Metabolism and its features in children of different age groups. Symptoms of metabolic disorders in children Visible signs of slow body functioning

The main stages of metabolism and energy in children from birth to the formation of an adult organism have a number of their own characteristics. At the same time, quantitative characteristics change, and a qualitative restructuring of metabolic processes occurs. Thus, in children, unlike adults, a significant part of the energy is spent on plastic processes, which are greatest in young children.

The basal metabolic rate in children varies depending on the child's age and type of diet. In the first days of life it is 512 kcal/m2, then gradually increases and by 1.5 years it has a value of 1200 kcal/m2. By the period, energy consumption for basal metabolism decreases to 960 kcal/m2. At the same time, boys have higher energy costs for basal metabolism per 1 kg of body weight than girls. With growth, energy expenditure on muscle activity increases.

The main reason, which largely determines the state of metabolic processes in childhood, is the incomplete development of humoral and nervous regulatory mechanisms, which ensure the body’s adaptation to the influence of the external environment and a more uniform nature of responses. An expression of the immaturity of regulatory mechanisms is, for example, the insufficient ability of the liver and kidneys to detoxify and cleanse the body of various harmful products, as well as significant fluctuations in the osmotic pressure of blood plasma, a tendency to hyperkalemia, etc.

From the second week of life, the processes of anabolism over catabolism begin to predominate in the child. Protein metabolism is characterized by a positive nitrogen balance and an increased need for protein. A child needs 4-7 times more amino acids than an adult. The child also has a greater need for carbohydrates; At their expense, caloric needs are mainly covered. Metabolism is closely related to nitrogen metabolism. Glucose contributes to protein, its administration reduces the concentration of amino acids in the blood. Reaction energy is required to fully utilize fat. Fat makes up about 1/8 of a child's body and is a carrier of energy, promotes the absorption of fat-soluble vitamins, protects the body from cooling, and is a structural part of many tissues. Certain unsaturated fatty acids (see Fats) are essential for the growth and normal function of the skin. At birth, the content of lipids (see) in the child’s blood is reduced, and the content of phosphatides is significantly lower than. In addition, children have a physiological tendency toward ketosis, in which low glycogen reserves may play a role.

The water content in a child's tissues is high and amounts to 3/4 of body weight in infants and decreases with age. There are regular daily fluctuations in water release. In a healthy infant, it increases in the afternoon, reaching a maximum at midnight, and decreases sharply in the morning. Therefore, weighing the child is more reasonable in the morning, which gives a correct idea of ​​the true weight gain.

The processes of metabolism and energy are especially intense during the growth and development of children and adolescents, which is one of the characteristic features of a growing organism. At this stage of ontogenesis, plastic processes significantly prevail over destruction processes, and only in an adult a dynamic balance is established between these processes of metabolism and energy. Thus, in childhood the processes of growth and development or assimilation predominate, in old age - the processes of dissimilation. This pattern can be disrupted as a result of various diseases and other extreme environmental factors.

Cells contain about 70 chemical elements that form two main types of chemical compounds in the body: organic and inorganic substances. The body of a healthy adult of average weight (70 kg) contains approximately: water - 40-45; proteins – 15-17; fats – 7-10; mineral salts – 2.5-3; carbohydrates – 0.5-0.8. The continuous processes of synthesis and decomposition occurring in the body require a regular supply of material necessary to replace the already obsolete particles of the body. This “building material” enters the body with food. The amount of food that a person eats during his life is many times greater than his own weight. All this indicates the high speed of metabolic processes in the human body.

Protein metabolism. Proteins make up about 25% of total body weight. This is the most difficult part of it. Proteins are polymer compounds made up of amino acids. The protein set of each person is strictly unique and specific. In the body, food protein, under the influence of digestive juices, is broken down into its simple components - peptides and amino acids, which are then absorbed in the intestines and enter the blood. Of the 20 amino acids, only 8 are essential for humans. These include: tryptophan, leucine, isoleucine, valine, threonine, lysine, methionine and phenylalanine. Histidine is also necessary for a growing organism.

The absence of any of the essential amino acids in food causes serious disruptions to the functioning of the body, especially a growing one. Protein starvation leads to a delay and then to a complete cessation of growth and physical development. The child becomes lethargic, there is a sharp loss of weight, profuse swelling, diarrhea, inflammation of the skin, anemia, a decrease in the body's resistance to infectious diseases, etc. This is explained by the fact that protein is the main plastic material of the body, from which various cellular structures are formed. In addition, proteins are part of enzymes, hormones, nucleoproteins, form hemoglobin and blood antibodies.

If the work is not associated with intense physical activity, the human body on average needs approximately 1.1-1.3 g of protein per 1 kg of body weight per day. As physical activity increases, the body's need for protein also increases. For a growing body, protein needs are much higher. In the first year of postnatal development, a child should receive more than 4 g of protein per 1 kg of body weight, at 2-3 years - 4 g, at 3-5 years - 3.8 g, etc.

Metabolism of fats and carbohydrates. These organic substances have a simpler structure; they consist of three chemical elements: carbon, oxygen and hydrogen. The same chemical composition of fats and carbohydrates allows the body, when there is an excess of carbohydrates, to build fats from them, and, conversely, if necessary, carbohydrates are easily formed from fats in the body.

The total amount of fat in the human body is on average about 10-20%, and carbohydrates - 1%. Most of the fat is found in adipose tissue and forms a reserve energy reserve. A minority of fats is used to build new cell membrane structures and replace old ones. Some cells of the body are capable of accumulating fat in huge quantities, acting as thermal and mechanical insulation in the body.

Fats should make up about 30% of a healthy adult's diet. total calorie content of food, i.e. 80-100 g per day. It is necessary to use fats of both animal and vegetable origin in food in a 2:1 ratio, since some components of vegetable fats cannot be synthesized in the body. These are the so-called unsaturated fatty acids: linoleic, linolenic and arachidonic. Insufficient intake of these fatty acids into the human body leads to metabolic disorders and the development of atherosclerotic processes in the cardiovascular system.

The fat needs of children and adolescents have their own age-related characteristics. So, until 1.5 years of age there is no need for vegetable fats, and the total need is 50 g per day, from 2 to 10 years the need for fats increases 80 g per day, and for vegetable fats - up to 15 g, during puberty the need for fat intake for boys is 110 g per day, and for girls - 90 g, and the need for vegetable fats is the same for both sexes - 20 g per day.

Carbohydrates in the body are broken down into glucose, fructose, galactose, etc. and then absorbed into the blood. Glucose content in the blood of an adult is constant and equals on average 0.1%. When the amount of sugar in the blood increases to 0.11-0.12%, glucose moves from the blood to the liver and muscle tissue, where it is stored in the form of animal starch - glycogen. With a further increase in blood sugar to 0.17%, the kidneys are involved in its removal from the body, and sugar appears in the urine. This phenomenon is called glucosuria .

The body uses carbohydrates mainly as energy material. Under normal conditions, on average, an adult man engaged in mental or light physical labor requires 400-500 g of carbohydrates per day. The carbohydrate needs of children and adolescents are significantly lower, especially in the first years of life. Thus, up to 1 year, the need for carbohydrates is 110 g per day, from 1.5 to 2 years - 190 g, at 5-6 years - 250 g, at 11-13 years - 380 g and in boys - 420 g, and for girls - 370 g. In the children's body, there is a more complete and rapid absorption of carbohydrates and greater resistance to excess sugar in the blood.

