body temperature

temperature, body:

see body temperaturebody temperature,
internal temperature of a living organism. Mammals and birds are termed warm-blooded, or homeothermic, i.e., they are able to maintain a relatively constant inner body temperature, whereas other animals are cold-blooded, or poikilothermic, i.e.
..... Click the link for more information. ; feverfever,
elevation of body temperature above the normal level, which in humans is about 98&degF; (37&degC;) when measured orally. Fever is considered to be a symptom of a disorder rather than a disease in itself.
..... Click the link for more information. .

body temperature,

internal temperature of a living organism. Mammals and birds are termed warm-blooded, or homeothermic, i.e., they are able to maintain a relatively constant inner body temperature, whereas other animals are cold-blooded, or poikilothermic, i.e., their body temperature varies according to the temperature of the environment.

Warm-blooded Animals (Homeotherms)

In humans and other mammals, temperature regulation represents the balance between heat production from metabolic sources and heat loss from evaporation (perspiration) and the processes of radiation, convection, and conduction. In a cold environment, body heat is conserved first by constriction of blood vessels near the body surface and later by waves of muscle contractions, or shivering, which serve to increase metabolism. Shivering can result in a maximum fivefold increase in metabolism. Below about 40&degF; (4&degC;) a naked person cannot sufficiently increase the metabolic rate to replace heat lost to the environment. Another heat-conserving mechanism, goose bumps, or piloerection, raises the body hairs; although not especially effective in humans, in animals it increases the thickness of the insulating fur or feather layer.

In a warm environment, heat must be dissipated to maintain body temperature. In humans, increased surface blood flow, especially to the limbs, acts to dissipate heat at the surface. At environmental temperatures above 93&degF; (34&degC;), or at lower temperatures when metabolism has been increased by work, heat must be lost through the evaporation of the water in sweat. People in active work may lose as much as 4 quarts per hour for short periods. However, when the temperature and humidity are both high, evaporation is slowed, and sweating is not effective. Most mammals do not have sweat glands but keep cool by panting (evaporation through the respiratory tract) and by increased salivation and skin and fur licking.

Temperature regulatory mechanisms act through the autonomic nervous system and are largely controlled by the hypothalamus of the brain, which responds to stimuli from nerve receptors in the skin. Continued exposure to heat or cold results in some slow acclimatization, e.g., more active sweating in response to continued heat and an increase in subcutaneous fat deposits in response to continued cold.

Environmental extremes may result in failure to maintain normal body temperature. In both increased body temperature, or hyperthermia, and decreased body temperature, or hypothermia, death may result (see heat exhaustionheat exhaustion,
condition caused by overexposure to sunlight or another heat source and resulting in dehydration and salt depletion, also known as heat prostration. The symptoms are severe headaches, weakness, dizziness, blurred vision, and sometimes unconsciousness.
..... Click the link for more information. ). Controlled hypothermia is used in some types of surgery to temporarily decrease the metabolic rate. Feverfever,
elevation of body temperature above the normal level, which in humans is about 98&degF; (37&degC;) when measured orally. Fever is considered to be a symptom of a disorder rather than a disease in itself.
..... Click the link for more information. , caused by a resetting of the temperature regulatory mechanism, is a response to fever-causing, or pyrogenic, substances, such as bacterial endotoxins or leucocyte extracts. The upper limit of body temperature compatible with survival is about 107&degF; (42&degC;), while the lower limit varies.

In humans the inner body temperature alternates in daily activity cycles; it is usually lowest in early morning and is slightly higher at the late afternoon peak. In human females there is also a monthly temperature variation related to the ovulatory cycle. In many mammals and birds the body temperature shows more pronounced cyclic variations than in humans. For example, in hibernators the body temperature may lower to only a few degrees above the environmental temperature during the dormant periods; mammalian hibernators reawake spontaneously and in their active period are homeothermic.

Cold-blooded Animals (Poikilotherms)

Reptiles and other poikilothermic animals bask in warm weather and must hibernate in winter. The body temperature of fishes must remain close to that of the surrounding water, because heat is lost directly into the water during respiration. In the opah, bluefin tuna, and some other fishes, however, a special networks of blood vessels allow them to conserve metabolic heat and warm regions of their bodies. The mechanism of temperature regulation in homeotherms is considered an important evolutionary advance in that physical activity in such animals can be relatively independent of the environment.

Body Temperature

a complex indicator of the thermal state of animals and man. It results from the complex relations between the heat produced by the organs and tissues and the transfer of heat between the organs and tissues and the environment. In man and homeothermic animals, the body temperature is maintained by specialized thermoregulatory mechanisms at temperatures ranging from 36° to 39°C; the body temperature in birds ranges from 40° to 42°C.

Physiological fluctuations in the body temperature occurring during a 24-hour period follow circadian rhythms; in man, the difference between the body temperature in the early morning and in the evening varies from 0.5°–1.0°C. The differences in temperature among the internal organs amount to several tenths of a degree. The difference between the temperatures of the internal organs, muscles, and skin may vary as much as 5°–10°C. This makes it difficult to determine the average body temperature, which must be known in order to ascertain the thermal state of the body as a whole.

