Temperature, Body. Body temperature is a measurement of the heat in an animal’s body. The body of an animal generates heat by burning food. However, the animal also loses heat to–or gains heat from–its environment.
Birds and mammals, including human beings, are warm-blooded animals. Their body temperature almost always stays fairly constant, regardless of the temperature of their environment. The body of a warm-blooded animal balances the amount of heat it exchanges with the environment with the amount it produces by burning food. Nearly all other animals are cold-blooded animals. Their body cannot balance this heat exchange so accurately. As a result, their body temperature tends to vary with the temperature of their environment.
When taken orally, the average body temperature of a healthy, resting adult human being is 98.6 °F (37.0 °C). Physicians consider a temperature within 1 °F (0.5 °C) of this figure normal. A higher temperature may indicate a fever (see Fever ). A lower temperature may be a sign of old age or of certain illnesses.
Warm-blooded animals
make various physical and behavioral adjustments to regulate their heat exchange with the environment. In cold surroundings, they increase the production of body heat and decrease the amount of heat lost to the environment. In hot surroundings, they do just the opposite. A part of the brain called the hypothalamus controls these adjustments. Certain nerves in the skin and deep within the body send messages to the hypothalamus. The hypothalamus compares the temperatures of these areas with that of the brain. It triggers the necessary responses by nerves and glands to keep a normal body temperature.
Even with the various controls, the body temperature of a warm-blooded animal does not remain entirely constant. It changes slightly throughout the day. In a healthy human being, for example, the body temperature is lowest in the morning and then rises until late afternoon. It falls again during sleep. Strenuous activity can raise the body temperature. In cold surroundings, the temperature of the skin and limbs may drop far below the temperature deep within the body.
Each species of warm-blooded animal has its own normal body temperature. Each species also functions best when the temperature of its surroundings remains within a certain range. This range varies greatly from species to species, depending on such factors as the thickness of fur and the rate at which its body burns food. Some warm-blooded animals hibernate. During hibernation, their body temperature drops below normal. In fact, the body temperature of most hibernators drops almost to the temperature of their environment. See Hibernation .
Cold-blooded animals
lack the precise temperature regulation abilities that characterize warm-blooded creatures. However, many cold-blooded animals can exercise some physical and behavioral control over body temperature. Reptiles, for example, can alter the amount of heat their body absorbs from the sun by changing their skin color. Moreover, many reptiles alternately warm themselves in the sun and cool themselves in the shade, thereby maintaining a fairly constant body temperature throughout the day.