Water-salt exchange. Water for the life of the body plays a much larger role than other components of food. The fact is that water in the human body is simultaneously a building material, a catalyst for all metabolic processes and a thermostat of the body. The total amount of water in the body depends on age, gender and weight. On average, a man's body contains over 60% water, a woman's body contains 50%.

The water content in a child's body is much higher, especially in the first stages of development. According to embryologists, the water content in the body of a 4-month fetus reaches 90%, and in a 7-month fetus – 84%. In a newborn's body, the volume of water ranges from 70 to 80%. In postnatal ontogenesis, the water content decreases rapidly. So, the child is 8 months old. the water content is 60%, for a 4.5-year-old child - 58%, for 13-year-old boys - 59%, and for girls of the same age - 56%. The higher water content in children's bodies is obviously associated with a greater intensity of metabolic reactions associated with their rapid growth and development. The overall water requirement of children and adolescents increases as the body grows. If a one-year-old child needs approximately 800 ml of water per day, then at 4 years old - 1000 ml, at 7-10 years old - 1350 ml, and at 11-14 years old - 1500 ml.

Mineral metabolism. The role of microelements comes down to the fact that they are subtle regulators of metabolic processes. By combining with proteins, many microelements serve as material for the construction of enzymes, hormones and vitamins.

The needs of an adult and a child for minerals are significantly different; a lack of minerals in a child’s food more quickly leads to various metabolic disorders and, accordingly, to impaired growth and development of the body. Thus, the norm of calcium intake in the body of a one-year-old child is 1000 mg per day, phosphorus – 1500 mg. At the age of 7 to 10 years, the need for microelements increases, calcium is required 1200 mg per day, phosphorus - 2000 mg. By the end of puberty, the need for microelements decreases slightly.

Vitamins. Our body requires them in negligible quantities, but their absence leads the body to death, and lack of nutrition or disruption of their absorption processes leads to the development of various diseases called hypovitaminosis.

About 30 vitamins are known that affect various aspects of metabolism, both individual cells and the entire organism as a whole. This is due to the fact that many vitamins are part of enzymes. Consequently, the lack of vitamins causes a cessation of enzyme synthesis and, accordingly, metabolic disorders.

A person receives vitamins from food of plant and animal origin. For normal life, a person needs 16-18 of 30 vitamins. Vitamins B 1, B 2, B 12, PP, C, A and D are especially important. Up to one year, the norm for vitamin A is 0.5 mg, B 1 - 0.5 mg, B 2 - 1 mg, PP – 5 mg, B 6 – 0.5 mg, C – 30 mg and D – 0.15 mg. In the period from 3 to 7 years, the norm for vitamin A is 1 mg, B 1 - 1.5 mg, B 2 - 2.5 mg, PP - 10 mg, B 6 - 1.5 mg, C - 50 mg, and The need for vitamin D remains the same – 0.15 mg. At the time of puberty, the normal requirement for vitamin A is 1.5 mg, B 1 - 2 mg, B 2 - 3 mg, PP - 20 mg, B 6 - 2 mg, C - 70 mg and D - 0.15 mg.

A growing body is highly sensitive to a lack of vitamins in food. The most common hypovitaminosis among children is a disease called rickets. It develops when there is a lack of vitamin D in baby food and is accompanied by impaired skeletal formation. Rickets occurs in children under 5 years of age.

It should also be noted that the intake of excess amounts of vitamins into the body can cause serious disturbances in its functional activity and even lead to the development of diseases called hypervitaminosis. Therefore, you should not abuse vitamin preparations and include them in your diet only on the recommendation of a doctor.

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Subject, tasks of age-related physiology and its connection with other sciences
Age-related physiology is a science that studies the features of the life processes of an organism at different stages of ontogenesis. It is an independent branch of physiology

History and main stages in the development of age-related physiology
The scientific study of the age-related characteristics of the child’s body began relatively recently - in the second half of the 19th century. Soon after the discovery of the law of conservation of energy, physiologists discovered that children

Research methods in developmental physiology
Science is complete if its methodological arsenal corresponds to the problems that it has to solve. For age-related physiology, the most important task is to study the dynamics and patterns

Growth and development of the body of children and adolescents
Growth is an increase in the length, volume and weight of the body of children and adolescents. Growth is carried out due to the processes of hyperplasia - an increase in the number of cells and the number of their components

Heredity and development of the body
Heredity is the ability of living organisms to accumulate, store and transmit hereditary information to offspring. The transmission and storage of hereditary characteristics ensures

Acceleration and retardation of development
Acceleration refers to the acceleration of the growth and development of children and adolescents, as well as the absolute increase in the body size of adults. This term was proposed by E. Koch (19

Sensitive periods of development of children and adolescents
In the process of individual development, there are critical periods when the sensitivity of the developing organism to the effects of damaging factors of the external and internal environment is increased. Not allocated

Development of the central nervous system during ontogenesis
The nervous system coordinates and regulates the activity of all organs and systems, ensuring the functioning of the body as a whole; carries out adaptation of the body to changes in the environment

The main stages of development of higher nervous activity
The lower and higher nervous activity of the child is formed as a result of the morphofunctional maturation of the entire nervous system. The nervous system, and with it higher nervous activity in children

Age-related characteristics of psychophysiological functions
perception. It plays a vital role in ensuring contacts with the external environment and in the formation of cognitive activity. Perception is a complex active process

Features of sensory function in children and adolescents
Elementary reflex activity of a person, his complex behavioral acts and mental processes depend on the functional state of his sense organs: vision, hearing, smell, taste, somatic

Age-related features of the visual sensory system
After birth, the human visual organs undergo significant morphofunctional changes. For example, the length of the eyeball in a newborn is 16 mm, and its weight is 3.0 g; by the age of 20, these

Age-related characteristics of the auditory sensory system
already at 8-9 months of intrauterine development, the child perceives sounds within the range of 20-5000 Hz and reacts to them with movements. A clear reaction to sound appears in a child at 7-8 weeks after birth, and

Age-related characteristics of other sensory systems
The vestibular sensory system plays an important role in regulating the position of the body in space and its movements. The development of the vestibular apparatus in children and adolescents is currently

Concept of hormones and endocrine system
The most ancient form of regulation of functions were chemical substances secreted by cells. Examples include substances such as nerve growth factor and epidermal growth factor. However, the action

Formation of endocrine function in ontogenesis
Most hormones begin to be synthesized in the 2nd month of intrauterine development, but hormones such as vasopressin and oxytocin are found in the endocrine glands of the fetus at 4-5 months.

The influence of hormones on body growth
Growth processes in the body are determined by the action of a number of hormonal factors. The main one is somatotropin - a hormone of the anterior pituitary gland. Under its influence, new formation occurs

The role of hormones in the body's adaptation to physical activity
Hormones play a vital role in the body’s adaptation to physical stress. In the ensemble of endocrine glands, the sympathoadrenal and pituitary-adrenal glands are the first to respond to muscle load.

