Metabolism and energy are the main properties of life. Metabolism and energy in the body Metabolism and energy conversion in the body

Metabolism and energy (metabolism) is a set of chemical reactions occurring in cells or in the whole organism and consisting in the synthesis of complex molecules and new protoplasm (anabolism) and the breakdown of molecules with the release of energy (catabolism). Energy is necessary for biosynthesis (formation of a new substance), osmotic work (absorption and secretion of various substances by cells), mechanical work (during movement) and other reactions.

Metabolism of substances and energy is the most important property of living things, manifested at different levels of organization of living things. Thanks to the metabolism and energy, growth and reproduction occur, and other important properties of cells and organisms are formed. A characteristic feature of the metabolic functions of animal and plant cells is that they are enzymatic and similar to each other, since the cells of all organisms possess all the molecules that play a central role in metabolism and ensure the transition of energy of one type into the energy of another type. In addition, the regulation of metabolic pathways is based on common mechanisms. Due to this, energy processes in all living beings are similar. Life exists and continues only thanks to energy

Anabolism and catabolism

The main metabolic processes are anabolism (assimilation) and catabolism (dissimilation).

Anabolism, or assimilation (from the Latin assimilatio - assimilation), is an endothermic process of assimilation of substances entering the cell to the substances of the cell itself. It is a “creative” metabolism.

The most important point in assimilation is the synthesis of proteins and nucleic acids. A special case of anabolism is photosynthesis, which is a biological process in which organic matter is synthesized from water, carbon dioxide and inorganic salts under the influence of radiant energy from the Sun. Photosynthesis in green plants is an autotrophic type of metabolism.

Catabolism, or dissimilation (from the Latin dissimilis - dissimilarity), is an exothermic process in which the breakdown of substances occurs with the release of energy. This breakdown occurs as a result of digestion and respiration. Digestion is the process of breaking down large molecules into smaller molecules, while respiration is the process of oxidative catabolism of simple sugars, glycerol, fatty acids and deaminated amino acids, resulting in the release of vital chemical energy. This energy is used to replenish adenosine triphosphate (ATP), which is the direct donor (source) of cellular energy, the universal energy “currency” in biological systems. Replenishment of ATP reserves is ensured by the reaction of phosphate (P) with adenosine diphosphate (ADP), namely:

ADP + P + ATP energy

When ATP is broken down into ADP and phosphate, the cell's energy is released and used for cellular work. ATP is a nucleotide consisting of adenine, ribose and triphosphate residues (triphosphate groups), while adenosine diphosphate (ADP) has only two phosphate groups. The energy richness of ATP is determined by the fact that its triphosphate component contains two phosphoanhydride bonds. The energy of ATP exceeds the energy of ADP by 7000 kcal/mol. This energy powers all biosynthetic reactions in the cell as a result of the hydrolysis of ATP to ADP and inorganic phosphate. So, the ATP-ADP cycle is the main mechanism of energy exchange in living systems.

Two laws of thermodynamics apply to living systems.

In accordance with the first law of thermodynamics (the law of conservation of energy), energy is neither created nor destroyed during chemical and physical processes, but simply passes from one form to another, suitable to one degree or another for performing work, i.e. the use of energy for performing any work or the transition of energy from one form to another is not accompanied by a change (decrease or increase) in the total amount of energy. With global categories in mind, we can say that despite any physical or chemical changes in the Universe, the amount of energy in it will remain unchanged.

In accordance with the second law of thermodynamics, physical and chemical processes proceed in the direction of the irreversible transition of useful energy into a chaotic, disordered form and the establishment of equilibrium between an ordered state and a chaotic, disordered one. As we approach the establishment of equilibrium between order and disorder and the process stops, the free energy decreases, i.e. that portion of total (useful) energy that is capable of producing work at constant temperature and constant pressure. When the amount of free energy decreases, that part of the total internal energy of the system increases, which is a measure of the degree of randomness and disorder (disorganization) and is called entropy. In other words, entropy is a measure of the irreversible transition of useful energy into a disordered form. Thus, the natural tendency of any system is to increase entropy and decrease free energy, which is the most useful thermodynamic function. Living organisms are highly ordered systems. They are characterized by containing a very large amount of information, but they are poor in entropy.

If the Universe is a reaction system, which is understood as a set of substances due to which physical and chemical processes occur, on the one hand, and the environment with which reaction systems exchange information, on the other hand, then in accordance with the second law of thermodynamics in the course of physical processes or chemical reactions, the entropy of the Universe increases. The metabolism of living organisms is not accompanied by an increase in internal disorder, i.e., age-related entropies are not characteristic of living organisms. In any conditions, all organisms, from bacteria to mammals, retain the orderly nature of their structure. However, what is characteristic of entropy itself is that it increases in the environment, and the continuous increase in entropy in the environment is ensured by living organisms existing in the environment. For example, to extract free energy, anaerobic organisms use glucose, which they obtain from the environment and oxidize with molecular oxygen, which also penetrates from the environment. In this case, the final products of oxidative metabolism (CO 2 and H 2 O) enter the environment, which is accompanied by an increase in the entropy of the environment, which is partly due to heat dissipation. The increase in entropy in this case increases, in addition, due to an increase in the number of molecules after oxidation (C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O), i.e., the formation of 12 molecules from 7 molecules. As can be seen, molecular disorder leads to entropy.

For living things, the primary source of energy is solar radiation, specifically visible light, which consists of electromagnetic waves occurring in discrete units called photons or quanta of light. In the living world, some living beings are able to capture light energy, while others receive energy as a result of the oxidation of food substances.

Visible light energy is captured by green plants during the process of photosynthesis, which occurs in the chloroplasts of their cells. Thanks to photosynthesis, living things create order out of disorder, and light energy is converted into chemical energy stored in carbohydrates, which are the products of photosynthesis. Thus, photosynthetic organisms extract free energy from sunlight. As a result, green plant cells have a high content of free energy.

The production of energy as a result of the oxidation of inorganic substances occurs during chemosynthesis.

Animal organisms obtain energy already stored in carbohydrates through food. Consequently, they contribute to an increase in the entropy of the environment. In the mitochondria of the cells of these organisms, the energy stored in carbohydrates is converted into a form of free energy suitable for the synthesis of molecules of other substances, as well as for ensuring the mechanical, electrical and osmotic work of cells. The release of energy stored in carbohydrates is carried out as a result of respiration - aerobic and anaerobic. During aerobic respiration, the breakdown of molecules containing stored energy occurs through glycolysis and the Krebs cycle. In anaerobic respiration, only glycolysis is active. Thus, the vital activity of the cells of animal organisms is provided mainly by energy, the source of which is the oxidation-reduction reactions of “fuel” (glucose and fatty acids), during which electrons are transferred from one compound (oxidation) to another (reduction). Phosphorylation is associated with redox reactions. These reactions occur during both photosynthesis and respiration.

The body is an open, self-regulating system; it maintains and replicates itself through the use of energy contained in food or generated by the Sun. Continuously absorbing energy and matter, life does not “strive” for a balance between order and disorder, between high molecular organization and disorganization. On the contrary, living beings are characterized by order both in their structure and functions, and in the transformation and use of energy. Thus, while maintaining internal order, but receiving free energy from sunlight or food, living organisms return an equivalent amount of energy to the environment, but in a less useful form, mainly in the form of heat, which, dissipating, goes into the Universe.

Metabolic and energy processes are subject to regulation, and there are many regulatory mechanisms. The main mechanism for regulating metabolism is the control of the amount of enzymes. Regulatory mechanisms also include control of the rate of substrate breakdown by enzymes, as well as control of the catalytic activity of enzymes. Metabolism is subject to what is known as reverse allosteric control, which means that in many biosynthetic pathways the first reaction can be inhibited by the end product. We can say that such inhibition occurs according to the feedback principle. In the regulation of metabolism and energy, it is also important that the metabolic pathways of synthesis and breakdown are almost always separated, and in eukaryotes this separation is enhanced by the compartmentalization of cells. For example, the site of fatty acid oxidation in cells is mitochondria, while their synthesis occurs in the cytosol. Many metabolic reactions are subject to some regulation by the so-called energy status of the cell, an indicator of which is the energy charge determined by the sum of the molar fractions of ATP and ADP. The energy charge in the cell is always constant. ATP synthesis is inhibited by high charge, while ATP utilization is stimulated by the same charge.

