STANDARD METABOLISM

From Big Medical Encyclopedia

STANDARD METABOLISM — the minimum quantity of energy necessary for maintenance of life of an organism in a condition of absolute rest. The lake of the lake reflects intensity of the metabolic processes in an organism directed to maintenance of constantly proceeding vital functions. A considerable part of this energy is spent for ensuring activity of cardiovascular and respiratory systems, hemadens, kidneys, a liver, went. - kish. path and other bodies.

Lakes of the lake define at the awake person who is in a condition of absolute muscular and emotional rest at a comfortable temperature (18 — 20 °), in the morning on an empty stomach, i.e. not less than in 12 — 16 hours after the last meal, at an exception of proteins of a diet for 2 — 3 days before definition. Lakes of the lake express the number of the kilocalories (kcal) allocated with an organism in the specified conditions on 1 kg of the weight (weight) or on 1 m 2 body surfaces in 1 hour or in 1 days, or according to the International System of Units (SI) in kilojoules (kJ).

Most of researchers consider that standard metabolism is invariable size for this organism. At the same time, being an integral indicator of intensity of oxidizing processes in fabrics at rest, O. of the lake in a certain measure depends from funkts, conditions of nervous and endocrine systems, fiziol, conditions of internals, and also external impacts on an organism. Level O. of the lake can change at insufficient or excess food, long increase or decrease in exercise stresses, impact on an organism of climatic factors etc. At various people the size O. of the lake depends hl. obr. from age, growth, body weight, a floor. At the adult healthy person the level O. of the lake

averages 1600 — 1700 kcal/days, and at women it is 10 — 15% lower, than at men. At newborns, according to different researchers, O. the lake makes from 46 to 54 kcal! kg! days. At the child within the first months of life heat production increases and reaches a maximum by the beginning of the second year, exceeding heat generation of the adult by 1,5 — 2 times. In process of growth O.'s indicators of the lake decrease in the beginning quickly, then more slowly and by 16 — 17 years approach the sizes characteristic of the adult. In further O. the lake decreases even more.

The high level of O. of the lake at children's age is explained by the large number of protoplasmatic weight, high metabolic activity strengthened by growth of fabrics. At senile age along with decrease in quantity and activity of cells also muscular activity decreases that also affects the level O. of the lake

of O. of the lake at same-gender persons, age and a constitution is approximately identical size if conditions of its definition are strictly met. At recalculation of intensity of O. of the lake on 1 kg of body weight at hematothermal animal different types big differences, at the same time are observed the animal is less, the level O. of the lake on 1 kg of the weight (tab.) is higher. At recalculation of intensity of O. of the lake on 1 sq.m of a body surface the received sizes differ not so sharply, as at recalculation on 1 kg of body weight.

M. Rubner (1883) formulated the law of a body surface, according to Krom intensity of exchange is proportional to the size of a body surface. However this law has relative value and allows to carry out only approximate calculations of the energy emitted by an organism.

Character of food (total quantity and structure of food) exerts impact on the size O. of the lake at rest. Besides, directly meal causes the increase in metabolic rate continuing within 5 — 6 hour. Such influence of food on the level of a metabolism and energy carries the name of specific dynamic effect of food.

Most of researchers explain the mechanism of specific dynamic effect of food or immediate effect on a cell of decomposition products of food or products of an intermediate metabolism, or change funkts, activity went. - kish. path, i.e. activation of a vermicular movement of intestines and strengthening of work of digestive glands. R. P. Olnyanskaya (1949) installed also difficult reflex mechanism of specific dynamic effect of food.

Lead also long restriction of food, the excess consumption of food increased or insufficient contents in a diet of separate nutrients to change of level O. of the lake.

The level O. of the lake is influenced also by a thermal factor: long impact on an organism of animals and the person of low temperature raises O. of the lake (at temperature drop of air on 10 ° the level O. of the lake increases by 2,5%); high temperature reduces O. of the lake, i.e. there is its adaptation to ambient temperature.

At the person and animal O. the lake varies for days, changes on days, during various seasons of year; during sleep it decreases by 13% (due to relaxation of skeletal muscles). Seasonal changes of O. of the lake at the person consist in increase in its spring and in the early summer and decrease late fall and in the winter. Seasonal changes are connected not so much with a thermal factor how many with change of a physical activity, fluctuations of hormonal activity of an organism etc. (see. Biological rhythms ).