Age-related features of blood quantity and composition
The amount of blood in the human body changes with age. Children have more blood relative to their body weight than adults. In newborns, blood makes up 14.7% of the mass, in children of one year - 10.9%,

The heart and its age-related features
The heart is a hollow muscular organ located on the left side of the chest. The formation of the heart in the embryo begins from the 2nd week of prenatal development, and its development

Age-related features of the circulatory system
Another important indicator of the cardiovascular system is blood pressure. It represents the variable pressure under which the blood is in the circulatory system

Age-related characteristics of the cardiovascular system’s response to physical activity
As the cardiovascular system grows and develops, its response to physical activity in children and adolescents also changes. The age-related characteristics of these reactions are clearly manifested both when staging

Development of the respiratory organs in ontogenesis
The lungs and airways begin to develop in the embryo at the 3rd week from the mesodermal mesenchyme. Subsequently, in the process of growth, the lobar structure of the lungs is formed; after 6 months,

Age-related features of the digestive organs
The most significant morphological and functional differences between the digestive organs of an adult and a child are observed only in the first years of postnatal development. Functional asset

Energy metabolism in children and adolescents
Metabolism in the body is closely related to the transformation of energy. The amount of energy produced in the body can be determined using direct and indirect calorimetry. One of the most important indicators

Skeleton and its age features
The formation of the skeleton occurs in the 3rd week of embryonic development: initially as a connective tissue formation, and in the middle of the 2nd month of development it is replaced by cartilage, after which

Development of the muscular system
Muscle development begins in the 3rd week. Almost all striated muscles originate from myotomes. In a 4-week embryo, myotomes consist of mononuclear round cells, later - from

Age-related characteristics of motor skills and movement coordination
A newborn baby exhibits erratic movements of the limbs, torso and head. Coordinated rhythmic flexion, extension, adduction and abduction are replaced by arrhythmic, isolated ones

Musculoskeletal disorders
Posture. The habitual position of a person’s body while walking, standing, sitting and working is called posture. Correct posture is characterized by the normal position of the spine with its

Control questions.

1. Describe the functional system: mother’s body - placenta - fetus. Factors influencing fetal development: genetic, health, nutrition, working conditions of the mother.

2. Newborn baby. Anatomical and functional signs of term and prematurity. Causes of prematurity and stillbirth. Stillbirth rate.

3. Features of the period of early adaptation of the newborn. The concept of “intrauterine” malnutrition, its causes. Features of the course of physiological conditions of newborns: physiological loss of body weight, physiological catarrh of the skin, conjugation jaundice, sexual crisis.

4. The main forms of pathology of newborns: hemolytic disease of the newborn, hyaline membrane disease, intrauterine growth and development retardation (IUGR), intrauterine infections.

5. What are the patterns of growth and body weight of children in the first year of life. Functional characteristics of the infancy period and the nature of the pathology.

6. The period of pre-preschool childhood. Its characteristics and features of pathology. Preschool and school periods of childhood.

References.

1. Physiology of growth and development of children and adolescents (theoretical and clinical issues). In 2 volumes. Ed. A.A. Baranova, L.A. Shcheplyagina, ed. "GEOTAR-Media", 2006, 896 p.

2. Guidelines from a local pediatrician. Ed. T.G. Avdeeva, ed. "GEOTAR-Media", 2008, 352 p.

3. Fedko N.A. - Modern pediatrics: Textbook - (Medicine for you) / Phoenix, 2007 384 pp.

4. Lazareva G.Yu. Pediatrics: lecture notes. Ed. "Phoenix", 2008, 326 p.

Protein metabolism. In the child’s body there is a pronounced predominance of anabolic processes aimed at ensuring its growth and development. In this regard, proteins, whose main function is plastic, are of particular importance for children. Amino acids formed during the breakdown of food proteins are used for the synthesis of tissue proteins, enzymes, biologically active substances, hormones, and mediators. Proteins are characterized by supporting, contractile, transport, protective, regulatory, and energy functions. In terms of the content of essential amino acids, breast milk proteins are the best absorbed for infants. Child's protein needs averages 2.5-4 g per 1 kg of weight, while in an adult it is much less and does not exceed 1-1.5 g per 1 kg of weight. To ensure normal growth and development, a child needs to receive proteins from food that include all the essential amino acids. The diet of a child under 3 years old should include at least 75% complete proteins, from 3 to 7 years old - 60% and from 7 to 14 years old - 50%. The criterion for the health of a growing organism is a positive nitrogen balance, The younger the child is, the more pronounced nitrogen retention is. Its high level corresponds to a high degree of protein absorption in the gastrointestinal tract in children. When breastfeeding Some albumins and globulins in milk are absorbed from the intestine without being broken down first. As a result, antibodies and antitoxins enter the body of children in the first months of life. The digestion of proteins in the stomach begins under the influence of pepsin. Due to the low acidity of gastric juice, its activity in infants is low. As a result of the action of proteolytic enzymes of the stomach, peptones, simple polypeptides, are formed. They enter the intestine, where, exposed to the influence of proteases of the pancreas and intestines - trypsin, chymotrypsin, carboxypeptidase, amino-, dipeptidases, they are broken down into free amino acids, which are absorbed through the wall of the small intestine and enter the blood. For young children characterized by increased permeability of the intestinal wall to proteins and their breakdown products, low activity of intestinal proteolytic enzymes, and the absence of putrefaction in the large intestine. The synthesis of body-specific proteins is under the control of DNA, which is part of the cell nucleus. In childhood, biosynthesis proceeds at a much higher rate and is sensitive to the effects of mutagenic factors. Protein formation in the body is an energy-dependent process. The main suppliers of macroergs in childhood are anaerobic glycolysis and glycogenolysis, the energy effect of which is much lower than that of aerobic glycolysis. Therefore, children are especially susceptible to carbohydrate deficiency, as this inhibits the process of protein synthesis, resulting in decreased body weight and stunted growth. In the first 6 months of life, the content of plasma proteins in children is lower than in adults. In newborns, urinary excretion of amino acids is increased. In the first months of life, ethanolamine, homocitrulline, proline, and hydroxyproline are also determined in the urine. This so-called physiological hyperaminoaciduria indicates the incomplete development of the renal tubular transport systems for amino acids in early childhood. Transamination processes in children are more intense than in adults, as evidenced by the high activity of ACAT and ALAT in the blood serum, especially in newborns. In this regard, in childhood there is a greater need for vitamin B6 (pyridoxine). The process of formation of urea and uric acid in a child is subject to significant age-related fluctuations. In children it occurs less intensely than in adults, due to the low activity of the enzymes involved in its synthesis. The peculiarity of protein metabolism in children it manifests itself in different quantitative ratios than in adults, the products of nitrogen metabolism excreted in the urine. Fetal urine contains only traces of urea and excess uric acid, which is accompanied by deposition of the latter in the kidney tissue and the development of “uric acid infarction” in newborns. The first 3 months of life are characterized by the highest excretion of uric acid and relatively low excretion of urea. In childhood, the nitrogen content is significantly lower. Daily nitrogen excretion in newborns is in the range of 0.3-0.5g (in adults it is 10-18g per day) with age it increases and by 10-14 years it reaches 9-10g. Physiological creatinuria is observed in children: in boys - up to 10 years, in girls - up to 12-16 years. Only traces of creatine are found in the urine of adults. The percentage of creatine nitrogen to urine nitrogen in the first days of life is 0.7-0.8, by the year - 0.3-0.4, which is associated with insufficiency of enzymatic systems in the muscles that carry out its metabolism. Creatine is converted into creatinine only to a small extent and, remaining unused, leads to creatinuria. Daily excretion of the latter in urine increases with age. The urine of healthy children also contains traces of indican. Its quantity increases with the intensification of putrefactive processes in the intestines. All children are characterized by a positive nitrogen balance - a necessary condition for growth: the highest digestibility of nitrogen in the body is observed in the first months of life, then it gradually decreases and in children 2-3 years old it is 30%, 4-6 years old - 25%, 7- 8 years - 21%, 11-13 years - 13.8%. Lipid metabolism. A growing body needs mainly animal fats contained in milk, butter, and egg yolks. However, vegetable fats should also be included in the child’s diet; it is best if they make up 10-15% of the total fat. The younger the child is, the higher his need for fats. So, in infants it is equal to 5-7 g per 1 kg of body weight, in 3-4 year olds - 3.5-4 g, in children of preschool and school age - about 2.5-3 g per 1 kg of body weight per day. It is important that the ratio between fats and carbohydrates in food is 1:2. In infants, the digestion of fats begins in the stomach under the influence of lipase, activated by lipolytic enzymes of mother's milk; in the process of growth, pancreatic juice lipase and bile acids become dominant, the amount of which increases with age.