The main feature of a living organism is metabolism and energy. Plastic processes, processes of growth, and the formation of complex substances that make up cells and tissues continuously occur in the body. In parallel, the reverse process of destruction occurs. Every human activity involves the expenditure of energy. Even during sleep, many organs (heart, lungs, respiratory muscles) expend a significant amount of energy. The normal course of these processes requires the breakdown of complex organic substances, since they are the only sources of energy for animals and humans. These substances are proteins, fats and carbohydrates. Water, vitamins and mineral salts are also of great importance for normal metabolism. The processes of formation in the cells of the body of the substances it needs, the extraction and accumulation of energy (assimilation) and the processes of oxidation and decomposition of organic compounds, the transformation of energy and its consumption (dissimilation) for the needs of the body’s vital activity are closely intertwined, providing the necessary intensity of metabolic processes in general, balance receipt and consumption of substances and energy.

Metabolic processes proceed very intensively. Almost half of the body's tissues are renewed or replaced completely within three months. Over the course of 5 years of study, a student’s cornea is replaced 350 times, stomach tissue is renewed 500 times, red blood cells are produced up to 300 billion daily, and within 5-7 days half of all protein nitrogen in the liver is replaced.

Protein metabolism.Squirrels- a necessary building material for cell protoplasm. They perform special functions in the body. All enzymes, many hormones, visual purple of the retina, oxygen carriers, protective substances in the blood are protein bodies. Proteins are complex in structure and very specific. The proteins contained in food and the proteins in our body differ significantly in their qualities. If protein is extracted from food and injected directly into the blood, a person may die. Proteins are made up of protein elements - amino acids, which are formed during the digestion of animal and vegetable protein and enter the blood from the small intestine. The cells of a living organism contain more than 20 types of amino acids. Cells continuously undergo processes of synthesis of huge protein molecules consisting of chains of amino acids. The combination of these amino acids (all or part of them), connected in chains in different sequences, determines a countless number of different proteins.

Amino acids are divided into irreplaceable And replaceable. Essential are those that the body receives only from food. Nonessential ones can be synthesized in the body from other amino acids. The value of food proteins is determined by the amino acid content. That's why proteins coming from food are divided into two groups: full-fledged containing all essential amino acids, and inferior, which lack some essential amino acids. The main source of complete proteins is animal proteins. Plant proteins (with rare exceptions) are incomplete.

In tissues and cells, protein structures are continuously destroyed and synthesized. In a relatively healthy adult body, the amount of decomposed protein is equal to the amount of synthesized protein. Since protein balance in the body is of great practical importance, many methods have been developed to study it.

Protein balance is determined by the difference between the amount of protein received from food and the amount of protein that has undergone destruction during this time.

It is believed that the daily protein intake for an adult is 80-100 g. If more is consumed, then the excess protein goes to cover the body’s energy costs. At the same time, it can be transformed into carbohydrates and other compounds. During heavy physical activity, the body's need for protein can reach up to 150 g/day.

Carbohydrate metabolism.Carbohydrates- an important component of a living organism. However, there are fewer of them in the body than proteins and fats, they make up only about 2% of the dry matter of the body.

Carbohydrates are the main source of energy in the body. They are absorbed into the blood, mainly in the form of glucose. This substance is distributed throughout the tissues and cells of the body. In cells, glucose, with the participation of a number of factors, is oxidized to water and carbon dioxide (H2O and CO2.) At the same time, energy (4.1 kcal) is released, which is used by the body during synthesis reactions or during muscle work.

The importance of carbohydrates in muscle activity. Carbohydrate reserves are used especially intensively during physical work. However, they are never completely exhausted. When glycogen reserves in the liver decrease, its further breakdown stops, which leads to a decrease in the concentration of glucose in the blood. Muscular activity cannot continue under these conditions. A decrease in blood glucose is one of the factors contributing to the development of fatigue. Therefore, to successfully perform long and strenuous work, it is necessary to replenish the body’s carbohydrate reserves. This is achieved by increasing the content of carbohydrates in the diet and introducing them additionally before starting work or directly during work. Saturating the body with carbohydrates helps maintain a constant concentration of glucose in the blood and thereby increases human performance.

Regulation of carbohydrate metabolism. The deposition of carbohydrates, the use of carbohydrate reserves of the liver and other processes of carbohydrate metabolism are regulated by the central nervous system. The cerebral cortex is of great importance in the regulation of carbohydrate metabolism. One example of this is the conditioned reflex increase in blood glucose concentration in athletes in the pre-start state.

Efferent nerve pathways that provide regulation of carbohydrate metabolism belong to the autonomic nervous system. Sympathetic nerves enhance the breakdown processes and release of glycogen from the liver. Parasympathetic nerves, on the contrary, stimulate glycogen storage. Nerve impulses can act either directly on liver cells or indirectly through the endocrine glands. The adrenal medulla hormone adrenaline promotes the release of carbohydrates from the depot. The pancreatic hormone insulin ensures their deposition. In addition to these hormones, hormones from the adrenal cortex, thyroid gland and anterior pituitary gland participate in the regulation of carbohydrate metabolism.

Sugar contains 95% carbohydrates, honey - 76, chocolate - 49, potatoes - 18, milk -5, liver - 4, raisins - up to 65%.

Fat metabolism.Fats(lipids) are an important source of energy in the body, a necessary component of cells. Excess fats can be deposited in the body. They are deposited mainly in the subcutaneous fatty tissue, omentum, liver and other internal organs. The total amount of fat in a person can be 10-12% of body weight, and in case of obesity - 40-50%.

As an energy material, fat is used at rest and during long-term low-intensity physical work. At the beginning of intense muscle activity, carbohydrates are oxidized. But after some time, due to a decrease in glycogen reserves, fats and their breakdown products begin to oxidize. The process of replacing carbohydrates with fats can be so intense that 80% of all energy required under these conditions is released as a result of the breakdown of fat.

The metabolism of fat and lipids in the body is complex. The liver plays a major role in these processes, where fatty acids are synthesized from carbohydrates and proteins, and fat breakdown products are formed - ketone bodies, which are used as energy material. The formation of ketone bodies in the liver is especially intense when its glycogen reserves decrease.

Lipid metabolism is closely related to the metabolism of proteins and carbohydrates. During fasting, fat reserves serve as a source of carbohydrates.

Regulation of fat metabolism. Lipid metabolism in the body is regulated by the central nervous system. When some nuclei of the hypothalamus are damaged, fat metabolism is disrupted and the body becomes fat or depleted. Nervous regulation of fat metabolism is carried out through direct effects on tissue (trophic innervation) or through endocrine glands. Hormones of the pituitary gland, thyroid, pancreas and sex glands are involved in this process. With insufficient function of the pituitary gland, thyroid and gonads, obesity occurs. The pancreatic hormone insulin, on the contrary, enhances the formation of fat from carbohydrates, burning it.

100g of ghee or vegetable oil contains 95g of fat, sour cream - 24, milk - 4, fatty pork - 37, lamb - 29, liver, kidneys - 5, peas - 3, vegetables - 0.1-0.3g.

Exchange of water and minerals. The human body is 60% water. Adipose tissue contains 20% water (of its mass), bones - 25, liver - 70, skeletal muscles - 75, blood - 80, brain 85%.

For the normal functioning of an organism that lives in a changing environment, the constancy of the internal environment of the organism is very important. It is created by blood plasma, tissue fluid, lymph, the main part of which is water, proteins and mineral salts. Water and mineral salts do not serve as nutrients or sources of energy. But without water, metabolic processes cannot take place. Water is a good solvent.

