Topic 10. AGE CHARACTERISTICS OF METABOLISM AND ENERGY

10.1. Characteristics of metabolic processes

The metabolism and energy is the basis of the life processes of the body. In the human body, in its organs, tissues, cells, there is a continuous process of synthesis, i.e., the formation of complex substances from simpler ones. At the same time, decomposition and oxidation of complex organic substances that make up the cells of the body occur.

The work of the body is accompanied by its continuous renewal: some cells die, others replace them. In an adult, 1/20 of the cells of the skin epithelium, half of all epithelial cells of the digestive tract, about 25 g of blood, etc. die and are replaced during the day. Growth and renewal of body cells are possible only if oxygen and nutrients are continuously supplied to the body. Nutrients are precisely the building and plastic material from which the body is built.

For continuous renewal, building new cells of the body, the work of its organs and systems - the heart, gastrointestinal tract, respiratory apparatus, kidneys and others, energy is needed for a person to do work. A person receives this energy during decay and oxidation in the process of metabolism. Consequently, the nutrients entering the body serve not only as a plastic building material, but also as a source of energy necessary for the normal functioning of the body.

Thus, metabolism is understood as a set of changes that substances undergo from the moment they enter the digestive tract and until the formation of final decay products excreted from the body.

Anabolism and catabolism. Metabolism, or metabolism, is a finely coordinated process of interaction between two mutually opposite processes occurring in a certain sequence. Anabolism is a set of biological synthesis reactions that require energy. Anabolic processes include the biological synthesis of proteins, fats, lipoids, and nucleic acids. Due to these reactions, simple substances entering cells, with the participation of enzymes, enter into metabolic reactions and become substances of the body itself. Anabolism creates the basis for the continuous renewal of worn-out structures.

Energy for anabolic processes is supplied by catabolism reactions, in which molecules of complex organic substances are broken down with the release of energy. The end products of catabolism are water, carbon dioxide, ammonia, urea, uric acid, etc. These substances are not available for further biological oxidation in the cell and are removed from the body.

The processes of anabolism and catabolism are inextricably linked. Catabolic processes supply energy and precursors for anabolism. Anabolic processes ensure the construction of structures that go to the restoration of dying cells, the formation of new tissues in connection with the growth processes of the body; provide the synthesis of hormones, enzymes and other compounds necessary for the life of the cell; supply macromolecules to be cleaved for catabolism reactions.

All metabolic processes are catalyzed and regulated by enzymes. Enzymes are biological catalysts that "start" reactions in the body's cells.

Transformation of substances. Chemical transformations of food substances begin in the digestive tract, where complex food substances are broken down into simpler ones (most often monomers), which can be absorbed into the blood or lymph. Substances received as a result of absorption into the blood or lymph are brought into the cells, where they undergo major changes. Complex organic compounds formed from the incoming simple substances are part of the cells and take part in the implementation of their functions. The transformations of substances that occur inside cells constitute the essence of intracellular metabolism. A decisive role in intracellular metabolism belongs to numerous cell enzymes that break intramolecular chemical bonds with the release of energy.

Oxidation and reduction reactions are of primary importance in energy metabolism. With the participation of special enzymes, other types of chemical reactions are also carried out, for example, reactions of transferring a phosphoric acid residue (phosphorylation), an NH2 amino group (transamination), a CH3 methyl group (transmethylation), etc. The energy released during these reactions is used to build new substances in the cell, to keep the body alive.

The end products of intracellular metabolism are partly used to build new cell substances; substances not used by the cell are removed from the body as a result of the activity of the excretory organs.

ATP. The main accumulating and energy-transferring substance used in the synthetic processes of both the cell and the whole organism is adenosine triphosphate, or adenosine triphosphate (ATP). The ATP molecule consists of a nitrogenous base (adenine), a sugar (ribose) and phosphoric acid (three phosphoric acid residues). Under the influence of the enzyme ATPase, the bonds between phosphorus and oxygen in the ATP molecule are broken and a water molecule is added. This is accompanied by the elimination of a phosphoric acid molecule. The cleavage of each of the two terminal phosphate groups in the ATP molecule occurs with the release of large amounts of energy. As a result, the two terminal phosphate bonds in the ATP molecule are called energy-rich bonds, or high-energy bonds.