Increased permeability of the intestinal wall in children promotes faster absorption of fat hydrolysis products. About 5% of dietary fats in adults are excreted in feces; in children, the amount of undigested fats is slightly higher - on average 6-10%. In a child, a significant part of the fat is deposited in the subcutaneous tissue and peritoneum. The predominance of the processes of its deposition over its use is combined in young children with easy depletion of fat depots, which is largely explained by the imperfection of neurohumoral regulatory mechanisms. During the newborn period plays a special role brown adipose tissue, which is characterized by a response to adrenaline and the mobilization of NEFA. It is a kind of heat regulation organ, where free oxidation of fatty acids occurs with the release of heat. In the adipose tissue of children of all ages, there is more intense oxidation of fatty acids than in adults, active inclusion of glucose in the biosynthesis of fatty acids and triglycerides, and a higher concentration of coenzyme A. With natural feeding, the blood cholesterol content is 10-15% higher than with breastfeeding cow's milk. In the blood, cholesterol is found both in a free state and in combination with fatty acids. If in a newborn the share of free cholesterol accounts for 65%, then by the end of the first day the ratio between these forms levels out, and then begins to shift towards the predominance of the ester-bound form with an increase in total cholesterol in the blood serum. The nature of nutrition is of no small importance in the regulation of fat metabolism. Long-term excess consumption of fats and carbohydrates leads to increased fat deposition.

Peculiarities of childhood are instability and lability of lipid metabolism, increased lipolytic activity of adipose tissue to adrenaline and glucagon, which leads to rapid mobilization of lipids from fat depots and their depletion, as evidenced by higher NEFA numbers in the blood serum of young children. The quantitative ratio of lipid classes in blood serum to a certain extent reflects the state of lipid metabolism in children of different ages. In general, the early periods of child development are characterized by lower lipid levels and relatively low activity of lipolytic enzymes in the blood serum. In children under 7-10 years of age, there is an increased tendency to ketosis. Hyperketonemia and ketouria can develop under the influence of short-term hunger, overwork, overeating, infections, and stress. This is due to the instability of carbohydrate metabolism, low glycogen reserves, peculiarities of ketogenic amino acid metabolism, slow oxidation of ketone bodies in tissues and their removal from the body. Carbohydrate metabolism. Carbohydrates refer to polyhydric alcohols containing aldehyde and ketone groups. They are the main source of energy for both adults and children. When 1 g of carbohydrates is oxidized, 3.75 kcal is released, which can be accumulated in ATP or released as heat. Carbohydrates perform a plastic function, being part of many structures of the body: nucleic acids, cell membranes, the main substance of connective tissue, etc., and can also be a nutrition reserve. The biological polymer of glucose - glycogen, with proper nutrition, accumulates in the liver (up to 10%) and in skeletal muscles (up to 2%). In combination with proteins, carbohydrates affect the permeability of cell membranes, the conduction of nerve impulses, the formation of antibodies, determine the specificity of blood groups, and the individual characteristics of tissues. Carbohydrate components are part of a number of hormones, vitamins, coenzymes, and are involved in the processes of blood clotting, regeneration, etc. The need for carbohydrates in a growing body is very significant. In infancy, it is 10-12 g per 1 kg of body weight per day, and in older age - 12-15 g. An infant receives 40% of calories from the oxidation of carbohydrates, and 50% from breakdown. With age, this ratio gradually changes, and an adult meets 60% of his total energy needs from carbohydrates. Carbohydrates come from food in the form of monosaccharides (glucose, fructose), disaccharides (lactose, sucrose, maltose) and polysaccharides (starch, glycogen). In the first months of life, the main dietary carbohydrate is lactose, consisting of glucose and galactose. Its content in human milk is on average 70 g/l, in cow's milk 48 g/l.

Digestion of carbohydrates begins in the mouth. Under the action of salivary amylase, starch and glycogen are broken down into dextrins and maltose. Amylase in saliva is already detected in the fetus, but its activity at this time is still insignificant. At the age of 3-5 months it begins to gradually increase, reaching a maximum at 1-4 years. By this time, the enzyme maltose, which is absent in infants, is also detected in the child’s saliva. In the stomach, the action of amylase practically stops. In the duodenum, after neutralization of hydrochloric acid with bicarbonates of pancreatic juice, all conditions are created for further hydrolysis of starch residues, dextrins and disaccharides. In the intestines of a child, monosaccharides are absorbed mainly and disaccharides in very small quantities. In children of the first 2 years of life, glucose is resorbed faster than in adults. In infancy and older age, 98-99% of all carbohydrates in food are absorbed. The absorption of glucose and galactose is associated with active transport processes, while the resorption of fructose and pentoses occurs by diffusion. Based on the rate of absorption, carbohydrates can be placed in the following order: galactose, glucose, fructose, mannose. Glucose, already passing through the mucosal cell, can be partially oxidized and used as an energy material, fructose and galactose can be converted into glucose. Carbohydrate metabolism in children is more active than in adults. This is due to the increased use of carbohydrates as energy and plastic material during child growth. In childhood, glucose oxidation in the pentose cycle is highly intense, which ensures increased synthesis of nucleic acids, fatty acids, cholesterol and its derivatives. The growth of a child is closely related to the processes of glycolysis. The younger the child is, the higher they are. The lactic acid formed during them cannot be completely oxidized due to a lack of aerobic processes. As a result, its level in the blood increases, which leads to a shift in the acid-base state towards acidosis. The highest concentration of lactic acid is in newborns (1.9-2.2 mmol/l). With age, it gradually decreases, reaching the adult level by 10 years (0.7 - 1.6 mmol/l). Confirmation of the dominance of glycolytic processes and insufficiency of aerobic processes in newborns is the increased amount of pyruvic acid (up to 227 µmol/l) and the lower content of ATP in tissues. The predominance of glycolytic processes in the early periods of a child’s life is accompanied by high activity of glycolytic enzymes. In the first days of life, newborns experience severe hypoglycemia. 3-6 hours after birth, the content of true glucose is 2.77 ± 1.37 mmol/l, by 5-6 hours its level rises to 3.61 ± 1.1 mmol/l. With age, its content continues to increase and by 14-15 years it reaches adult values ​​(up to 5.55 mmol/l).