A person can live no more than 7-10 days without water, while without food - 30-40 days. Water is removed along with urine through the kidneys (1700 ml), with sweat through the skin (500 ml) and with air exhaled through the lungs (300 ml).

The ratio of the total amount of fluid consumed to the total amount of fluid excreted is called water balance. If the amount of water consumed is less than the amount excreted, then various kinds of disorders of its functional state can be observed in the human body, since, being part of the tissues, water is one of the structural components of the body, is in the form of volitional solutions and determines the close connection of water metabolism with metabolism minerals.

Minerals are part of the skeleton, in the structures of proteins, hormones, and enzymes. The total amount of all minerals in the body is approximately 4-5% of body weight. Normal activity of the central nervous system, heart and other organs occurs under the condition of a strictly defined content of mineral ions, due to which the constancy of osmotic pressure and the reaction of blood and tissue fluid are maintained; they participate in the processes of secretion, absorption-excretion, etc.

A person receives the bulk of minerals from food and water. However, their content in food is not always sufficient. Most people have to add, for example, sodium chloride (NaCl - table salt) to their food, 10-12g per day. Chronic lack of minerals in food can lead to disruption of body functions.

Vitamins and their role in metabolism. Experiments show that even with a sufficient content of proteins, fats and carbohydrates in food, with optimal consumption of water and mineral salts, severe disorders and diseases can develop in the body, since the normal course of physiological processes also requires vitamins. The importance of vitamins is that, present in the body in minute quantities, they regulate metabolic reactions.

To date, more than 20 substances have been discovered that are classified as vitamins. They are usually designated by the letters of the Latin alphabet A, B, C, D, E, K, etc. Water-soluble vitamins include vitamins B, C, PP, etc. A number of vitamins are fat-soluble.

Vitamin A. With vitamin A deficiency, the body's growth processes are delayed and metabolism is disrupted. There is also a special eye disease called xerophthalmia (night blindness).

Vitamin D called antirachitic vitamin. Its deficiency leads to disorders of phosphorus and calcium metabolism. These minerals lose their ability to be deposited in the bones and are removed from the body in large quantities. At the same time, the bones soften and bend. The development of teeth is disrupted and the nervous system suffers. This entire complex of disorders characterizes the disease observed in children - rickets.

B vitamins. Lack or absence of B vitamins causes metabolic disorders and dysfunction of the central nervous system. At the same time, there is a decrease in the body's resistance to infectious diseases. Vitamins of group B are called vitamins of vigor, increased performance and strong nerves. The daily norm of vitamin B for an adult is 2-6 mg; with systematic sports activity, this norm should increase 3-5 times.

Vitamin C called antiscorbutic. If there is a lack of it in food (and most of it is found in fresh fruits and vegetables), a specific disease develops - scurvy, in which the gums bleed, and the teeth become loose and fall out. Physical weakness, fatigue, and nervousness develop. Shortness of breath, various hemorrhages appear, and sudden weight loss occurs. In severe cases, death may occur.

Vitamins affect metabolism, blood clotting, growth and development of the body, resistance to infectious diseases. Their role is especially important in the nutrition of the young body and those adults whose activities are associated with heavy physical activity at work and in sports.

Energy exchange. Metabolism and energy are interconnected processes. None of these processes exists separately. During oxidation, the energy of chemical bonds contained in nutrients is released and used by the body. Due to the transition of one type of energy to another, all vital functions of the body are supported. In this case, the total amount of energy does not change. The relationship between the amount of energy supplied by food and the amount of energy expenditure is called energy balance.

For normal functioning, the body must receive the optimal amount of complete proteins, fats, carbohydrates, mineral salts and vitamins, which are contained in various foods. The quality of food products is determined by their physiological value. The most valuable food products are milk, butter, cottage cheese, eggs, meat, fish, grains, fruits, vegetables, sugar.

People of different professions expend different amounts of energy in their activities. For example, a person engaged in intellectual work spends less than 3,000 large calories per day. A person engaged in heavy physical labor expends 2 times more energy per day.

Numerous studies have shown that a middle-aged man engaged in mental or physical labor for 8-10 hours needs to consume 118 g of protein, 56 g of fat, 500 g of carbohydrates per day. In terms of this, this amounts to about 3000 kcal.

Thus, in order to maintain energy balance, maintain normal body weight, ensure high performance and prevent various types of pathological phenomena in the body, it is necessary, with adequate nutrition, to increase energy consumption by increasing physical activity, which significantly stimulates metabolic processes.

The most important physiological “constant” of the body is the minimum amount of energy that a person expends in a state of complete rest. This constant is called basic exchange. The nervous system, heart, respiratory muscles, kidneys, liver and other organs continuously function and consume a certain amount of energy. The sum of these energy expenditures constitutes the basal metabolic rate.

Basal metabolism is an individual constant and depends on the gender, age, weight and height of a person. In a healthy person, it can remain at a constant level for a number of years. In childhood, the basal metabolic rate is much higher than in old age. The active state causes a noticeable intensification of metabolism. Metabolism under these conditions is called working metabolism. If the basic metabolism of an adult is 1700-1800 kcal, then the working metabolism is 2-3 times higher. Thus, the basal metabolic rate is the initial background level of energy consumption. A sharp change in basal metabolic rate can be an important diagnostic sign of fatigue, overexertion and under-recovery or disease.

Regulation of metabolism. The diencephalon section is of particular importance in the regulation of metabolism - hypothalamus. The destruction of this part of the central nervous system leads to a number of disorders of fat, carbohydrate and other types of metabolism. The hypothalamus regulates the activity of an important endocrine gland - the pituitary gland, which controls the work of all other endocrine glands, and they, in turn, by releasing hormones, carry out fine humoral regulation of metabolism at the cellular level. Various hormones (insulin, adrenaline, thyroxine) direct the activity of enzyme systems that regulate metabolic processes in the body. This coordinated relationship is achieved as a result of the interaction of the nervous and humoral (fluid) regulatory systems.

Conditioned reflex factors are essential for the regulation of basal metabolism. For example, in athletes, the basal metabolism turns out to be somewhat elevated on training days and, especially, competitions. In general, sports training, by economizing chemical processes in the body, leads to decrease in basal metabolism. This is more pronounced in individuals training for long-term, moderate-intensity work. However, in some cases, the basal metabolism is increased in athletes even on rest days. This is explained by a long-term (over several days) increase in the intensity of metabolic processes due to the intense work performed.

Many hormones influence basal metabolism.

Energy consumption during various forms of activity. A person’s daily energy expenditure includes the amount of basal metabolism and the energy necessary to perform professional work, sports and other forms of muscular activity. Mental work requires little energy expenditure. During physical work, energy consumption can reach large values. For example, when walking, energy is consumed by 80-100% more compared to rest, when running - by 400% or more.

Sports activity is accompanied by a significant increase in daily energy expenditure (up to 4500-5000 kcal). On days of training with increased loads and competitions in some sports (skiing, long-distance running, etc.), these values ​​can be even greater. All other things being equal, the energy consumption is greater, the relatively longer and more intense the work performed.

Muscle work is necessary for the normal functioning of the body. The amount of energy expended directly on physical work should be at least 1200-1300 kcal per day. In this regard, for people who do not engage in physical labor and spend less energy on muscular activity, physical exercise is especially necessary.

The level of energy expenditure is also influenced by emotions that arise during any activity. They can enhance or, conversely, reduce metabolism and energy in the body. Energy expenditure depends not only on the amount of work performed, but also on the environmental conditions in which the work is performed - temperature and humidity, barometric pressure, wind force.

After the end of muscular activity, energy expenditure remains elevated for some time compared to the resting level. This is due to chemical processes in the muscle associated with the oxidation of lactic acid and the elimination of oxygen debt.

Metabolism and energy involve a complex of complex biochemical reactions, which can be quite difficult for an ordinary person to understand. This article will help you understand what processes occur in the body with the necessary compounds that we consume with food and what affects our metabolism.