O.'s definition by the lake is of great importance in applied medicine at diagnosis of nek-ry diseases. Islands calculate the lake by means of tables, in to-rykh the body weight, growth, age and a sex of the examinee, and also calorimetric methods is considered (see. Calorimetry ) or the method of an indirect calorimetry based on a research gas exchange (see).

Pathological physiology. At O.'s definition by the lake often note a deviation of its indicators from norm. However only considerable (10 — 15%) O.'s deviations by the lake from average normal values can indicate it true disturbance. It is especially important to consider it in experimental medicine as for animals it is very difficult to reproduce necessary conditions of definition of O. of the lake.

According to the existing representations, the general heat production of an organism (see. Heat production ) it consists of primary and secondary warmth. Primary warmth is a result of dispersion of energy of oxidation of substrates in a chain of transport of electrons, secondary — a consequence of use for this or that cellular function of the makroer-gichesky connections which are formed during tissue respiration. The main cellular mechanisms of disturbances of O. of the lake come down to change of intensity of formation of primary or secondary warmth or both of its types together. Change of each of these processes is followed by change of oxygen consumption — the most widespread criterion of size O. of the lake. In case of the strengthened expenditure of makroergichesky connections on different types of «work» of a cell becomes effective respiratory control in mitochondrions, the essence to-rogo is that the product of dephosphorylation of ATP is a powerful stimulator of tissue respiration. During the easing or full removal of respiratory control («friable» interface or dissociation of oxidizing phosphorylation) the strengthened oxygen consumption usually is registered (see. biological oxidation ).

At O.'s definition by the lake it is necessary to consider a possibility of discrepancy of data of a direct and indirect calorimetry that it is connected with short duration of definition of oxygen consumption. At longer definitions (about 24 hours) results of both methods shall, obviously, completely to match. Distortion of idea of O. of the lake can be connected with the fact that the caloric value of oxygen is various depending on character of the substrates (proteins, fats or carbohydrates) which are preferential oxidized in an organism in the course of gas exchange. Exact calculation of true heat production requires registration not only oxygen consumption, but also respiratory coefficient (see). Character of the oxidized substrates depends, on the one hand, on character of the previous food, and with another — on a state. processes about» exchange of substances in general. Therefore even normal amounts of O. of the lake at change of a respiratory coefficient can indicate disbolism (e.g., a low respiratory coefficient at normal O. the lake at patients with a diabetes mellitus without manifestations of a ketosis).

Pathology of a nervous system can cause O.'s change by the lake as as a result of direct disturbance of formation of primary warmth, and owing to change of intensity of functioning of this or that body or fabric. An example of the first mechanism are, apparently, defeats of the diencephalic vegetative centers (injuries, tumors, hemorrhages and t. and.), reproduced in an experiment by «thermal pricks» in subcrustal educations. The second mechanism causes O.'s decrease of the lake at paralyzes and increase it at the strengthened functioning of a respiratory organs, blood circulations, muscles and, apparently, a liver. Value of changes of activity of various bodies for emergence of shifts in O. of the lake is not identical. So, intense activity of a brain or kidneys influences a little the overall heat balance of an organism whereas muscular contractions, cardiac performance and a respiratory organs play the defining role in the general heat production of an organism.

Considerable impact on O. of the lake is exerted by a tone of vegetative (preferential sympathetic) nervous system since the mediators developed by it are directly involved in thermal controls (see). Tumors of chromaffin fabric (pheochromocytoma) cosecreting adrenaline and noradrenaline are followed by sharp increase in O. of the lake. Removal sympathetic gangliyev and a medulla of adrenal glands, on the contrary, can lower O. of the lake. In addition to influence on function of internals, these mediators, apparently, can affect also processes of formation of primary warmth, but the mechanism of this their effect is yet not completely clear.

