c. Heat Distributed by the Blood. Blood flow plays a role in the regulation of
normal body temperature because blood contains a large volume of water (an excellent
heat absorber and coolant).
a. Respiratory System/Skin. When the body becomes warm--hot summer
weather, strenuous exercise, and so forth--, blood temperature becomes higher and activates
the heat losing center (the hypothalamus). Impulses are sent to the sweat glands of the
skin, and these sweat glands produce perspiration. Perspiration evaporates from the
surface of the skin, and the skin is cooled. About 80 to 95 percent of body heat is lost
through the skin.
b. Urine/Feces. Two ways in which the body maintains its almost constant
normal temperature are through urination and elimination of feces.
EXCESSIVE HEAT LOSS
The goal of the hypothalamic thermostat in the body is to maintain a constant
body temperature. If your heat-losing mechanisms give off more heat than your heat-
producing mechanisms, then your temperature falls. An artificial way to prevent too
much heat loss is by wearing appropriate clothing. Clothing which is slightly loose
creates a dead space which insulates the body. A natural means of preventing too
much heat loss is the body's subcutaneous fat. Body fat conducts heat only one-fourth
as rapidly as other tissues, thus conserving heat.
BODY TEMPERATURE REGULATION MECHANISM
a. Hypothalamus. The hypothalamus is a small portion of the brain which
controls many body activities, some of which are related to homeostasis (the condition
in which the body's temperature remains about the same most of the time). The
hypothalamus has two main centers: a center which controls heat production and a
center which controls heat loss.
(1) Control of body heat production. When the body is exposed to internal
or external temperatures above normal, the blood vessels expand. There is increased
sweating and panting, and the body produces less heat.
(2) Control of body heat loss. If the body is exposed to low temperatures,
the blood vessels shrink, the surface hair on the skin stands erect, and the person
shivers. All of these responses slow down the loss of body heat.
b. Body Reactions.