Body temperature is measured with a thermometer, which is usually placed in the armpit, rectum, mouth, or ear. In poikilotherms (cold-blooded animals), the body temperature differs little from the ambient temperature, and in some species it exceeds the ambient temperature only during intensive muscular activity.

The lowering or raising of body temperature (hypothermia and hyperthermia) by several degrees disturbs the body’s vital processes and may result in cooling, hyperpyrexia, or even death. In many diseases, such as fever, the body temperature rises to a certain level and is regulated at the new level.

REFERENCES

Burton, A., and O. Edholm. Chelovek v usloviiakh kholoda. Moscow, 1957. (Translated from English.)
Prosser, C. L., and F. Brown, Jr. Sravnitel’naia fiziologiia zhivotnykh. Moscow, 1967. (Translated from English.)
Hensel, H. “Neural Processes in Thermoregulation.” Physiological Reviews, 1973, vol. 53, no. 4.

K. P. IVANOV

body temperature

temperature

[tem´per-ah-chur] the degree of sensible heat or cold, expressed in terms of a specific scale. See Table of Temperature Equivalents in the Appendices. Body temperature is measured by a clinical thermometer and represents a balance between the heat produced by the body and the heat it loses. Though heat production and heat loss vary with circumstances, the body regulates them, keeping a remarkably constant temperature. An abnormal rise in body temperature is called fever.
Normal Body Temperature. Body temperature is usually measured by a thermometer placed in the mouth, the rectum, or the auditory canal (for tympanic membrane temperature). The normal oral temperature is 37° Celsius (98.6° Fahrenheit); rectally, it is 37.3° Celsius (99.2° Fahrenheit). The tympanic membrane temperature is a direct reflection of the body's core temperature. These values are based on a statistical average. Normal temperature varies somewhat from person to person and at different times in each person. It is usually slightly higher in the evening than in the morning and is also somewhat higher during and immediately after eating, exercise, or emotional excitement. Temperature in infants and young children tends to vary somewhat more than in adults.Temperature Regulation. To maintain a constant temperature, the body must be able to respond to changes in the temperature of its surroundings. When the outside temperature drops, nerve endings near the skin surface sense the change and communicate it to the hypothalamus. Certain cells of the hypothalamus then signal for an increase in the body's heat production. This heat is conducted to the blood and distributed throughout the body. At the same time, the body acts to conserve its heat. The arterioles constrict so that less blood will flow near the body's surface. 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.Abnormal Body Temperature. Abnormal temperatures occur when the body's temperature-regulating system is upset by disease or other physical disturbances. fever usually accompanies infection and other disease processes. In most cases when the oral temperature is 37.8°C (100°F) or over, fever is present. Temperatures of 40°C (104°F) or over are common in serious illnesses, although occasionally very high fever accompanies an illness that causes little concern. Temperatures as high as 41.7°C (107°F) or higher sometimes accompany diseases in critical stages. Subnormal temperatures, below 35.6°C (96°F) occur in cases of collapse; see also hypothermia" >symptomatic hypothermia.absolute temperature (T) that reckoned from absolute zero (−273.15°C), expressed on an scale" >absolute scale.basal body temperature (BBT) the temperature of the body under conditions of absolute rest; it has a slight sustained rise during the luteal phase of the cycle" >menstrual cycle and can be used as an indirect indicator of when ovulation has occurred.body temperature the temperature of the body of a human or animal; see temperature.core temperature the temperature of structures deep within the body, as opposed to peripheral temperature such as that of the skin.critical temperature that below which a gas may be converted to a liquid by increased pressure.normal temperature the body temperature usually registered by a healthy person, averaging 37°C (98.6°F).risk for imbalanced body temperature a nursing diagnosis accepted by the North American Nursing Diagnosis Association, defined as a state in which an individual is at risk of failure to maintain body temperature within the normal range.subnormal temperature temperature below the normal. See also hypothermia" >symptomatic hypothermia.

body temperature

The temperature of the human body, which is warmer at the core (centrally)—usually between 36–37.5ºC—than at the periphery (extremities).

Patient discussion about body temperature

Q. what is the red line when your body temperature drops before you are getting hypothermia? A. Hypothermia is a condition in which an organism's temperature drops below that required for normal metabolism and function. For people in stage 1 hypethermia, body temperature drops by 1-2°C below normal temperature (35-36°C). Mild to strong shivering occurs. In stage 2, body temperature drops by 2-4°C (35-33 degrees). Shivering becomes more violent. Muscle mis-coordination becomes apparent and movements are slow and labored and there is mild confusuin. In stage 3, body temperature drops below approximately 32 °C (89.6 °F). Shivering usually stops and there's difficulty speaking, sluggish thinking, and amnesia start to appear. Cellular metabolic processes shut down. This is life threatening.

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body temperature

body temperature

temperature, body:

body temperature,

Warm-blooded Animals (Homeotherms)

Cold-blooded Animals (Poikilotherms)

Body Temperature

REFERENCES

body temperature

temperature

body temperature

Patient discussion about body temperature

body temperature

Synonyms for body temperature

noun temperature of the body

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