BODY TEMPERATURE

From Big Medical Encyclopedia

BODY TEMPERATURE — complex indicator of a thermal condition of an organism of animals and person.

Maintenance of T. t. in certain limits is one of the most important conditions of normal life activity of an organism. At poikilothermic animals (see), to the Crimea invertebrates, fishes, Amphibia, reptiles, T belong. t. it is close to ambient temperature. Gomoyotermny animals (see) — birds and mammals — in the course of evolution gained ability to support constant T. t. at temperature variations of the environment.

In a gomoyotermny organism conditionally distinguish two temperature zones — a cover and a kernel. The cover is made by superficially located structures and fabrics — skin, connecting fabric, a kernel — blood, internals and systems. Temperature of a kernel is higher, than covers, and is rather stable: the difference of temperatures between internals makes several tenth degree, and the liver has the most high temperature (about 38 °). Temperature of other internals, including brain, is close to temperature of blood in the aorta determining the average temperature of a kernel. In a brain at rabbits and nek-ry other animals the difference of temperature of a cerebral cortex and a hypothalamus reaching 1 ° is noted.

Temperature of a cover is lower than temperature of a kernel on 5 — 10 ° and is not identical on different body parts that it is connected with distinction of their blood supply, the size of a hypodermic fatty layer, etc. Surface temperature of a body significantly depends on ambient temperature. At short-term heating of a body (e.g., in the Finnish sauna at air temperature 80 — 100 °) temperature of skin of extremities, a component normal about 30 °, can rise to 45 — 48 °, and during the cooling to fall to 5 — 10 °.

Distribution of temperature (in degrees) on a body surface of the person is normal.

Existence in an organism of zones with a different temperature does not allow to define T unambiguously. t. For its characteristic often use a concept of the weighted average temperature, to-ruyu calculate as average of temperatures of all body parts. More precisely T. t. it can be characterized by the temperature scheme — distribution of temperature on a body surface (fig.) or in its kernel. Also the characteristic of T is used. t. a gradient of temperature, to-ry it is represented by the vector directed towards the greatest value of temperature, and the size of a vector corresponds to the change of temperature having per unit length. The image of a temperature body scheme in the form of isotherms and values of a gradient mutually supplement each other: what closer located isotherms, subjects body parts have a bigger gradient of temperatures.

Measurement of T. t. make by means of various thermometers and sensors of temperature (ShM. Thermometry). Temperature of a kernel rather precisely (with a mistake less than 0,5 °) can be taken, placing the thermometer in an axillary hollow, under language, in a rectum or outside acoustical pass. Normal T. t. the person, measured in a rectum, it is close to 37 °. Temperature taken under language is 0,2 — 0,3 less °, in an axillary hollow is 0,3 — 0,4 less °.

At most of people daily fluctuations of T are well-marked. t., lying in the range of 0,1 — 0,6 °. The highest T. t. the lowest is observed in the second half of day — at night. Take place and seasonal fluctuations of T. t.: in the summer it on 0,1 — 0,3 ° above, than in the winter. At women also monthly rhythm of change of T is expressed. t.: at an ovulation it raises on 0,6 — 0,8 °. Fervescence is observed at hard muscular work, strong emotional experiences.

Maintenance of life at gomoyotermny animals and the person perhaps only in the certain range of T. t. (see Overheating of an organism, Cooling of an organism). The interval between the standard and upper lethal temperature of internals makes about 6 °. The person and the highest mammals have upper lethal temperature is about 43 °, at birds 46 — 47 °. Causes of death of gomoyotermny animals and the person at exceeding T.T. an upper critical limit consider disturbance of biochemical balance in an organism owing to influence of change of temperature on speeds of different biochemical reactions, and also disturbance of structure of membranes as a result of thermal change of conformation of macromolecules, the thermal inactivation of enzymes going with a speed exceeding the speed of their synthesis, a denaturation of proteins as a result of heating, a lack of oxygen. The lower lethal body temperature makes 15 — 23 °. At artificial cooling of an organism (see. Hypothermia artificial ), when special measures are taken for preservation of its viability, by T. t. it is possible to lower up to lower sizes without risk for life.