10.2. The main forms of metabolism in the body

Protein metabolism. The role of proteins in metabolism. Proteins occupy a special place in metabolism. They are part of the cytoplasm, hemoglobin, blood plasma, many hormones, immune bodies, maintain the constancy of the body’s water-salt environment, and ensure its growth. Enzymes that are necessarily involved in all stages of metabolism are proteins.

Biological value of food proteins. The amino acids used to build the body's proteins are unequal. Some amino acids (leucine, methionine, phenylalanine, etc.) are essential for the body. If an essential amino acid is missing from food, protein synthesis in the body is severely disrupted. Amino acids that can be replaced by others or synthesized in the body itself during metabolism are called non-essential.

Food proteins containing all the necessary set of amino acids for normal protein synthesis of the body are called complete. These include mainly animal proteins. Food proteins that do not contain all the amino acids necessary for protein synthesis of the body are called defective (for example, gelatin, corn protein, wheat protein). The proteins of eggs, meat, milk, and fish have the highest biological value. With a mixed diet, when food contains products of animal and vegetable origin, a set of amino acids necessary for protein synthesis is usually delivered to the body.

The intake of all essential amino acids for a growing organism is especially important. For example, the absence of the amino acid lysine in food leads to a delay in the growth of the child, to the depletion of his muscular system. A lack of valine causes a disorder of the vestibular apparatus in children.

Of the nutrients, only nitrogen is included in the composition of proteins, therefore, the quantitative side of protein nutrition can be judged by the nitrogen balance. Nitrogen balance - this is the ratio of the amount of nitrogen received during the day with food, and the nitrogen excreted per day from the body with urine, feces. On average, the protein contains 16% nitrogen, i.e. 1 g of nitrogen is contained in 6,25 g of protein. Multiplying the amount of absorbed nitrogen by 6,25, you can determine the amount of protein received by the body.

In an adult, nitrogen balance is usually observed - the amounts of nitrogen introduced with food and excreted with excretion products coincide. When more nitrogen enters the body with food than it is excreted from the body, they speak of a positive nitrogen balance. Such a balance is observed in children due to an increase in body weight with growth, during pregnancy, and with great physical exertion. A negative balance is characterized by the fact that the amount of nitrogen introduced is less than that excreted. It can be with protein starvation, serious illnesses.

Breakdown of proteins in the body. Those amino acids that did not go into the synthesis of specific proteins undergo transformations, during which nitrogenous compounds are released. Nitrogen is split off from the amino acid as ammonia (NH3) or as the amino group NH2. An amino group, having split off from one amino acid, can be transferred to another, due to which the missing amino acids are built. These processes occur mainly in the liver, muscles, and kidneys. The nitrogen-free residue of the amino acid undergoes further transformations with the formation of carbon dioxide and water.

Ammonia, formed during the breakdown of proteins in the body (a poisonous substance), is neutralized in the liver, where it turns into urea; the latter in the urine is excreted from the body.

The end products of protein breakdown in the body are not only urea, but also uric acid and other nitrogenous substances. They are excreted from the body with urine and sweat.

Features of protein metabolism in children. In the child’s body, intensive processes of growth and formation of new cells and tissues occur. The protein requirement of a child's body is greater than that of an adult. The more intense the growth processes, the greater the need for protein.

