably, the center of the body must be maintained at a certain temperature within
very narrow limits.
a. Control. There are special temperature detectors in the hypothalamus of
the forebrainstem. These continuously monitor the temperature of the blood flowing
through the brain.
b. Counter-Current Mechanism. The peripheral blood in the limbs is several
degrees cooler than the blood in the center of the body. Therefore, it must be warmed
as it returns toward the heart. As previously described, the arteries and veins of the
limbs are located side by side as they extend from the trunk and through the length of
the limbs. As it returns to the trunk, cool venous blood is gradually warmed by the
arterial blood flowing in the opposite direction.