Energy exchange and metabolism proceed according to the general scheme:

• entry of substances into the body, its transformation and absorption;
• use in the body;
• removal or storage of surplus.

All metabolic processes are divided into 2 types:

1. Assimilation (plastic metabolism, anabolism) is the formation of organism-specific compounds from substances entering it.
2. Dissimilation is the process of decomposition of complex organic compounds into simpler ones, from which new, special substances will then be formed. Dissimilation reactions occur with the release of energy, therefore the combination of this type of process is also called energy exchange or catabolism.

These processes are opposite to each other, but are closely related. They flow continuously, ensuring normal life activities. The nervous system is responsible for regulating metabolism and energy. The main department of the central nervous system, which controls all types of metabolism, is the hypothalamus.

Main types

Depending on the forms of compounds that undergo transformation in the body, several types of metabolism are distinguished. Each of them has its own specifics.

Squirrels

Proteins or peptides are polymers formed by amino acids.

Perform many vital functions:

• structural (present in the structure of tissue cells that make up the human body);
• enzymatic (enzymes are proteins involved in almost all biochemical processes);
• motor (the interaction of actin and myosin peptides ensures all movements);
• energetic (decompose, releasing energy);
• protective (proteins - immunoglobulins are involved in the formation of immunity);
• participate in the regulation of water-salt balance;
• transport (provide delivery of gases, biologically active substances, medicines, etc.).

Once in the body with food, proteins break down into amino acids, from which new peptides characteristic of the body are then synthesized. With a low intake of protein from food, 10 of the 20 essential amino acids can be produced by the body, while the rest are essential.

Stages of protein metabolism:

• protein intake from food;
• breakdown of peptides to amino acids in the gastrointestinal tract;
• movement of the latter to the liver;
• distribution of amino acids in tissues;
• biosynthesis of specific peptides;
• removal of unused amino acids from the body in the form of salts.

Fats

The types of metabolism and energy in the human body include fat metabolism. Fats are compounds of glycerol and fatty acids. For a long time it was believed that their use is not necessary for the body to function properly. However, certain types of such substances contain significant anti-sclerotic components.

Fats, being an important source of energy, help preserve proteins in the body, which begin to be used to obtain it when there is a lack of carbohydrates and lipids. Fats are required for the absorption of vitamins A, E, D. Lipids are also contained in the cytoplasm and cell wall.

The biological value of fats is determined by the type of fatty acids with which they were formed. These acids can be of two types:

1. Saturated ones, which do not have double bonds in their structure, are considered the most harmful, since excessive consumption of foods high in this type of acid can cause atherosclerosis, obesity and other diseases. Present in butter, cream, milk, fatty meat.
2. Unsaturated - beneficial for the body. These include Omega-3, -6 and -9 acids. They help strengthen the immune system, restore hormonal levels, prevent cholesterol deposition, and improve the appearance of skin, nails and hair. Sources of such compounds are oils from various plants and fish oil.

Stages of lipid metabolism:

• intake of fats into the body;
• breakdown in the gastrointestinal tract to glycerol and fatty acids;
• formation of lipoproteins in the liver and small intestine;
• transport of lipoproteins into tissues;
• formation of specific cell lipids.

Excess fat is deposited under the skin or around internal organs.

Carbohydrates

Carbohydrates or sugars are the main source of energy in the body.

Carbohydrate metabolism processes:

• conversion of carbohydrates in the gastrointestinal tract into simple sugars, which are then absorbed;
• converting glucose into glycogen, storing it in the liver and muscles, or using it for energy production;
• conversion of glycogen into glucose by the liver if blood sugar levels drop;
• creation of glucose from non-carbohydrate components;
• conversion of glucose into fatty acids;
• oxygen decomposition of glucose to carbon dioxide and water.

In case of excessive consumption of foods rich in glucose, the carbohydrate is converted into lipids. They are deposited under the skin and can be used to further transform energy in cells.

The importance of water and mineral salts

Water-salt metabolism is a complex of processes of intake, application and removal of water and minerals. Most of the fluid enters the body from the outside. And it is also released in small volumes in the body during the decomposition of nutrients.

Functions of water in the body:

• structural (a necessary component of all tissues);
• dissolution and transport of substances;
• ensuring many biochemical reactions;
• an essential component of biological fluids;
• ensures the constancy of water-salt balance and participates in thermoregulation.

Fluid is removed from the body through the lungs, sweat glands, urinary system and intestines.

Mineral salts obtained from food can be divided into macro- and microelements. The first include minerals contained in significant quantities - magnesium, calcium, sodium, phosphorus and others. Microelements are needed by the body in very small quantities. These include iron, manganese, zinc, iodine and other elements.

A lack of minerals can negatively affect the functioning of various body systems. Thus, with a deficiency of magnesium and potassium, disruptions in the functioning of the central nervous system and muscles (including the myocardium) are observed. A lack of calcium and phosphorus can affect bone strength, and a lack of iodine can affect thyroid function. Violations of the water-salt balance can cause urolithiasis.

Vitamins

Vitamins are a large group of simple compounds necessary for the full functioning of all body systems.

Vitamins are divided into 2 groups:

• water-soluble (B vitamins, vitamin C and PP), which do not accumulate in the body;
• fat-soluble (A, D, E), having a similar accumulation property.

Certain compounds (vitamin B12, folic acid) are produced by intestinal microflora. Many vitamins are part of various enzymes, without which biochemical processes cannot be carried out.

Stages of vitamin metabolism:

• intake from food;
• moving to a place of accumulation or disposal;
• transformation into a coenzyme (a component of an enzyme of non-protein origin);
• a combination of coenzyme and apoenzyme (the protein part of the enzyme).

If there is a lack of any vitamin, hypovitaminosis develops; if there is an excess, hypervitaminosis develops.

Energy exchange

Energy metabolism (catabolism) is a complex of reactions of the breakdown of complex nutrients into simpler ones with the release of energy, without which growth and development, movement and other manifestations of life are impossible. The resulting energy is stored in the form of ATP (a universal energy source in living organisms), which is found in all cells.

The amount of energy released after eating a food is called its energy value. This indicator is measured in kilocalories (kcal).

Energy exchange takes place in several stages:

1. Preparatory. It involves the breakdown of complex nutrients in the gastrointestinal tract into simpler ones.
2. Anoxic fermentation is the transformation of glucose without the participation of oxygen. The process takes place in the cytoplasm of cells. The final products of this stage are 2 ATP molecules, water and pyruvic acid.
3. Oxygen or aerobic stage. It takes place in mitochondria (special cell organelles), while pyruvic acid breaks down with the participation of oxygen, forming 36 ATP molecules.

Thermoregulation

Thermoregulation is the ability of a living organism to maintain a constant body temperature, which is an important indicator of heat exchange. For this indicator to be stable, equality must be maintained between heat transfer and heat production.

Heat production is the release of heat in the body. Its source is the tissues in which reactions that release energy occur. Thus, the liver plays an important role in thermoregulation, because many biochemical processes are carried out in it.

Heat transfer or physical regulation can occur in three ways:

• heat conduction – transfer of heat to the environment and objects in contact with the skin;
• thermal radiation - the transfer of heat to the air and surrounding objects by emitting infrared (thermal) rays;
• Evaporation is the transfer of heat through the evaporation of moisture through sweat or during respiration.

What affects the metabolic process

The metabolism of each specific organism has its own characteristics. Metabolic rate is determined by several factors:

• gender (usually in men metabolic processes proceed somewhat faster than in women);
• genetic factor;
• proportion of muscle mass (people with developed muscles require more energy to work their muscles, so the processes occurring will proceed faster);
• age (metabolic rate decreases over the years);
• hormonal background.

Nutrition has a huge impact on the metabolic process. Both diet and food intake are important here. For proper functioning of the body, you need the optimal amount of consumed proteins, fats, carbohydrates, vitamins, minerals and fluids. It is important to remember that it is better to eat little by little, but often, since long breaks between meals contribute to a slowdown in metabolism, and therefore can lead to obesity.