In children, a positive nitrogen balance is observed, when the amount of nitrogen introduced with protein foods exceeds the amount of nitrogen excreted in the urine, which provides the growing body's need for protein. The daily requirement for protein per 1 kg of body weight in a child in the first year of life is 4-5 g, from 1 to 3 years - 4-4,5 g, from 6 to 10 years - 2,5-3 g, over 12 years old - 2-2,5 g, in adults - 1,5-1,8 g. It follows that, depending on age and body weight, children from 1 to 4 years old should receive 30-50 g of protein per day, from 4 to 7 years old - about 70 g, from 7 years old - 75-80 g. With these indicators, nitrogen is retained in the body as much as possible. Proteins are not stored in the body in reserve, so if you give them with food more than the body needs, then an increase in nitrogen retention and an increase in protein synthesis will not occur. Too low amount of protein in food causes the child to lose appetite, disturbs the acid-base balance, increases the excretion of nitrogen in the urine and feces. The child needs to be given the optimal amount of protein with a set of all the necessary amino acids, while it is important that the ratio of the amount of proteins, fats and carbohydrates in the child's food is 1:1:3; under these conditions, nitrogen is maximally retained in the body.

In the first days after birth, nitrogen makes up 6-7% of the daily amount of urine. With age, its relative content in the urine decreases.

Fat metabolism. The importance of fats in the body. Fat received from food in the digestive tract is broken down into glycerol and fatty acids, which are absorbed mainly into the lymph and only partially into the blood. Through the lymphatic and circulatory systems, fats enter adipose tissue. There is a lot of fat in the subcutaneous tissue, around some internal organs (for example, kidneys), as well as in the liver and muscles. Fats are part of cells (cytoplasm, nucleus, cell membranes), where their quantity is constant. Accumulations of fat can serve other functions. For example, subcutaneous fat prevents increased heat transfer, perinephric fat protects the kidney from bruises, etc.

Fat is used by the body as a rich source of energy. With the breakdown of 1 g of fat in the body, more than two times more energy is released than with the breakdown of the same amount of proteins or carbohydrates. The lack of fat in food disrupts the activity of the central nervous system and reproductive organs, reduces endurance to various diseases.

Fat is synthesized in the body not only from glycerol and fatty acids, but also from the metabolic products of proteins and carbohydrates. Some unsaturated fatty acids necessary for the body (linoleic, linolenic and arachidonic) must be supplied to the body in finished form, since it is not able to synthesize them on its own. Vegetable oils are the main source of unsaturated fatty acids. Most of them are in linseed and hemp oil, but there is a lot of linoleic acid in sunflower oil.

Vitamins soluble in them (A, D, E, etc.), which are of vital importance for humans, enter the body with fats.

For 1 kg of adult weight per day, 1,25 g of fat should be supplied with food (80-100 g per day).

The end products of fat metabolism are carbon dioxide and water.

Features of fat metabolism in children. In a child’s body, from the first six months of life, fats cover approximately 50% of the energy requirement. Without fats, it is impossible to develop general and specific immunity. Fat metabolism in children is unstable; if there is a lack of carbohydrates in food or with increased consumption, the fat depot is quickly depleted.

Absorption of fats in children is intensive. With breastfeeding, up to 90% of milk fats are absorbed, with artificial feeding - 85-90%. In older children, fats are absorbed by 95-97%.

For a more complete use of fat in the diet of children, carbohydrates must be present, since with their lack in nutrition, incomplete oxidation of fats occurs and acidic metabolic products accumulate in the blood.

The body's need for fat per 1 kg of body weight is higher, the younger the child. With age, the absolute amount of fat necessary for the normal development of children increases. From 1 to 3 years, the daily requirement for fat is 32,7 g, from 4 to 7 years - 39,2 g, from 8 to 13 years - 38,4 g.

Carbohydrate metabolism. The role of carbohydrates in the body. Over the course of a lifetime, a person eats about 10 tons of carbohydrates. They enter the body mainly in the form of starch. Having broken down into glucose in the digestive tract, carbohydrates are absorbed into the blood and absorbed by cells. Plant foods are especially rich in carbohydrates: bread, cereals, vegetables, fruits. Animal products (with the exception of milk) are low in carbohydrates.