Most often the diseases of a thyroid gland which are followed raised or hyposecretion of the thyroid hormones which are carrying out a specific role of regulators of intensity of tissue respiration and energy balance in an organism are the reason of change of O. of the lake at various types of endocrine pathology. O.'s increase of the lake is the most constant, pathognomonic sign of a hyperthyroidism (thyrotoxicosis) accompanying very widespread endocrine diseases — a diffusion toxic craw, thyrocardiac adenoma, etc. On the contrary, depression of function of a thyroid gland (hypothyroidism) causes O.'s reduction by the lake. The lake can be the cornerstone of effect of thyroid hormones on O. a number of mechanisms: activation membrane To, Na-ATF-azy of cells, activation of synthesis of macromolecules, oxidizing enzymes and mitochondrial respiratory enzymes. High doses of thyroid hormones are capable to separate oxidizing phosphorylation in mitochondrions, increasing thus formation of primary warmth. A significant role in increase in Q. the lake at a thyrotoxicosis (and decrease it at a hypothyroidism) plays also change of level of functioning cardiovascular and other systems of an organism. Especially substantial increase of O. of the lake (to 150%), and also discrepancy of indicators of a direct and indirect calorimetry (the gain of heat production inadequate to oxygen consumption) is characteristic of a thyrotoxicosis that is registered in the conditions of dissociation of the oxidizing phosphorylation caused and other agents.

The expressed O.'s changes by the lake are observed at pathology of a front share of a hypophysis, to-ry regulates activity of a thyroid gland (e.g., O.'s decrease of the lake at a hypopituitarism or removal of a hypophysis).

About a role of other hormones in genesis of mechanisms of disturbance of O. of the lake of the data are less certain. The hypocorticoidism usually is followed by O.'s decrease of the lake, however at patients with an addisonovy disease its decrease is a non-constant symptom. Hormone of a pancreas insulin reduces O. of the lake due to the oppressing action on muscular contractions and catabolic processes. Ability of this hormone to reduce heat production is used at experimental hibernation. Removal of a pancreas, and also a diabetes mellitus lead to O.'s increase of the lake that is probably caused not only loss of direct effect of insulin on heat production, but also metabolic changes, in particular increase in level free fat to - t and ketone bodies, to-rye in big concentration are capable to separate oxidizing phosphorylation.

O.'s changes by the lake are often observed at various intoxications of an organism, infectious and feverish diseases. At the same time independence of stimulation of oxidizing processes of the fact of existence of fever is revealed. Effect of 2,4-a-dinitrophenol is the most studied, to-ry it is considered a classical razobshchitel of oxidizing phosphorylation. O.'s increase of the lake at dinitrofeno-lovy intoxication, as well as at effect of thyroid hormones, is characterized by the large increase of heat production disproportionate to oxygen consumption. Other toxins can raise O. of the lake or due to dissociation of oxidizing phosphorylation (diphtheritic, staphylococcal and streptococcal toxins, salicylates), or at the expense of others, not until the end of the found-out reasons (e.g., endotoxins). At the same time various options of discrepancy of results of a direct and indirect calorimetry are possible. There are data that O.'s increase of the lake caused by infectious and toxic agents is connected with effect of hormones of a thyroid gland.

O.'s increase of the lake is characteristic of late stages of development of malignant tumors and especially leukoses. The reasons of it are not quite established, but, apparently, the cellular growth as the process which is followed by the strengthened disintegration of makroergichesky connections with increase in formation of secondary warmth does not exhaust hmekhanizm of increase in heat production in these cases.

The hypoxia is usually characterized by O.'s increase of the lake due to increase in function of a respiratory organs and blood circulation, and also accumulation of toxic products of interstitial exchange. At the same time very heavy degrees of a hypoxia are followed by O.'s decrease of the lake. In the analysis of influence of a hypoxia it is necessary to consider its frequent combination to a hypercapnia as considerable excess of carbonic acid oppresses heat production. Anemias usually proceed with O.'s increase of the lake, in genesis to-rogo toxic products of metabolism can also play a role. Among the factors causing O.'s change by the lake it is necessary to mention long starvation, at Krom the mechanisms of sharp restriction of energy expenditure leading to O.'s decrease of the lake turn on.

O.'s definition by the lake at various patol, states, apparently, has no absolute diagnostic value and serves as rather auxiliary method of a research allowing to expand ideas of a pathogeny of this disease and causing use special to lay down. actions. However considering the central role of thyroid hormones in regulation of energy balance of an organism, it is necessary every time at registration of the expressed O.'s deviations by the lake from norm especially carefully to investigate function thyroid gland (see).

See also Metabolism and energy .

&Tablitsa.Nbsp; STANDARD METABOLISM AT the PERSON AND SOME ANIMALS (in terms of &1nbsp; &kgnbsp; weight and on &1nbsp; m 2   body surfaces)




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V. A. Makarov; V. I. Kandror (stalemate. physical.).

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