METABOLISM AND ENERGY

General characteristics of metabolism and energy. Metabolism is the most general property characteristic of all living organisms. In the cytoplasm of the cells of organs and tissues, the process of synthesis of complex high-molecular compounds is constantly underway and, at the same time, their decay with the release of energy and the formation of simple low-molecular substances - carbon dioxide, water, ammonia, etc. The process of synthesis of organic substances is usually called assimilation or plastic exchange. The main chemical compounds of the cell (amino acids, nucleotides, etc.) are synthesized in the cell from glucose and ammonia as a result of several hundred sequential chemical reactions. Each step in this chain of reactions is carried out by a specific enzyme. During assimilation, cell organelles are renewed and energy reserves accumulate.

The process of decay of organic substances is called dissimilation. The disintegration of the structural elements of the cell is accompanied by the release of energy contained in chemical bonds, and the final products of decomposition, harmful to the body, are removed outside the cell and then from the body. This type of reaction occurs with the absorption of oxygen, so the breakdown of organic substances is associated with oxidation, and the energy released in this case goes to the synthesis of ATP, necessary for assimilation. All these processes occur with the participation of a large number of enzymes, ensuring a certain sequence of metabolic reactions in time, place and speed of their occurrence.

The reactions that occur during assimilation and dissimilation, although they represent directly opposite, mutually exclusive processes, in living organisms are closely interrelated and inseparable from each other, constituting two sides of a single metabolic process.

The essence of metabolism is that the body consumes various organic and inorganic compounds and chemical elements from the environment, uses them in its life activities and releases the final products of metabolism into the external environment in the form of simpler organic and inorganic compounds.

The importance of proteins for the body. Protein food products - meat, fish, eggs, cottage cheese and others, once in the digestive tract, are subjected to mechanical and chemical processing. In the stomach, protein is broken down into peptides, and in the duodenum into amino acids. In the small intestine, amino acids are absorbed into the blood and distributed to all organs and tissues. In a cell, proteins specific to a given tissue and a given organism are synthesized from amino acids. Some of the proteins that make up the cells of organs and tissues, as well as amino acids that enter the body but are not used in protein synthesis, undergo breakdown with the release of 17.6 kJ of energy per 1 g of substance with the formation of water, carbon dioxide, urea, ammonia and etc. Protein dissimilation products are excreted from the body in urine, sweat and partly with exhaled air. Proteins are not stored as reserves. In an adult, as many of them are synthesized as necessary to compensate for decayed proteins. When there is an excess of protein food, it is converted into fats and glycogen. The need for food proteins per day is 100-118 g. In childhood, the synthesis of proteins in the body exceeds their breakdown, which must be taken into account when preparing diets.

The importance of fats for the body. Fats are part of plant and animal foods. Part of the fat synthesized in the body is stored in reserve, the other part enters the cell, where, together with lipids, it serves as a plastic material from which the membranes of cells and organelles are built. Fats are the main source of energy. The breakdown of 1 g of fat is accompanied by the release of 38.9 kJ of energy, while carbon dioxide and water are released. Fats can be synthesized in the human body from carbohydrates and proteins. The daily requirement for an adult is 100 g.

The importance of carbohydrates for the body. Carbohydrates, which are part of plant products, are broken down into glucose in the human body. Glucose enters the blood and is distributed throughout the body. Its content in the blood is relatively constant and does not exceed 0.08-0.12%. If glucose enters the blood in large quantities, then the excess is converted in the liver into glycogen, which accumulates and then, if necessary, breaks down again into glucose. When 1 g of carbohydrates is broken down, 17.6 kJ of energy is released. Energy consumption increases in the body with increasing load during physical work. Part of the energy is used for mechanical work and serves as a source of heat, the other part goes to the synthesis of ATP molecules. When there is an excess of carbohydrates in the body, they turn into fats. The daily requirement of carbohydrates is 450-500 g.

The metabolism of proteins, fats and carbohydrates in the body is interconnected. Deviation from the norm of metabolism of one of these substances entails a violation of the metabolism of other substances. For example, in case of carbohydrate metabolism disorder, the products of their incomplete breakdown disrupt the metabolism of proteins and fats, the breakdown of which is also not complete, with the formation of toxic substances that poison the body.

The importance of water and mineral salts for the body. Along with the exchange of organic substances, water and salt exchange occur in the human body. These substances are not a source of energy or nutrients, but their importance for the body is great. Water is part of cells, intercellular and tissue fluid, plasma and lymph. Its total amount in the human body is 70%. In cells, water is chemically bonded with proteins, carbohydrates and other compounds. The absorption of nutrients in the intestine, their absorption by cells from tissue fluid and the removal of final metabolic products from cells can only be carried out in a dissolved state and with the participation of water. Water is a direct participant in all biochemical reactions of the body. The daily water requirement of an adult is 2-3 liters. Water enters the body when drinking and as part of food. In the small and large intestines, water is absorbed into the blood, then it enters the tissues. From tissue cells, along with decay products, it penetrates into the blood and lymph. Water is excreted from the body mainly through the kidneys, skin, lungs and feces. Water exchange is closely related to salt exchange.

Minerals enter the human body with food, are deposited in the form of salts and are part of various organic compounds. Thus, iron is included in the hemoglobin molecule and is involved in the transport of oxygen and carbon dioxide. Iodine is part of the thyroid hormone. Sulfur and zinc are found in pancreatic hormones. For normal hematopoiesis, iron, cobalt, and copper are needed. Calcium and phosphorus salts are part of bones. Potassium and sodium create a certain concentration of ions in the cell membrane and on either side of it. The total amount of minerals in the human body is about 4.5%.

A person needs a constant supply of sodium and chlorine. Sodium creates a certain concentration of ions in plasma and tissue fluid. Chlorine, being a component of hydrochloric acid, is part of gastric juice. All these elements enter the body with food, water and table salt. There is a lot of iron in apples, iodine in seaweed, calcium in milk, cheese, feta cheese, eggs, etc.

VITAMINS

This is an independent group of substances that are necessary for the functioning of the body. They have an effect on growth, metabolism and physical condition in general, and in fairly small quantities. Their chemical nature is diverse. Vitamins enter the body with food, are absorbed in human tissues and form part of enzymes that participate in metabolism. If vitamins are not supplied through food, physical health is impaired. This was proven in the last century by the Russian doctor N.I. Lunin, who discovered vitamins (vita means life). Further study revealed that they are involved in the synthesis and breakdown of amino acids, fats, nitrogenous bases of nucleic acids, hormones, as well as acetylcholine, which ensures the transmission of impulses in the nervous system. Vitamins are formed in plant organisms, but they are also found in products of animal origin. They are designated by capital letters of the Latin alphabet. Currently, more than twenty vitamins are known. They are divided into two groups - fat-soluble (A, D, E, K, etc.) and water-soluble (B, C, P, PP, etc.). Diseases that develop due to a lack of vitamins in the body are called avitaminosis or hypovitaminosis. A healthy adult requires only a few milligrams of various vitamins per day.

Vitamin C (ascorbic acid) is not synthesized in the human body. Its deficiency or absence in food is accompanied by scurvy. This is manifested primarily by bleeding gums. Then symptoms develop such as weakness, shortness of breath, bleeding and minor hemorrhages due to damage to the walls of blood vessels. Protein metabolism is disrupted, resistance to various diseases decreases. The human need for vitamin C is 63-105 mg per day. There is a lot of it in horseradish, pepper, rowan, currants, strawberries, cabbage, sorrel, rose hips, citrus fruits, etc. When food is heated, this vitamin is destroyed. People living in temperate, sharply continental and arctic climates experience hypovitaminosis in the spring due to a decrease in plant nutrition. Therefore, in winter and spring it is advisable to use additional ascorbic acid.