In the daily urine of premature newborns, up to 130 mg of carbohydrates are determined, in full-term newborns - up to 80, half of which is lactose. The daily diuresis of infants includes up to 15 mg of glucose, up to 10 mg of galactose, up to 35 mg of lactose, and less than 10 mg of fructose. In children in the first days of life, especially premature ones, galactosuria may be observed. When exposed to oral galactose, newborns develop hyperglycemia, since galactose phosphorylation in the liver is limited in young children. Adults respond to this load by reducing blood glucose levels. To assess the state of carbohydrate metabolism in the clinic, glycemic curves are used after a glucose load. Water-salt exchange. Water is the most important component of a living organism. Its total content in an infant is 70-75%, and in an adult - 60-65% of body weight. Most of the water (40-45% of body weight) is inside the cells, a smaller part (25%) is outside the cells, of which about 20% is interstitial fluid and lymph and 5% is plasma. The total amount of water and its distribution among sectors depends on age. Fluid exchange in the body of children, especially young children, occurs with great intensity and tension. The younger the child, the higher the need for water. So, in a newborn it is 150-200 ml/kg per day, in an infant - 100-150, at 2 years old - 90-95, at 5 years old - 60, at 13 years old - 40 ml/kg body weight per day. Children's need for water is satisfied by drinking liquids and partially dense foods. About 60% of water is excreted from the child’s body by the kidneys, up to 34% by the skin and lungs, and 6% by feces. Excessive water intake is excreted primarily by the kidneys. The exchange of extracellular fluid is especially active. Its intensity in a young child is 2-3 times higher than in an adult, which is associated with high metabolic activity and the large external surface of the child’s body. A child excretes relatively more water through the skin and lungs than an adult. The regulation of water metabolism in children is imperfect; therefore, they may experience rapid disturbances with the formation of edema or the development of exicosis. Regulation of water metabolism is a complex process controlled by the centers of the hypothalamic region. The endocrine glands also participate in it, and above all the pituitary gland, adrenal glands, cerebral appendage and thyroid gland. The state of water metabolism largely depends on the function of the lungs, cardiovascular system, liver and kidneys, and is also closely related to the metabolism of proteins, fats, carbohydrates, vitamins and especially salts. In children 1 year of life, the minimum need for electrolytes is as follows: sodium - 3.5-5.0 mmol; potassium - 7.0-10.0; chlorine - 6.0-8.0; calcium - 2.0-3.0; phosphorus - 1.3-1.7 mmol/day (Yu. E. Veltishchev, 1976). Sodium is the main cation in the extracellular fluid, which also contains relatively high amounts of chlorine and carbonates. Potassium is the main cation of intracellular fluid, where, in addition, the content of magnesium and organic phosphates is increased. Ionic asymmetry is maintained between intracellular and extracellular fluids. There were no significant differences in the ionic composition of interstitial fluid and blood plasma depending on age. The average sodium content in the blood serum of healthy infants is 0.5 mmol/l, potassium is 4.92 mmol/l (M. P. Sheybak, 1980). Sodium maintains the osmotic pressure of the interstitial fluid and plasma, which ensures the relative constancy of their volume. Potassium ensures normal osmotic pressure inside cells, as a result of which the constancy of the intracellular space is maintained, increases the excitability of the neuromuscular system, and promotes the synthesis of glycogen and proteins in cells. Sodium and potassium play an important role in maintaining the acid-base state. Normal blood pH fluctuates within very small limits (7.37-7.44). Its values ​​below 6.8 and above 7.8 are incompatible with life. The constancy of the concentration of hydrogen ions is maintained by buffer systems: bicarbonate, phosphate, protein. The most important is the bicarbonate system of the blood, which includes carbonic acid and its salts - sodium bicarbonate (or potassium bicarbonate. The main source of sodium and chlorine for the body of an older child is table salt added to food, since almost all food products contain relatively small amounts of these elements . The source of potassium is predominantly plant foods, which contain much more of it than in products of animal origin. When artificially feeding cow's milk, a child receives relatively more electrolytes and protein than when breastfeeding. Therefore, given the immaturity of the renal excretory mechanisms in children of 1 year life, when artificially feeding, he needs to be given additional fluid. Calcium is very important for a growing organism, up to 98% of it is concentrated in the bones, where it is associated with phosphates and carbonates, more than 2% is in solution, but in plasma and intercellular fluid. Blood plasma contains 2.5-2.8 mmol/l calcium in three fractions: 1) ionized, 2) in combination with proteins and other colloids, 3) in complex compounds. Almost half of the calcium in the blood plasma is bound to proteins, the other part is ionized calcium, which is more active, amenable to ultrafiltration and freely passes through the walls of the capillaries, as through a dialysing membrane. The most important functions of calcium in the body are maintaining neuromuscular excitability, toning the sympathetic part of the autonomic nervous system, compacting the border zones of cells, participating in blood clotting, building bone tissue, and regulating the acid-base state.

Phosphorus plays an extremely important biological role for a growing organism. About 70% of it is concentrated in bone tissue; it is part of the intercellular fluid and active biochemical compounds of every cell of the body. The blood serum of a child of the 1st year of life contains 1.29-2.26 mmol/l of inorganic phosphorus, children 1-14 years old - 0.62-1.62 mmol/l. Organic phosphorus compounds - ATP, ADP - form the basis of energy metabolism. Phosphorus is necessary for the phosphorylation of carbohydrates and fats, as well as for bone formation. Its inorganic compounds participate in processes aimed at maintaining the acid-base state. The source of phosphorus is food, mainly of animal origin. Sulfur takes part in protein synthesis. It enters the body in the form of inorganic sulfates and with protein compounds, which contain it along with sulfur-containing amino acids.

Iron- the most important element necessary for the synthesis of hemoglobin and a number of tissue enzymes. The content of iron and trace elements in human and cow's milk is insufficient. A child is born with a certain supply of them accumulated in the liver and other organs during intrauterine life. A particularly active intake of iron, copper and other trace elements into the fetus’s body occurs in the last months of pregnancy. In a full-term newborn, iron reserves are 260-300 mg, in premature infants it is much less, and therefore they are more predisposed to iron deficiency anemia.

Copper plays an important role in hemoglobin synthesis and red blood cell maturation. It is associated with the protein ceruloplasmin, which promotes the transition of ferrous iron to ferric iron and the formation of transferrin. Copper deficiency reduces the activity of ceruloplasmin and leads to the development of anemia in infants.

Zinc is necessary for the child for normal growth and development. It is part of the enzyme carbonic anhydrase. The need for zinc in children 1 year of life is 3 mg per day. Milk contains little zinc - up to 0.65 mg/l, much more in colostrum - up to 20 mg/l, zinc deficiency, which is facilitated by chronic diseases of the gastrointestinal tract, occurring with malabsorption syndrome, leads to nutritional disorders and growth retardation .