Carbohydrates are the main source of energy, especially with increased muscle work. In adults, more than half of the energy the body receives from carbohydrates. The breakdown of carbohydrates with the release of energy can proceed both in anoxic conditions and in the presence of oxygen. The end products of carbohydrate metabolism are carbon dioxide and water. Carbohydrates have the ability to quickly break down and oxidize. With severe fatigue, with great physical exertion, taking a few grams of sugar improves the condition of the body.

In the blood, the amount of glucose is maintained at a relatively constant level (about 110 mg%). A decrease in glucose content causes a decrease in body temperature, a disorder in the activity of the nervous system, and fatigue. The liver plays a large role in maintaining a constant blood sugar level. An increase in the amount of glucose causes its deposition in the liver in the form of a reserve animal starch - glycogen, which is mobilized by the liver with a decrease in blood sugar. Glycogen is formed not only in the liver, but also in the muscles, where it can accumulate up to 1-2%. Glycogen reserves in the liver reach 150 g. During starvation and muscular work, these reserves are depleted.

If the content of glucose in the blood increases to 0,17%, then it begins to be excreted from the body with urine; as a rule, this occurs when eating a large amount of carbohydrates in food. This is another mechanism for regulating blood sugar levels.

However, there may be a persistent increase in blood sugar. This occurs when the function of the endocrine glands is impaired. Violation of the functioning of the pancreas leads to the development of diabetes mellitus. With this disease, the ability of body tissues to absorb sugar is lost, as well as to convert it into glycogen and store it in the liver. Therefore, the level of sugar in the blood is constantly elevated, which leads to increased excretion of it in the urine.

The value of glucose for the body is not limited to its role as an energy source. It is part of the cytoplasm and therefore necessary for the formation of new cells, especially during the growth period. Carbohydrates are also included in the composition of nucleic acids.

Carbohydrates are also important in the metabolism in the central nervous system. With a sharp decrease in the amount of sugar in the blood, there are sharp disorders in the activity of the nervous system. There are convulsions, delirium, loss of consciousness, changes in the activity of the heart. If such a person is injected with glucose into the blood or given to eat ordinary sugar, then after a while these severe symptoms disappear.

Completely sugar from the blood does not disappear even in the absence of it in food, since in the body carbohydrates can be formed from proteins and fats.

The need for glucose in different organs is not the same. The brain retains up to 12% of glucose brought in, intestines - 9%, muscles - 7%, kidneys - 5%. The spleen and lungs almost do not detain it at all.

Carbohydrate metabolism in children. In children, carbohydrate metabolism occurs with great intensity, which is explained by the high level of metabolism in the children's body. Carbohydrates in a child’s body not only serve as the main source of energy, but also play an important plastic role in the formation of cell membranes and connective tissue substances. Carbohydrates also participate in the oxidation of acidic products of protein and fat metabolism, which helps maintain acid-base balance in the body.

The intensive growth of the child's body requires significant amounts of plastic material - proteins and fats, so the formation of carbohydrates in children from proteins and fats is limited. The daily requirement for carbohydrates in children is high and amounts to 10-12 g per 1 kg of body weight in infancy. In subsequent years, the required amount of carbohydrates ranges from 8-9 to 12-15 g per 1 kg of weight. A child aged 1 to 3 years should be given an average of 193 g of carbohydrates per day with food, from 4 to 7 years - 287 g, from 9 to 13 years - 370 g, from 14 to 17 years - 470 g, for an adult - 500 G.

Carbohydrates are absorbed by the child's body better than adults (in infants - by 98-99%). In general, children are relatively more tolerant of high blood sugar than adults. In adults, glucose appears in the urine if it enters 2,5-3 g per 1 kg of body weight, and in children this occurs only when 8-12 g of glucose per 1 kg of body weight enters. Taking small amounts of carbohydrates with food can cause a two-fold increase in blood sugar in children, but after 1 hour the blood sugar begins to decrease and after 2 hours it is completely normal.