B vitamins (B 1, B 2, B 6, B 12, etc.) regulate many enzymatic metabolic reactions, especially the metabolism of proteins, amino acids, and nucleic acids. Lack or absence of vitamin B1 leads to beriberi disease. It is accompanied by a disorder of the nervous system, heart activity, and digestive system. This vitamin enters the body with wholemeal flour, peas, and brown rice. It is found in yeast (brewer's yeast), as well as in animal products - liver, kidneys, brain, heart muscle. A person needs 2-3 mg of this vitamin per day.

Lack or absence of vitamin B 12 is accompanied by the development of severe anemia. The vitamin is found in the liver and in the intestinal walls of animals, and is also synthesized by bacteria in the human intestines. If the secretory function of the stomach is impaired, the absorption of vitamins does not occur.

In the absence of group A vitamins in food, vision suffers due to the so-called night blindness or night blindness. In this case, the formation of visual pigments in the retina of the eyes is disrupted and the person sees poorly at dusk. In addition, changes occur in the skin and mucous membranes, desquamation of the epithelium increases, inflammation and softening of the mucous membrane and cornea of ​​the eyes occurs, and disruption of the epithelium of the genitourinary organs and digestive canal occurs.

Vitamin A is also called the growth vitamin; it is involved in redox metabolic reactions. Sources of the vitamin are animal products - liver, butter, fish oil. Plant products contain substances from which vitamin A is synthesized in the human body. These are carotenes from carrots, spinach, green onions, lettuce, red sweet peppers, etc. The need for vitamin A is 1-2 mg per day.

Vitamins of group D (D 2, D 3, etc.) play an important role in the metabolism of calcium and phosphorus. They are called antirachitic, since with a deficiency or absence of them, rickets develops. This disease manifests itself in early childhood and is accompanied by impaired bone formation. The bones become soft and curved, thickenings form on the ribs - rosaries. The formation of teeth is delayed and disrupted. The richest foods in vitamin D are fish liver, butter, egg yolk, caviar, and fish oil. An adult needs this vitamin with a normal diet; young children need 5-125 mcg. To prevent vitamin D deficiency, it is also necessary to have calcium and phosphorus salts and exposure to ultraviolet rays from the sun or quartz light sources, while provitamin D found in human skin is converted into vitamin D.

In addition to hypovitaminosis, hypervitaminosis is also currently observed due to excessive consumption of vitamins of synthetic origin, obtained at vitamin factories and freely offered in pharmacies. Hypervitaminosis negatively affects the health of adults, as metabolic processes are disrupted and is especially dangerous during pregnancy, when hypervitaminosis may result in the birth of an ugly child. Therefore, synthetic vitamins should be used on the recommendation of a doctor.

Methods for preserving vitamins in food products. To preserve vitamins in food, you must follow the rules for preparing and storing food. For example, in damaged vegetables and fruits, ascorbic acid is quickly destroyed due to the action of enzymes that break down their molecules. When preparing food, you must avoid overcooking and overcooking. The usefulness of fresh vegetables and fruits has always been known to man. Even in ancient times, people learned to prepare food for use - salting and fermenting, drying and smoking, drying, soaking and freezing. The word “canning” comes from the Latin word “conservare,” which means “to preserve.” There are many ways to preserve vitamins in food. For example, pickling, where acetic acid is used as a preservative. The basis of salting, soaking and fermentation is the process of lactic acid fermentation of vegetables and fruits from the influence of salt and sugar. Drying is the most ancient and very common method of canning (fruits, berries, vegetables, mushrooms). Freezing is the best, most perfect method of canning, since almost all the nutritional value of the products and their taste are preserved. This method has been known for a long time, but at home it has become widespread only now, when refrigerators with large freezers appeared.

Balanced diet. To ensure people's health, it is currently necessary to organize nutrition, which prevents increased fat deposition due to insufficient physical activity. The main principle of this diet is the use of a variety of foods, balanced in quantity and quality individually for each person. Nutrition should prevent the development of atherosclerosis, insufficient blood supply to the heart, myocardial infarction, hypertension, diseases of the digestive and excretory systems. In accordance with the objectives of rational nutrition, nutritional standards have been developed. The nutritional norm should be understood as the total amount of food and its components, corresponding to the biological nature of a person, which determines the favorable state of health of people of different ages, gender, lifestyle and work. The nutritional standards of the same person throughout his life change in accordance with his age, nature of work, state of health, etc. For an adult engaged primarily in mental work, it is recommended 167.4 kJ of energy per 1 kg of body weight, and for a person 221.7 kJ/kg, engaged in heavy physical labor. There are many groups of professions and for each, if necessary, a special nutritional standard is established. In accordance with energy consumption, the required amount of food is calculated based on the energy value of the resulting products. In the daily diet of adults, proteins, fats and carbohydrates are used in a ratio of 1:1:4. On average, an adult should consume 80-100 g of protein per day, the same amount of fat and 350-400 g of carbohydrates. Calculations are made based on the fact that 1 g of proteins and 1 g of carbohydrates release 16.7 kJ during combustion, and 1 g of fat releases 37.7 kJ.

For boys, 113 g of protein, 106 g of fat and 451 g of carbohydrates are recommended, and for girls, respectively, 96, 90, 383 g per day. For athletes during training and competitions, these standards are higher, but still lower for girls than for boys. An important feature of a balanced diet is the biological nutritional value, which also depends on the required amount of mineral salts and vitamins, and proteins and fats must be of both animal and plant origin.

Schoolchildren's diet. A regular and proper diet is important for all people, but especially in childhood. Food brings the greatest benefit to a person when taken at specific times. The most effective is four meals a day. At 7:30 a.m. - 8 a.m. - breakfast, which should account for 25% of the daily diet. At 11-12 o'clock second breakfast (10%). At 3-4 o'clock - lunch with the largest (45%) percentage of the daily diet. And at 8-9 o’clock - dinner (20% of the diet). If it is impossible to eat four meals a day, you should eat 30% of the daily diet at breakfast, up to 50% at lunch, and about 20% at dinner. It must be remembered that with irregular meals (one or two times a day), haste during meals and frequent consumption of difficult-to-digest foods, inflammation of the gastric mucosa (gastritis) develops.

Metabolism and energy is a set of chemical and physical transformations that occur in the cells and tissues of a living organism and ensure its viability. The essence of metabolism or metabolism is the sequential consumption by the body of various substances from the external environment, the assimilation, use, accumulation and loss of substances and energy throughout life, allowing the body to self-preserve, grow, develop, adapt to the environment and self-reproduce.

Metabolic processes occur in the form of successive phases: 1) extraction of energy from organic substances that enter the body with food; 2) transformation of the breakdown products of nutrients into “building blocks” for the synthesis of substances specific to the body; 3) synthesis of proteins, nucleic acids, fats, carbohydrates and other cell elements; 4) synthesis and destruction of those biologically active molecules that are necessary for the implementation of specific functions of the body.

The purpose of metabolism and energy is: firstly, to provide the plastic needs of the body, that is, to deliver to the body the chemicals necessary for the construction of its structural elements and the restoration of substances that disintegrate in the body and are lost from the body; secondly, in providing all vital functions of the body with energy.

Highlight BX(occurring at complete rest) and intermediate metabolism (the set of chemical transformations from the moment digested food substances enter the blood until the release of metabolic products from the body).

Metabolism is divided into two interconnected and simultaneously occurring processes in the cell - assimilation (anabolism) and dissimilation (catabolism). During anabolism, complex substances are biosynthesized from simpler precursor molecules. At the same time, each cell synthesizes its characteristic squirrels, fats, carbohydrates and other connections. During catabolism, large organic molecules are broken down into simple compounds with the simultaneous release of energy, which is stored mainly in the form of ATP. Catabolism refers to energy metabolism, which ensures the delivery to cells of the energy necessary for life. During life, different quantitative relationships between the processes of assimilation and dissimilation are observed: in a growing organism, assimilation predominates; from approximately the age of 22-25 to 60 years, a relative balance of anabolism and catabolism is established; after 60 years, the processes of dissimilation slightly exceed the processes of assimilation, which is accompanied by changes in the functional capabilities of various body systems.