Vitamins. Intensive metabolism, rapid growth and development of a child are possible only with sufficient intake of vitamins into the body. Currently, about two dozen vitamins are known. They play an important biological role in the activation of plastic processes, being their biocatalysts and material for the synthesis of a number of enzymes or substances that act like hormones. Insufficient intake into the child’s body and disruption of their metabolism leads to the development of hypovitaminosis. All vitamins are usually divided into two groups: 1) fat-soluble (A, E, K) and 2) water-soluble (group B, ascorbic acid, etc.). Substances from which vitamins can be formed in the body are called provitamins. Provitamins, converted into vitamin A in the body are carotenes.

Vitamin A (antixerophthalmic, anti-infective, growth vitamin) is necessary for the synthesis of visual purple (rhodopsin). With a lack of vitamin, the concentration of the latter in the retina of the eyes decreases, as a result of which twilight vision is impaired and night (“night”) blindness develops. Lack of vitamin A inhibits growth, weight gain, and reduces resistance to infections. This vitamin is also necessary for maintaining normal trophic processes in formations of ectodermal origin. If there is a lack of it, dry and flaky skin, brittle nails, dull hair, dry cornea, conjunctiva and other disorders appear. Vitamin A is found mainly in animal fats, and is almost absent in vegetable fats. There is a lot of vitamin A in egg yolk, liver, milk, beef and especially fish oil. Provitamin A is a yellow pigment called carotene - found in carrots and other plants. Under the influence of liver carotinase, carotene in the body is converted into vitamin A. The daily requirement for a child under 1 year of age is 0.5 mg (1600 IU), for children 1-6 years old - 1.0 mg (3300 IU), 7-15 years old - 1.5 mg (5000 IU).

Vitamin D rich in fish oil, egg yolk, liver. Under the influence of ultraviolet rays, it can be synthesized in the skin of children and adults from provitamins (sterol compounds). Excessive administration of vitamin D to a child’s body can cause the phenomenon hypervitaminosis. The latter is more often observed in children born with low birth weight, prematurely born, suffering from malnutrition, who are on artificial and mixed feeding, in cases of increased absorption of calcium in the intestine (idiopathic hypercalcemia), as well as in cases of high individual sensitivity of the child to vitamin D.

Water-soluble B vitamins and vitamin C(ascorbic acid) - active catalysts of redox processes. B vitamins are the basis for the formation of coenzymes that carry out a number of important metabolic reactions. Vitamin B1 (aneurin, thiamine) is part of the enzyme cocarboxylase (thiamine diphosphate), which is used to decarboxylate intermediate products of the breakdown of carbohydrates. With thiamine deficiency, pyruvic and lactic acids accumulate in the body. Necessary for a growing organism as an important factor regulating the activity of the nervous system. With vitamin B deficiency, a typical polyneuritic form of hypovitaminosis develops - beriberi disease, common in countries where mainly polished rice is used in the diet. Vitamin B is found in plant foods. There is especially a lot of it in the germs and shells of cereals (bran), and yeast. The daily requirement for thiamine in the 1st year is 0.5 mg, at an older age - 1.0-2.0 mg.

Metabolic well-being in a child’s body determines the adequacy of its development and maturation. In a mature, adult organism, metabolism is in a state of relatively stable equilibrium with the external environment.

In children, during the process of growth and development, significant changes occur in the morphological characteristics of tissues, their chemical composition and metabolism, therefore the child’s body cannot be considered as a smaller copy of an adult.

The purpose of this review was to summarize and systematize literature data on the biochemical characteristics of the child’s body, which may be useful for pediatricians in understanding some of the patterns of pathogenesis and distinctive features of the symptoms of a number of childhood diseases.

Qualitative and quantitative changes in metabolic processes observed in childhood occur in accordance with the genetic development program and the needs of the child’s body. In this regard, there are a number of features that distinguish the metabolism of a child from an adult.

1. Children are characterized by high tension in certain aspects of metabolism. This primarily concerns rapidly occurring anabolic processes, which include various types of syntheses and high activity of energy metabolism, which provides biosynthetic reactions with ATP energy.

From the moment of fertilization of the egg to the moment of birth of a full-term newborn, the mass increases by 650 million times, and the length of the fetal body during the entire intrauterine period increases by approximately 5 thousand times. This indicates intensive metabolic processes in which anabolic reactions predominate over catabolic ones; in adults, the rates of these two phases of metabolism are equalized.

In connection with the increase in body weight and the development of organs in the body, specific needs for plastic material arise, which determines the high intensity of anabolism. In children, especially in early age periods, the synthesis of proteins occurs at a high rate, which are spent on ensuring the processes of growth, renewal and differentiation of tissues; The synthesis of proteins that perform specific functions in the body (for example, transport of various compounds) is constantly increasing. The synthesis of nucleic acids and the exchange of nitrogenous bases are actively occurring. In particular, uric acid, which characterizes the state of purine metabolism, is formed in children 220 times faster than in adults. Cellular consumption and metabolism of amino acids is intensive, which is caused by their accelerated use in metabolism.

2. Qualitative rearrangements of a number of metabolic pathways depending on the age of the child. During the growth of children, the physical and neuropsychic development of the body, the formation of functional systems and metabolism occur.

The activity of any organ consists of a set of metabolic processes occurring in the cell, and each specific period of a child’s life has its own metabolic characteristics. It is important to emphasize that at each stage of a child’s development there is a metabolic state that provides an optimal ratio of plastic and bioenergetic processes for growth and is most expedient.

Transition to extrauterine existence: metabolic and functional adaptation of the newborn. Active metabolism of lipid components. In the first month of life, anaerobic glycolysis is active in tissues, this ensures increased resistance of the body to hypoxia, but glucose utilization is accompanied by low energy output.

Intensive synthesis of structural proteins for growth, active energy metabolism, increasing role of aerobic glycolysis, active synthesis of functional proteins, transition to nutrition independent of the maternal body, development of functional systems and immunity.

Completion of the myelination processes of the nervous system.

Relative stabilization of metabolism and energy.

3. Increasing the body’s energy reserves during growth (glycogen and fat depot); relative decrease in the volume of extracellular fluid due to an increase in cell mass.

4. Instability (lability) of metabolic processes. It is caused by morphological immaturity and functional inferiority of regulatory mechanisms (CNS, endocrine glands), and is also associated with the immaturity of a number of enzyme systems in the child. In particular, young children have insufficient activity of enzymes that carry out the hydrolytic breakdown of nutrients in the gastrointestinal tract; enzyme reactions associated with tissue respiration; imperfection of the glucuronyltransferase system involved in bilirubin conjugation. A certain role in the instability of a child’s metabolism is also played by the lability of barrier functions (the state of histohematic barriers), which consists in increased permeability of membranes designed to regulate the relative constancy of the composition and properties of cells. All of the above circumstances lead to imperfections in the child’s biochemical adaptation, reduce the body’s reserve capabilities and make it easily vulnerable and highly sensitive to the effects of various unfavorable factors (hypoxia, poor nutrition, infections, etc.). In addition, the lability of the homeostasis system and the imperfection of regulatory mechanisms determine the appearance of peculiar features in the clinic of a particular disease in children compared to the clinical course of the same pathology in adults. The most powerful factor that changes a child’s metabolism is the nature of nutrition, the qualitative and quantitative composition of food consumed. With an irrationally designed diet, it is extremely easy to develop a deficiency of one or another vitamin or other essential nutritional factor.