Water and mineral metabolism. Vitamins. The importance of water and mineral salts. All transformations of substances in the body take place in an aquatic environment. Water dissolves nutrients that enter the body and transports dissolved substances. Together with minerals, it takes part in the construction of cells and in many metabolic reactions. Water is involved in the regulation of body temperature: by evaporating, it cools the body, protecting it from overheating.

Water and mineral salts create mainly the internal environment of the body, being the main component of blood plasma, lymph and tissue fluid. Some salts dissolved in the liquid part of the blood are involved in the transport of gases by the blood.

Water and mineral salts are part of the digestive juices, which determines their importance for the digestive process. And although neither water nor mineral salts are sources of energy in the body, their normal intake and removal from the body is a condition for its normal activity. Water in an adult is approximately 65% ​​of body weight, in children - about 80%.

Loss of water by the body leads to very severe disorders. For example, in case of indigestion in infants, dehydration of the body is a great danger, this entails convulsions, loss of consciousness. Depriving a person of water for several days is fatal.

Water exchange. The body is constantly replenished with water by absorbing it from the digestive tract. A person needs 2-2,5 liters of water per day with a normal diet and normal ambient temperature. This amount of water comes from the following sources: water consumed when drinking (about 1 l); water contained in food (about 1 l); water, which is formed in the body during the metabolism of proteins, fats and carbohydrates (300-350 cubic cm).

The main organs that remove water from the body are the kidneys, sweat glands, lungs and intestines. The kidneys remove 1,2-1,5 liters of water from the body per day as part of the urine. Sweat glands remove 500-700 cubic meters of water through the skin in the form of sweat. cm of water per day. At normal temperature and humidity per 1 sq. cm of the skin, about 10 mg of water is released every 1 minutes. Light in the form of water vapor displays 350 cubic meters. see water; this amount increases sharply with deepening and quickening of breathing, and then 700-800 cubic meters can stand out per day. see water. Through the intestines with feces, 100-150 cubic meters are excreted per day. see water; with a disorder of the intestines, more water can be excreted, which leads to depletion of the body with water.

For the normal functioning of the body, it is important that the flow of water into the body completely covers its consumption. If more water is excreted from the body than it enters, there is a feeling of thirst. The ratio of the amount of water consumed to the amount allocated is the water balance.

In the body of a child, extracellular water predominates, which leads to a greater hydrolability of children, that is, the ability to quickly lose and quickly accumulate water. The need for water per 1 kg of body weight decreases with age, and its absolute amount increases. A three-month-old child needs 150-170 g of water per 1 kg of body weight, at 2 years old - 95 g, at 12-13 years old - 45 g. The daily water requirement for a one-year-old child is 800 ml, at 4 years old - 950-1000 ml, -5 years old - 6 ml, at 1200-7 years old - 10 ml, at 1350-11 years old - 14 ml.

The importance of mineral salts in the process of child growth and development. The presence of minerals is associated with the phenomenon of excitability and conductivity in the nervous system. Mineral salts provide a number of vital functions of the body, such as the growth and development of bones, nerve elements, muscles; determine the blood reaction (pH), contribute to the normal functioning of the heart and nervous system; used for the formation of hemoglobin (iron), hydrochloric acid of gastric juice (chlorine); maintain a certain osmotic pressure.

In a newborn, minerals make up 2,55% of body weight, in an adult - 5%. With a mixed diet, an adult receives all the minerals he needs in sufficient quantities with food, and only table salt is added to human food during its culinary processing. A growing child's body especially needs an additional intake of many minerals.

Minerals have an important influence on the development of the child. Bone growth, the timing of cartilage ossification, and the state of oxidative processes in the body are associated with calcium and phosphorus metabolism. Calcium affects the excitability of the nervous system, muscle contractility, blood clotting, protein and fat metabolism in the body. Phosphorus is needed not only for the growth of bone tissue, but also for the normal functioning of the nervous system, most glandular and other organs. Iron is part of the hemoglobin in the blood.