The main stages of metabolism and their significance. The main substances necessary for the functioning of the body are squirrels, fats, carbohydrates, minerals, vitamins And water. The metabolic processes of these substances have their own characteristic features. But along with this, there are general patterns that allow us to distinguish three stages of metabolism: 1) processing of food products in the digestive organs, 2) interstitial metabolism, 3) formation of final metabolic products.

First stage- this is the sequential breakdown of the chemical components of food in the gastrointestinal tract into low-molecular structures and the absorption of the resulting simple chemical products into the blood or lymph.

The breakdown of proteins, fats and carbohydrates occurs under the influence of specific enzymes. Proteins are broken down by peptides into amino acids, fats by lipases into glycerol and fatty acids, complex carbohydrates by amylases into monosaccharides. The energy value of the first stage of metabolism is insignificant and consists mainly in the conversion of nutrients into their simplest forms, which can subsequently serve as an energy source. These forms are amino acids (about 20), three hexoses (glucose, fructose and galactose), pentose, some rarer sugars, glycerol and fatty acids. They are easily absorbed into the blood and lymph, carried by the bloodstream to the liver and peripheral tissues, where they undergo further transformations.

Second phase metabolism combines the transformation of amino acids, monosaccharides, glycerol and fatty acids. The process of interstitial metabolism leads to the formation of a few key compounds that determine the cross-talk between individual metabolic pathways, as well as between the processes of synthesis and breakdown; figuratively they are called the metabolic cauldron, or the general metabolic cauldron (Fig. 21). Such a compound, for example, is pyruvic acid, pyruvate, which plays the role of a link between carbohydrates, fats and most amino acids. Pyruvic acid is a common breakdown product of carbohydrates, fats and the nitrogen-free residue of some amino acids. Along with this, pyruvic acid can serve as a product for the synthesis of carbohydrates and fats, and also participate in the transamination of amino acids.

The main key product is acetyl coenzyme A (“active acetate”), which is formed as a result of multi-stage oxidative decarboxylation of pyruvic acid and the subsequent addition of coenzyme A. Acetyl coenzyme A is a nucleotide containing an energy-rich sulfide bond. 0H is easily subject to further oxidation, and also serves as a unifying link for the metabolism of fatty acids and some amino acids.

As a result, the metabolism of fats, proteins and carbohydrates is reduced to a common path - the tricarboxylic acid cycle (Krebs cycle), the oxidative breakdown of the final products of metabolism of carbohydrates, fats and amino acids. Thus, the processes of metabolism of carbohydrates, fats and proteins are interconnected at the stage of key metabolic products and have a common final path (Fig. 21).

Squirrels		Carbohydrates		Fats
âá		âá		â
Amino acids		Monosaccharides		Glycerol		Fatty acid
â		âá		âá
	Pyruvic acid
		â
		Acetyl coenzyme A
		â
		Tricarboxylic acid cycle	2H	Respiratory chain
		à
		ß
		2H
		à
		â â	2H
		H 2 O CO 2

Rice. 21. Diagram of the relationship between the metabolism of carbohydrates, proteins, and fats (according to: Drzhevetskaya, 1994)

The processes of interstitial metabolism lead to the synthesis of species-specific proteins, fats and carbohydrates and their complexes - nucleoproteins, phospholipids, etc., that is, to the formation of the constituent parts of the body. Along with this, interstitial exchange processes serve as the main source of energy. The main part of the energy (2/3) is released as a result of oxidation in the Krebs cycle. During the intermediate transformations of carbohydrates, fats and proteins, the released energy is converted into the energy of special chemical compounds, the so-called macroergs, that is, compounds in which a lot of energy accumulates.

In the human body, the function of macroergs is performed by various phosphorus compounds, mainly adenosine triphosphoric acid (ATP). It is in ATP that 60-70% of all energy released during the interstitial metabolism of nutrients is accumulated. And only 30-40% of the energy released during the oxidation of proteins, fats and carbohydrates is converted into thermal energy and released from the body into the external environment in the process of heat transfer.

Third stage exchange consists in the formation and release of final products of exchange. Nitrogen-containing products are excreted in urine (mainly), feces and in small quantities through the skin. Carbon is excreted mainly in the form of CO 2 through the lungs and partly in urine and feces. Hydrogen is released primarily in the form of water through the lungs and skin, as well as in urine and feces. Mineral compounds are excreted in the same way.

Protein metabolism. The importance of proteins. Proteins or proteins are high-molecular organic compounds built from amino acid residues. Proteins occupy a leading place among organic elements, accounting for more than 50% of the dry mass of the cell. They perform the following functions:

1) plastic - the main building material of cellular structures (part of the cytoplasm, hemoglobin, and many hormones);

2) enzymatic - protein enzymes catalyze metabolic processes (respiration, digestion, excretion);

3) energy - provide the body with energy generated from the breakdown of proteins;

4) protective - blood plasma proteins provide immunity;

5) homeostatic - maintain the constancy of the body’s water-salt environment;

6) motor - the interaction of the contractile proteins actin and myosin during muscle contraction.

Proteins are the material carriers of life and form the basis of all cellular structures. Protein biosynthesis determines the growth, development and self-renewal of all structural elements in the body. The important role of proteins determines the need for their frequent renewal. The rate of protein turnover is different for different tissues. Proteins in the liver, intestinal mucosa, as well as other organs and blood plasma are renewed at the highest speed. For example, in the human liver, about 25 g of new protein is formed daily, about 20 g are replaced in the cytoplasm per day, and about 8 g are replaced in hemoglobin. Under normal conditions, up to 400 g of new protein is produced daily in the body of an adult and the same amount breaks down. Half of the protein composition of the liver is replaced by new protein within just 5-7 days. The proteins that make up the cells of the brain, heart, and gonads are renewed more slowly, and even more slowly the proteins of muscles, skin, and especially supporting tissues (tendons, bones, cartilage).

Complete and incomplete proteins. The body's protein metabolism is closely related to protein nutrition. The amino acid composition of food is of great importance for protein synthesis. All amino acids used in protein synthesis are divided into two groups: 1) non-essential, the lack of which in food can be compensated for by other amino acids, and 2) essential or vital, not formed in the body, the lack of which causes disruption of protein synthesis.

It has been established that of the 20 amino acids that make up proteins, 12 are synthesized (essential amino acids), and 8 are not synthesized (essential amino acids). Without essential amino acids, protein synthesis is dramatically disrupted: growth stops and body weight falls. Essential amino acids include valine, leucine, isoleucine, threonine, methionine, phenylalline, tryptophan, lysine. For example, the absence of the amino acid lysine in food leads to stunted growth of a child and depletion of his muscular system. Valine deficiency causes balance disorders in children.

Animal foods contain more essential amino acids than plant foods. Proteins that contain the entire required set of amino acids are called biologically complete. The highest biological value of proteins is milk, eggs, fish, and meat. Inferior proteins are proteins from corn, wheat, barley. It should be noted that two defective proteins with different amino acid compositions can jointly meet the body's needs. In this regard, the child’s food should not only contain a sufficient amount of protein, but also include proteins with high biological value, that is, of animal origin.

Stages of protein metabolism. Protein metabolism is the process of assimilation (synthesis, breakdown and excretion) of nitrogen-containing compounds (mainly proteins and amino acids) by the cells and tissues of the body.

Protein synthesis occurs from amino acids and low molecular weight polypeptides, which are formed during the breakdown of proteins in the digestive system into amino acids and are absorbed into the blood.

Enzymatic breakdown of proteins is carried out by proteinases of digestive juices - gastric, pancreatic, intestinal.

Intermediate protein metabolism. Amino acids and peptides absorbed in the intestine are transported by the blood to the liver and peripheral tissues. Here, some of them are used for the synthesis of body proteins, and some go to the formation of a number of amino acid derivatives (purine and phosphatidic bases). Finally, some amino acids undergo deamination, that is, the removal of the amino group from amino acids and their conversion into nitrogen-free products. Amino groups split off during deamination are excreted from the body in the urine in the form of ammonia and urea.