Maintenance of constant T. t. at the person and gomoyotermny animals it is carried out by interaction of mechanisms heats production (see) and thermolyses (see). Stability of core temperature at the same time is provided with functional system, in to-ruyu thermoreceptors of skin, vessels, a hypothalamus, the centers of thermal control in a brain and the efferent mechanisms regulating heat production and a thermolysis are included. At temperature increase of blood the thermolysis amplifies — vessels of skin extend, heat waste convection, radiation, in the way of evaporation of sweat increases, mechanisms of heat production are at the same time stopped. At decrease in T. t. the thermolysis at the expense of vasoconstriction of skin and reduction of its heat conductivity decreases, heat production due to increase in muscle performance grows. At the beginning of cooling the thermoregulatory muscle tone (nesokratitelny thermogenesis) increases, and at deeper cooling the muscular shiver (sokratitelny thermogenesis) arises and accrues. At long and regular coolings the mechanism of chemical thermal control causing strengthening of metabolism of cells and growth of heat production turns on.

T. t. is one of the most important indicators of a condition of an organism. Temperature increase on 1 — 2 ° often is a sign to pathology (see. Fever ). To a disease can point also smaller temperature increase (to 0,5 ° below), the keeping long time or arising periodically (see. Subfebrile condition ).

Long increase in T. t. svya-zeno with the change of thermoregulation caused by education in an organism of specific substances — pyrogens, to-rye change limits of normal installation T. t. centers of thermal control. Pyrogens appear at action on an organism of pathogenic bacteriums, viruses, endotoxins. The temperature increase (a feverish state) arising under the influence of pyrogens is the adaptive reaction of an organism developed in the course of evolution, leads edges to accumulation of additional heat, stimulates exchange processes and in most cases promotes fight of an organism against pathogenic factors. Local temperature increase can happen at local inflammatory processes, development of tumors. Fall of temperature of separate body parts is observed at diseases of the vessels leading to reduction of a local blood-groove — vasomotor spasms, occlusions, obliterations. Measurement of local temperature by means of special sensors or thermal imagers (see Thermometry, Termografiya) allows to make timely the diagnosis, to localize disturbance of passability of a vessel, to predict dynamics of a disease.

Features of body temperature at children

At children of T. t. it is characterized by relative constancy and is defined by anatomo-physiological features of a children's organism: big, than adults, the relation have body surfaces to its weight and imperfection of mechanisms of thermal control. For maintenance of constant temperature the organism of the child shall develop more heat on 1 kg of body weight in comparison with an organism of the adult. Respectively basal metabolic rate at children, especially the first months of life, in terms of weight is much higher, than at the adult. Imperfection of mechanisms of thermoregulation is shown by restriction of sweating at newborns, high thermal conductivity of the skin tied with features of its structure and underdevelopment of a layer of a hypodermic fatty tissue, immaturity of sokratitelny thermogenesis (a muscular shiver) because of an underdevelopment of the center of thermal control in a hypothalamus.

T. t. at children measure in an axillary hollow, an oral cavity and a rectum. At the newborn T. t. in an axillary hollow after the initial decrease caused by the Cold stress in the first 4 days of life it is supported at the level of 37,2 ° then is established at the level of lower than 37 °. At the baby temperature in an axillary hollow makes 36,7 ^ 0,4 °, in a rectum 37,8 ^ 0,4 °. The same temperature is inherent also to children of advanced age.

Daily fluctuations of T. t. at the healthy full-term newborns in the first 10 days of life are absent, but in process of growth of the child begin to be shown more and more clearly. On the first month of life minimum T. t. it is observed between 10 — 11 and 19 — 24 hours, and maximum between 6 — 9 and 16 — 18 hours. A difference between day and night T. t. makes at children of the first month of life 0,4 — 0,5 °, the second 0,5 — 0,6 °, 4 — 6 months 0,8 — 1,2 °, at the age of one year 1,5 °. Temperature variations of a body within a day depend on an emotional condition of the child, a physical activity, clothes, ambient temperature.

Sharp fluctuations of T are characteristic of premature children. t. within a day, intensity to-rykh depends on age and degree of prematurity, lack of daily periodicity of T. t. and differences of temperatures of skin between distal and proximal segments of extremities that testifies to the expressed imperfection of the central mechanisms of thermal control. Rectal temperature at premature children of the first 10 days of life is lower, than at full-term, and averages 35,3 °, to monthly age it reaches 37,2 °.

Increase in T. t. at children can be a consequence as delays of a thermolysis, napr, at long subfebrile condition (see), and strengthenings of heat production, napr, at thyrotoxicosis (see). Increase in T. t. at children of early age can have an infectious and noninfectious origin. In the latter case it is connected with the wrong hygienic keeping of the child, overheating, dehydration, constant locks, etc. At children of advanced age infections (preferential virus origin), collagenic diseases, malignant new growths, diseases of closed glands, etc. can be the cause of fervescence. At nek-ry patol. states, napr, hypothyroidism (see), fall of temperature of a body is observed.

See also Thermal control .



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E. A. Umryukhin, I. P. Bryazgunov (ped.).

Яндекс.Метрика