5. Instability of metabolic processes in childhood manifested by the lability of biochemical parameters (fluctuations in blood glucose, the appearance of sugar in the urine, the ease of proteinuria, the accumulation of ketone bodies, etc.). Healthy children, especially at an early age, are characterized by the influence of food intake on a number of biochemical parameters; in addition, daily fluctuations in biochemical constants in them have a much larger range than in adults. Pathological changes in metabolism occur in a child with particular ease, which is immediately reflected in biochemical parameters. For example, ketosis in children easily develops due to a wide variety of reasons (short-term lack of carbohydrates in food, vomiting, interruption in feeding, increased physical activity, etc.). When metabolic processes in a child are disrupted due to the development of pathological conditions, biochemical indicators are also characterized by a greater amplitude than in similar diseases in adults, which sometimes makes it difficult to correctly interpret laboratory tests in children.

Most biochemical parameters depend on the age of the child. A striking example of this is age-related variability in blood glucose levels. All of the above indicates the need to take into account the metabolic characteristics of the child’s body when assessing the metabolic status, diagnosing and treating diseases in the child.

Features of energy metabolism in children

Energy metabolism plays a leading role in the functioning of various organs and systems. All processes underlying the life of the body require energy expenditure. Each age period has its own characteristics of energy metabolism.

Prenatal period

During embryogenesis, tissue formation, growth and differentiation occur at high speed, which requires the formation of a significant amount of plastic material and the synthesis of functionally active proteins - enzymes.

The exceptional intensity of the growth processes determines the existence of intense energy metabolism even before the birth of the child. Placental blood circulation, functioning in the prenatal period, is characterized by a relatively low supply of oxygen to the fetus. As a result, anaerobic glycolysis occurs quite actively in the tissues of the developing embryo and fetus. This metabolic pathway, compared to aerobic glycolysis, provides less energy, glucose is consumed uneconomically, and a high level of energy production is ensured by increased consumption of glucose transplacentally from the mother’s blood.

Metabolic reactions of plastic and energy metabolism in the fetus are aimed at preparing for its existence outside the mother’s body. Childbirth is the greatest stress for a newborn child. The effectiveness of the fetus's adaptation to this stress is directly related to the accumulation in the body of substrates used for energy production. In the fetus, glycogen intensively accumulates in tissues (liver, muscle tissue, adrenal glands, etc.), mainly due to glucose coming from the mother’s blood. This early accumulation of glycogen in the liver allows premature babies to survive. Fats are also formed in the fetus's body, the source of which are chum bodies, which pass freely through the placental barrier. In the last 3 months of intrauterine life, 600-700 g of fat is deposited in the fetal body. Along with ordinary adipose tissue, brown adipose tissue is formed in the fetal body, which, having played its role immediately after birth, gradually disappears. The importance of this tissue lies in the processes of thermoregulation of newborns.

Extrauterine period

The entry of a child into the extrauterine environment is combined with a transition from placental to pulmonary gas exchange, a change in nutrition, and exposure of the newborn to a lower ambient temperature than in the mother’s body.

This temperature difference can be 15-18°. It significantly affects the metabolism of the newborn, and also causes a response from the child’s muscular system - the appearance of muscle tone, which ensures a high level of thermoregulation. Therefore, in the first hours of a newborn’s life, when the metabolic features of the intrauterine period are still preserved, but the environmental conditions are completely different, there is a significant tension in all body systems, which is reflected in the distinctive features of the child’s energy metabolism.

The general patterns of energy processes in children are the following:.

1) High energy demand of tissues. Per 1 kg of body weight, a child in the first and second half of life consumes 3 and 2.4 times more ATP, respectively, than an adult; A particularly high level of energy consumption is typical for the body of a newborn. The largest number of macroergs is used for actively occurring anabolic processes associated with intensive growth of the body and tissue differentiation. A significant part of the energy is spent on the functioning of the system for maintaining temperature homeostasis and the functioning of the motor system.

2) The peculiarities of heat exchange in children. The constancy of body temperature (temperature homeostasis) depends on the balance between heat loss and heat production. To maintain temperature homeostasis, the child’s body, even at rest, spends a lot of energy, and accordingly, a large amount of heat is released. The newborn has a limited ability to regulate heat output, which, when calculated per unit of body weight, can be 4 times higher than the heat output of an adult. The main reason for this is the larger body surface area relative to its mass than that of an adult, as well as a thin layer of subcutaneous fat that acts as thermal insulation. At the same time, a newborn has a significant ability to increase heat production, since the thermoregulation system in children depends on the ambient temperature.

When the child’s body cools, increased heat generation occurs as a result of contractile work of muscles (cold muscle tremors and cold muscle tone). This muscle activity is a powerful source of heat and is called shivering thermogenesis.

In addition, in a newborn and a young child (up to 1 year), the so-called non-shivering, or chemical, thermogenesis, associated with the direct oxidation of fat in brown adipose tissue, is of particular importance in the processes of heat production. In newborns, this tissue makes up 2% of body weight. Under the influence of cold, norepinephrine is released in brown adipose tissue, which is the main stimulator of lipolysis. Consequently, brown adipose tissue serves not only as a source of non-esterified fatty acids, but also as a site for their combustion with the formation of thermal energy, i.e. it is an important organ of heat production.

3) High sensitivity of energy metabolism to regulatory influences. The functionally immature thermoregulation system in young children is characterized by lability and is very sensitive to regulatory influences, for example, to the influence of substances that uncouple the chain of tissue respiration and oxidative phosphorylation (thyroxine, non-esterified fatty acids, microbial toxins). Under the influence of uncouplers, a significant part of the energy of the respiratory chain is not stored in the form of ATP, but is dissipated in the form of heat. In this regard, a discrepancy between heat transfer and heat production can easily occur, which manifests itself in an increase in body temperature and overheating of the body. Thermal lability in the body of children lasts up to 2 years.

4) High intensity of energy generation. To meet the child's significant energy needs, relatively large energy reserves of the body are required. The consequence of increased ATP consumption is the high intensity of bioenergetic processes, most pronounced in young children (especially newborns); subsequently it gradually decreases.

5) Switching energy production pathways from the embryonic type to the type characteristic of an adult. During the first year of a child’s life, qualitative changes occur in the nature of energy supply to tissues: the proportion of anaerobic glycolysis decreases and the intensity of oxidative phosphorylation processes increases. In newborns, the metabolic features of the intrauterine period are still preserved in the tissues, therefore the processes of anaerobic breakdown of carbohydrates predominate, which ensures high resistance of the body to hypoxia, but produces a small amount of macroergs. In the first three months after birth, the intensity of anaerobic glycolysis in children is highest and remains 30-35% higher during the first year of life than in adults.

By 3-4 months of age, a child experiences a restructuring of intracellular metabolism:

parallel to the decrease in anaerobic glycolysis, the intensity of redox processes increases, oxygen consumption increases, the predominance of aerobic glycolysis over anaerobic is stabilized, the energy needs of a growing organism are provided by a high level of oxidative phosphorylation. This general pattern of changes in metabolism towards the aerobic pathway of energy production allows tissues to use glucose more economically.

6) Changes in substrate support for energy processes. The use of substrates as energy sources changes during the first months of a child's life. Since in newborns the processes of anaerobic glycolysis prevail, which provide relatively little energy, and the level of energy consumption per unit of body weight is very high, to provide energy for vital processes in the first days after birth, the child spends reserves of energy substances accumulated “for future use” in the prenatal period.