Thus, interstitial protein metabolism consists of several phases: 1) protein biosynthesis; 2) breakdown of tissue proteins, 3) conversion of amino acids. In the process of interstitial exchange of amino acids, physiologically active substances appear: hormones, nucleotides, coenzymes (Fig. 22).

As a result of interstitial protein metabolism, end products are formed (ammonia, uric acid, creatine). Urea is the main end product formed during protein metabolism. It is synthesized in the liver from ammonia released during the deamination of amino acids.

Nitrogen balance - the ratio of the amount of nitrogen entering the body with food and released from it. Since proteins contain nitrogen, the nitrogen balance can be used to judge the ratio of the amount of protein received and destroyed in the body:

Knowing how much nitrogen is absorbed, it is easy to calculate the amount of protein introduced into the body. On average, protein contains 16% nitrogen, that is, 1 g of nitrogen in 6.25 g of protein, therefore, by multiplying the amount of absorbed nitrogen by 6.25, you can determine the amount of protein introduced into the body. The amount of daily protein breakdown is determined in the same way. There is a certain relationship between the amount of nitrogen introduced with food proteins and the amount of nitrogen excreted from the body. This condition is called nitrogen balance. Consequently, in a state of nitrogen equilibrium, the breakdown of protein structures in the body is quantitatively balanced by food proteins. Nitrogen balance characterizes the normal course of protein metabolism processes in the body under conditions of sufficient protein nutrition.

Protein food		Tissue proteins
â decay		â decay
Peptides		Peptides
â		â
	Amino acids
neoplasm â		â interconversion
Substances of non-protein nature		Amino acids
Amino acids	NH 3	Urea
â
Tissue proteins	synthesis	decay
	Biologically active substances: hormones, nucleotides, coenzymes	decay	Metabolites of the tricarboxylic acid cycle
		â
		CO 2 H 2 O

Rice. 22. Ways of using amino acids in intracellular metabolism
(By: Andreeva et al., 1998)

In cases where nitrogen intake exceeds its release - positive nitrogen balance. In this case, protein synthesis prevails over its breakdown. A stable positive nitrogen balance is always observed with an increase in body weight and is noted during the period of body growth, during pregnancy due to fetal growth, during the period of recovery after serious illnesses, as well as during intense sports training, accompanied by an increase in muscle mass. In these cases, nitrogen retention occurs in the body (nitrogen retention).

Proteins are not deposited in the body, that is, they are not stored. Therefore, when a significant amount of protein is consumed with food, only part of it is spent for plastic purposes, while the majority is spent for energy purposes. In this regard, the child needs to be given the optimal amount of protein, with a set of all amino acids.

When the amount of nitrogen excreted from the body exceeds the amount taken in, it is determined as negative nitrogen balance. Negative nitrogen balance occurs when there is a complete absence or insufficient amount of protein in food, as well as when consuming food containing incomplete proteins. In all these cases, protein starvation occurs. With protein starvation, the intensity of protein synthesis and breakdown decreases.

A decrease in the activity of protein synthesis, especially functionally essential proteins, leads to disruption of the functioning of organs and systems. A growing organism especially suffers: growth is inhibited, the formation of the skeleton is disrupted, which is due to a lack of plastic material necessary for the construction of cellular structures.

Age-related features of protein metabolism. In a child’s body, processes of growth and formation of new cells and tissues occur intensively. Therefore, the need for proteins in a child is much higher than in an adult. The more intense the growth processes, the greater the need for protein.

The Institute of Nutrition of the Russian Academy of Medical Sciences has developed norms for the daily protein requirement per 1 kg of body weight for children: up to 1 year - 5-5.5 g, from 1 to 3 years - 4-4.5 g, from 4 to 7 years - 3.5-4 g, from 8 to 12 years - 3 g and over 12 years - 2-2.5 g. At these values, nitrogen is retained in the body as much as possible. Not only the quantity, but also the quality of the protein introduced is important. The completeness of proteins is determined by the presence in them of amino acids necessary for the construction of proteins in the child’s body.

With age, the need for individual essential and non-essential amino acids changes. Children of the 1st year of life need not only a much larger amount of nucleic acids, but also a qualitatively different composition of food amino acids. At the same age, the greatest retention of protein in the body is observed, as body weight rapidly increases. The greatest positive nitrogen balance is observed in the first 3 months of life.

Subsequently, the balance value, remaining positive all the time, falls and by the end of the year there are no significant changes in the nitrogen balance. So, for example, according to A.F. Tolkachevskaya (1960), nitrogen retention in children of the 1st year of life in g/kg averages: 3 months - 0.28, 3-6 months - 0.20, 6- 9 months - 0.21, 9-12 months - 0.23 (quoted from: Markosyan, 1969). The degree to which the body uses nitrogen varies individually. Both consumption and retention of dietary nitrogen depend not only on the age-related needs of the body, but also on the amount of protein introduced with food. A child, unlike an adult, has the ability to temporarily accumulate protein. The more nitrogen is introduced with food, the greater its retention in the body (Table 34).

Table 34. Nitrogen retention in preschool children with different protein content in the diet (according to: Makkhamov, 1959)

The best nitrogen retention in children from 1.6 to 3 years of age is observed with a daily dose of protein equal to 4 g per 1 kg of weight. It has been established that for children 7-8 years old, a daily dose of protein equal to 2.2-2.5 g per 1 kg of weight only maintains nitrogen balance. At a lower dose the balance is negative, and at a dose of 2.8-3 g per 1 kg of weight it becomes positive.

With age, the amount of under-oxidized products in the urine increases, the ratios between individual fractions of nitrogen and sulfur in urine change, and changes occur in the secretion of lactic acid and creatine.

The lowest content of total nitrogen in urine occurs in the first 3 months of life, and in subsequent months and up to the 1st year there is an increase in nitrogen content in urine. The daily amount of nitrogen excreted in the urine, especially during the first 4 years of life, increases rapidly. At 4-6 years of age, total urine nitrogen ranges from 98-162 mg/h. The amount of nitrogen per 1 kg of weight reaches its maximum value by 6 years, and then begins to gradually decrease.

Per 1 kg of weight, the amount of urea, gradually increasing in the 1st year of life, doubles in the 2nd year, then gradually increases again until 5-6 years, after which it begins to fall. So, for example, if a newborn excretes 0.17 g of urea per 1 kg of weight in the urine, then a 6-year-old - 0.81, and a 13-year-old - 0.64.

Thus, the period of the most intensive growth corresponds to the least release of urea. Regarding the content in the urine of children uric acid, then its excretion per 1 kg of weight during the first year of life significantly exceeds that of an adult. The uric acid content is especially high in the first 3 months, then decreases somewhat, but by the end of the year it still exceeds the adult norm by 2-4 times. The daily amount of uric acid increases fairly evenly with age and is 260 mg in the 2nd year of life, 560 mg at 10 years, 600 mg at 13 years, and 800 mg in an adult. At the same time, the relative excretion of uric acid decreases with age.

Another feature of children’s nitrogen metabolism is the constant presence of creatine in their urine. Normally, creatine is not excreted in the urine of adults, but in children, starting from the moment of birth, the excretion of creatine in the urine continues until puberty. With age, the excretion of creatine in the urine decreases significantly, the concentration of creatinine increases, and by the age of 15-16 it approaches the level of an adult.

At the age of 5-6 years, there are no gender differences in the release of both creatine and creatinine; they appear only at 10-13 years, and girls have more creatine release than boys.

In terms of creatinine excretion, sex differences arise from about 9 years of age and become more noticeable at 14-16 years of age. In boys, the daily amount of creatinine excreted in urine is much higher than in girls. These gender differences are apparently explained by the greater development of the muscular system in boys compared to girls of the same age.