The greatest need for calcium is noted in the first year of a child's life; at this age it is eight times greater than in the second year of life, and 13 times greater than in the third year; then the need for calcium decreases, increasing slightly during puberty. Schoolchildren have a daily requirement for calcium - 0,68-2,36 g, for phosphorus - 1,5-4,0 g. The optimal ratio between the concentration of calcium and phosphorus salts for preschool children is 1: 1, at the age of 8-10 years - 1: 1,5, in adolescents and older students - 1: 2. With such relationships, the development of the skeleton proceeds normally. Milk has an ideal ratio of calcium and phosphorus salts, so the inclusion of milk in the diet of children is mandatory.

The need for iron in children is higher than in adults: 1-1,2 mg per 1 kg of weight per day (in adults - 0,9 mg). Sodium children should receive 25-40 mg per day, potassium - 12-30 mg, chlorine - 12-15 mg.

Vitamins. These are organic compounds that are absolutely necessary for the normal functioning of the body. Vitamins are part of many enzymes, which explains the important role of vitamins in metabolism. Vitamins contribute to the action of hormones, increasing the body's resistance to adverse environmental influences (infections, high and low temperatures, etc.). They are necessary to stimulate growth, tissue and cell restoration after injury and surgery.

Unlike enzymes and hormones, most vitamins are not formed in the human body. Their main source is vegetables, fruits and berries. Vitamins are also found in milk, meat, and fish. Vitamins are required in very small amounts, but their deficiency or absence in food disrupts the formation of the corresponding enzymes, which leads to diseases - beriberi.

All vitamins are divided into two large groups:

a) soluble in water;

b) soluble in fats. Water-soluble vitamins include the group of vitamins B, vitamins C and P. Fat-soluble vitamins include vitamins A1 and A2, D, E, K.

Vitamin B1 (thiamine, aneurin) is found in hazelnuts, brown rice, wholemeal bread, barley and oatmeal, especially in brewer's yeast and liver. The daily requirement for a vitamin is 7 mg for children under 1 years old, 7 mg from 14 to 1,5 years old, 14 mg from 2 years old, and 2-3 mg for adults.

In the absence of vitamin B1 in food, beriberi develops. The patient loses his appetite, quickly gets tired, gradually there is weakness in the muscles of the legs. Then there is a loss of sensitivity in the muscles of the legs, damage to the auditory and optic nerves, cells of the medulla oblongata and spinal cord die, paralysis of the limbs occurs, and without timely treatment - death.

Vitamin B2 (riboflavin). In humans, the first sign of a lack of this vitamin is a skin lesion (most often in the lip area). Cracks appear, which become wet and covered with a dark crust. Later, damage to the eyes and skin develops, accompanied by the falling off of keratinized scales. In the future, malignant anemia, damage to the nervous system, a sudden drop in blood pressure, convulsions, and loss of consciousness may develop.

Vitamin B2 is contained in bread, buckwheat, milk, eggs, liver, meat, tomatoes. The daily requirement for it is 2-4 mg.

Vitamin PP (nicotinamide) is found in green vegetables, carrots, potatoes, peas, yeast, buckwheat, rye and wheat bread, milk, meat, and liver. The daily requirement for it in children is 15 mg, in adults - 15-25 mg.

With beriberi PP, there is a burning sensation in the mouth, profuse salivation and diarrhea. The tongue becomes crimson red. Red spots appear on the arms, neck, face. The skin becomes rough and rough, which is why the disease is called pellagra (from the Italian pelle agra - rough skin). With a severe course of the disease, memory weakens, psychoses and hallucinations develop.

Vitamin B12 (cyanocobalamin) in humans is synthesized in the intestines. Contained in the kidneys, liver of mammals and fish. With its deficiency in the body, malignant anemia develops, associated with a violation of the formation of red blood cells.