The effectiveness of the child’s adaptation to extrauterine existence depends on the availability of these reserves.

In the first hours of life, a newborn uses glycogen as an endogenous source of energy. However, at birth the baby has insufficient glycogen reserves. At the moment of birth, the child’s blood sugar level corresponds to its mother’s concentration. Stress hormones released during childbirth quickly deplete glycogen stores in the liver. 2-3 hours after birth, the blood glucose level in newborns decreases to hypoglycemic values. Under such conditions, non-esterified fatty acids become the main source of energy. The cooling of the child’s body, which occurs after birth due to the transition from the mother’s body to a new environment, ensures the release of hormones

(thyroxine, in brown adipose tissue - norepinephrine, with the development of hypoglycemia - glucagon), which activate the breakdown of triglycerides with the formation of fatty acids. The concentration of non-esterified fatty acids in the blood increases, which are then used for energy purposes.

Since a child practically does not use proteins as an energy source in the first days after birth, and there are very few carbohydrates, the main endogenous source of energy for newborns is non-esterified fatty acids. The process of lipolysis occurs most intensively on days 3–4 after birth, which corresponds to the period of maximum weight loss in newborns. All tissues, except the brain and red blood cells, consume non-esterified fatty acids.

Simultaneously with non-esterified fatty acids, tissue use of ketone bodies, which also serve as an energy resource, increases. From the second week of life, the level of glucose in the blood of newborns gradually increases, and the content of non-esterified fatty acids decreases, but until 3 months of age it remains higher than in older children.

In such conditions, when, due to hypoglycemia, tissues cannot effectively use blood glucose, and intense lipolysis depletes the reserves of energy resources in the newborn’s body, the child’s body is at the limit of energy balance during the first week of life. Therefore, from a biochemical point of view, covering energy costs during this age period should be carried out by properly organizing the nutrition of children.

It is very important to feed the baby as early as possible to avoid increased catabolic processes in the body. An essential point is also the regularity of feeding, since skipping even one meal inevitably mobilizes fat reserves to eliminate a pronounced energy deficit. Starving a child at an early age is considered unacceptable, since it is accompanied by profound metabolic changes in the body, moreover, the more severe the younger the child.

Exogenous sources of energy in children are carbohydrates and fats (as in adults), and to a lesser extent proteins. In a young child, carbohydrates cover approximately 40% of the body's energy needs, fats cover about 50%, and in the first days of life, fats make up 80-90% of the energy value of the diet. As the child grows, the ratio changes in favor of carbohydrates.

Features of metabolism in children:

• · During child growth, anabolic processes exceed catabolic ones. The faster the child grows, the more pronounced this predominance is;
• · varies depending on the period of childhood relationship between
• · increase in body weight and differentiation of structures. Thus, in the breast period the increase in body weight is most pronounced. In pre-preschool, the process of formation of structures comes first. At school age - more complete differentiation of tissues;
• · Only in childhood does the necessary maturation of metabolic processes and the final formation of organs occur.

The energy that is generated in the human body as a result of metabolism during life is mainly used for basal metabolism, plastic metabolism, digestion and absorption of food products (specifically dynamic action of food), activity of the muscular system.

Basic exchange - this is the minimum amount of energy that is necessary to maintain the life of the organism in a state of complete rest; is installed in a child who is not sleeping and is in a state of complete muscular and emotional rest, at a comfortable temperature of 18-20°C, in the morning, on an empty stomach. Metabolism is measured by the number of kilocalories (kcal) that are released under specified conditions, per 1 kg of body weight or per 1 m2 of body surface in 1 hour or 1 day (according to the SI system - in kJ; 1 kcal = 4.184 kJ).

In newborns, there is an increase in basal metabolism, which gradually decreases by 1.5 years. Due to the high plastic metabolism at this age, the basal metabolism is lower than in an adult. In an adult it makes up 60% of the total energy, in a child of the first 3 months of life - 36%, i.e. 2 times less.

Plastic exchange - energy consumption for child growth. It is known that approximately 29.3 kJ (7 kcal) is consumed to accumulate 1 g of body weight. The most intensive growth is observed in the intrauterine period of development. The growth rate remains quite high in the first months of life, which is confirmed by a significant increase in body weight. Thus, in children of the first 3 months, the share of plastic metabolism is 46%, in 9 months - 13%, in 10-12 -6%. From the age of 4, especially in the prepubertal period, there is an increase in the intensity of growth and, accordingly, plastic metabolism.

On average, over 20 years of life, a person’s body weight increases approximately 20 times.

A certain amount of energy is spent on muscle system activity . Consumptionenergy muscle work increases with age and in adults it is 1/3 of daily energy expenditure. The share of energy consumption depends on the child’s upbringing, school load, etc.

The proportion of energy expended on the body's ability to accept, digest and assimilate food ( specific dynamic effect of food), varies depending on the nature of the diet. It is greater with foods rich in proteins, less when taking fats and carbohydrates. In children, especially young children, the specific dynamic effect of food is less pronounced (0.5% of daily energy expenditure) than in adults (10%).

FEATURES OF ENERGY EXCHANGE DURING DIFFERENT PERIODS OF CHILDHOOD

The peculiarities of energy metabolism in children are due to its intensive growth, high level of biosynthetic activity, as well as the functional immaturity of regulatory systems.

During the growth of a child’s body, metabolism and energy are characterized by significant quantitative and qualitative changes:

• · In utero maximum differentiation of tissues, formation of organs and systems occurs. During this period, body weight increases to the greatest extent, which is accompanied, accordingly, by the greatest energy consumption for plastic exchange(it takes 7 kcal to form 1 g of tissue);
• · perinatal period characterized by an active process of metabolic adaptation to new living conditions. A feature of the first days of a child’s life is a relatively low basal metabolic rate, which may be due to a decrease in thyroid function during this period. By the end of the neonatal period, the basal metabolism increases. Plastic exchange at this age continues to dominate in energy consumption over other types of energy expenditure. At this age, the exchange for digestion and absorption of food is turned on, and muscle metabolism also increases;
• · infancy characterized by the most intense metabolism and energy due to the growth of the child, the development of functional systems, the gradual abolition of breastfeeding, stabilization of the immune system, etc. Basic exchange continues to grow even in the second quarter of the first year of life exceeds plastic exchange by 1.5 times. At the end of the breast period BX reaches a maximum and exceeds the plastic value by more than 8 times.

Energy consumption for processes of digestion and absorption of food is determined by the needs of a child of the first year of life for proteins, fats and carbohydrates. To digest and assimilate proteins, more energy is needed than for fats and carbohydrates. Accordingly, the more protein a child’s food contains, the more energy is needed for its digestion and absorption.

• · preschool and preschool age: up to two years of life, stabilization of basal metabolic processes remains, from the 3rd year there is a gradual decrease in its intensity; preschool age is characterized by an increase in plastic metabolism;
• · V puberty Under the influence of sex hormones, significant changes in metabolic processes occur. Basic metabolic processes at 16-17 years of age correspond to the level of an adult.

In the body, along with the breakdown of substances, not only the release of energy occurs, but also a special type of its accumulation.