Vitamin C (ascorbic acid) is widely distributed in nature in vegetables, fruits, needles, and in the liver. Ascorbic acid is well preserved in sauerkraut. 100 g of needles contain 250 mg of vitamin C, 100 g of rose hips - 150 mg. The need for vitamin C is 50-100 mg per day.

Vitamin C deficiency causes scurvy. Usually the disease begins with general malaise, depression. The skin acquires a dirty gray tint, the gums bleed, the teeth fall out. Dark spots of hemorrhages appear on the body, some of them ulcerate and cause sharp pain.

Vitamin A (retinol, axerophthol) in the human body is formed from the widespread natural pigment carotene, which is found in large quantities in fresh carrots, tomatoes, lettuce, apricots, fish oil, butter, liver, kidneys, egg yolk. The daily requirement for vitamin A in children is 1 mg, adults - 2 mg.

With a lack of vitamin A, the growth of children slows down, "night blindness" develops, that is, a sharp drop in visual acuity in dim lighting, leading in severe cases to complete but reversible blindness.

Vitamin D (ergocalciferol) is especially necessary for children to prevent one of the most common childhood diseases - rickets. With rickets, the process of bone formation is disrupted, the bones of the skull become soft and pliable, the limbs are bent. On the softened parts of the skull, hypertrophied parietal and frontal tubercles are formed. Sluggish, pale, with an unnaturally large head and a short bow-legged body, a large belly, such children lag behind in development.

All these serious violations are associated with the absence or deficiency of vitamin D in the body, which is found in yolks, cow's milk, and fish oil.

Vitamin D can be formed in human skin from provitamin ergosterol under the influence of ultraviolet rays. Fish oil, sun exposure or artificial ultraviolet irradiation are the means of preventing and treating rickets.

10.3. Age features of energy metabolism

Even in conditions of complete rest, a person consumes a certain amount of energy: energy is continuously spent in the body on physiological processes that do not stop for a minute. The minimum level of metabolism and energy expenditure for the body is called the basic metabolism. The main metabolism is determined in a person in a state of muscle rest - lying down, on an empty stomach, i.e. 12-16 hours after eating, at an ambient temperature of 18-20 ° C (comfort temperature). In a middle-aged person, the basal metabolism is 4187 J per 1 kg of mass per hour. On average, this is 7-140 J per day. For each individual, the basal metabolic rate is relatively constant.

Features of basal metabolism in children. Since children have a relatively larger body surface per unit mass than an adult, their basal metabolism is more intense than that of adults. In children there is also a significant predominance of assimilation processes over dissimilation processes. The younger the child, the higher the energy costs for growth. Thus, energy expenditure associated with growth at the age of 3 months is 36%, at the age of 6 months - 26%, and at 9 months - 21% of the total energy value of food.

The basal metabolism per 1 kg of mass in an adult is 96 J. Thus, in children 600-8 years old, the basal metabolism is two or two and a half times higher than in adults.

The basal metabolic rate in girls is somewhat lower than in boys. This difference begins to appear already in the second half of the first year of life. The work performed in boys entails a higher energy expenditure than in girls.

Determining the basal metabolic rate often has diagnostic value. The basal metabolism increases with excessive thyroid function and some other diseases. With insufficiency of the function of the thyroid gland, pituitary gland, gonads, the basal metabolism decreases.

Energy expenditure during muscle activity. The harder the muscular work, the more energy a person spends. For schoolchildren, preparing for a lesson and a lesson at school require energy 20-50% higher than the basal metabolic energy.

When walking, energy costs are 150-170% higher than the main metabolism. When running, climbing stairs, energy costs exceed the basic metabolism by 3-4 times.

Training the body significantly reduces the energy consumption for the work performed. This is due to a decrease in the number of muscles involved in the work, as well as a change in breathing and blood circulation.

People of different professions have different energy expenditures. With mental labor, energy costs are lower than with physical labor. Boys have a higher total daily energy expenditure than girls.

Author: Antonova O.A.

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