Importance of carbohydrate and protein metabolism. Protein metabolism. Fat metabolism. The exchange of carbohydrates. The liver, its role in metabolism

METABOLISM OF PROTEINS, FATS AND CARBOHYDRATES IN THE BODY.

1. general characteristics metabolism in the body.

2. Protein metabolism.

3. Fat metabolism.

4. Metabolism of carbohydrates.

PURPOSE: to represent general scheme metabolism in the body, the metabolism of proteins, fats, carbohydrates and manifestations of the pathology of these types of metabolism.

1. Once in the body, nutrient molecules participate in a variety of various reactions. These reactions, as well as other chemical manifestations of vital activity, are called metabolism, or metabolism. Nutrients are used as raw materials for the synthesis of new cells or are oxidized, delivering energy to the body. Part of this energy is necessary for the continuous construction of new tissue components, the other is consumed in the process of cell functioning: during muscle contraction, transmission nerve impulses, secretion of cellular products. The rest of the energy is released as heat.

Metabolic processes are divided into anabolic and catabolic. Anabolism (assimilation) - chemical processes, at which simple substances combine with each other to form more complex ones, which leads to the accumulation of energy, the construction of a new protoplasm and growth. Catabolism (dissimilation) - the splitting of complex substances, leading to the release of energy, while the destruction of protoplasm and the expenditure of its substances.

The essence of metabolism: 1) the intake of various nutrients into the body from the external environment; 2) their assimilation and use in the process of life as sources of energy and material for building tissues; 3) the release of the resulting metabolic products into the external environment.

Specific functions of metabolism: 1) extracting energy from environment in the form of chemical energy of organic substances; 2) the transformation of exogenous substances into building blocks, i.e. precursors of the macromolecular components of the cell; 3) the assembly of proteins, nucleic acids and other cellular components from these blocks; 4) the synthesis and destruction of biomolecules necessary to perform various specific functions of this cell.

2. Protein metabolism - a set of plastic and energy processes transformation of proteins in the body, including the exchange of amino acids and their decay products. Proteins - the basis of all cellular structures, are the material carriers of life. Protein biosynthesis determines the growth, development and self-renewal of all structural elements in the body and thus their functional reliability. The daily requirement for proteins (protein optimum) for an adult is 100-120 g (with an energy expenditure of 3000 kcal / day). All amino acids (20) must be at the disposal of the body in a certain ratio and quantity, otherwise the protein cannot be synthesized. Many protein amino acids (valine, leucine, isoleucine, lysine, methionine, threonine, phenylalanine, tryptophan) cannot be synthesized in the body and must be supplied with food (essential amino acids). Other amino acids can be synthesized in the body and are called non-essential (histidine, glycocol, glycine, alanine, glutamic acid, proline, hydroxyproline, series, tyrosine, cysteine, arginine,). Proteins are divided into biologically complete (with a complete set of all essential amino acids) and defective (in the absence of one or more essential amino acids).

The main stages of protein metabolism: 1) enzymatic breakdown of food proteins to amino acids and absorption of the latter; 2) transformation of amino acids; 3) protein biosynthesis; 4) protein breakdown; 5) the formation of end products of the breakdown of amino acids.

sucked in blood capillaries villi of the mucous membrane of the small intestine, amino acids according to portal vein arrive at a time where they are immediately used, or held up as a small reserve. Some of the amino acids remain in the blood and enter other cells of the body, where they are incorporated into new proteins. Body proteins are continuously broken down and re-synthesized (renewal period total protein in the body - 80 days). If the food contains more amino acids than is necessary for the synthesis of cellular proteins, liver enzymes split off NH2 amino groups from them, i.e. produce deamination. Other enzymes, connecting the amino groups that have been cleaved off with CO2, form urea from them, which is transferred with the blood to the kidneys and excreted in the urine. Proteins are not deposited in the depot, so the proteins that the body consumes after the depletion of carbohydrates and fats are not reserve, but enzymes and structural proteins of cells.

Protein metabolism disorders in the body can be quantitative and qualitative. O quantitative changes protein metabolism is judged by the nitrogen balance, i.e. according to the ratio of the amount of nitrogen entering the body with food and excreted from it. Normally in an adult adequate nutrition the amount of nitrogen introduced into the body is equal to the amount excreted from the body (nitrogen balance). When the intake of nitrogen exceeds its excretion, they speak of a positive nitrogen balance, and nitrogen is retained in the body. It is observed during the period of body growth, during pregnancy, during recovery .. When the amount of nitrogen excreted from the body exceeds the amount received, they speak of a negative nitrogen balance. It is noted during significant reduction protein content in food (protein starvation).

3. Fat metabolism - a set of processes for the transformation of lipids (fats) in the body. Fats are energy and plastic material, are part of the membrane and cytoplasm of cells. Part of the fat accumulates in the form of reserves (10-30% of body weight). The bulk of fats are neutral lipids (triglycerides of oleic, palmitic, stearic and other higher fatty acids). The daily requirement for fats for an adult is 70-100 g. The biological value of fats is determined by the fact that some unsaturated fatty acids (linoleic, linolenic, arachidonic), necessary for life, are indispensable ( daily requirement 10-12 g). and cannot be formed in the human body from other fatty acids, so they must be supplied with food (vegetable and animal fats).

The main stages of fat metabolism: 1) enzymatic breakdown of food fats into gastrointestinal tract to glycerol and fatty acids and the absorption of the latter into small intestine; 2) the formation of lipoproteins in the intestinal mucosa and in the liver and their transport by blood; 3) the hydrolysis of these compounds on the surface of cell membranes by the enzyme lipoprotein lipase, the absorption of fatty acids and glycerol into cells, where they are used to synthesize their own lipids of cells of organs and tissues. After synthesis, lipids can undergo oxidation, releasing energy, and eventually turn into carbon dioxide and water (100 g of fat gives 118 g of water when oxidized). Fat can be transformed into glycogen, and then undergo oxidative processes of the type carbohydrate metabolism. With an excess of fat is deposited in the form of reserves in subcutaneous tissue, greater omentum, around some internal organs.

With food rich in fat, comes a certain amount of lipoids (fat-like substances) - phosphatides and sterols. Phosphatides are necessary for the body to synthesize cell membranes; they are part of the nuclear substance, the cytoplasm of cells. rich in phosphatides nervous tissue. The main representative of sterols is cholesterol. It is also part of cell membranes, is a precursor of the hormones of the adrenal cortex, gonads, vitamin D, bile acids. Cholesterol increases the resistance of erythrocytes to hemolysis, serves as an insulator for nerve cells providing the conduction of nerve impulses. Normal content total cholesterol in blood plasma 3.11-6.47 mmol / l.

4. Carbohydrate metabolism - a set of processes for the transformation of carbohydrates in the body. Carbohydrates are energy sources for direct use (glucose) or form an energy depot (glycogen), are components of complex compounds (nucleoproteins, glycoproteins) used to build cellular structures. The daily requirement is 400-500 g.

The main stages of carbohydrate metabolism: 1) the breakdown of food carbohydrates in the gastrointestinal tract and the absorption of monosaccharides in the small intestine; 2) the deposition of glucose in the form of glycogen in the liver and muscles or its direct use for energy purposes; 3) the breakdown of glycogen in the liver and the entry of glucose into the blood as it decreases (glycogen mobilization); 4) the synthesis of glucose from intermediate products (pyruvic and lactic acids) and non-carbohydrate precursors; 5) the conversion of glucose into fatty acids; 6) oxidation of glucose with the formation of carbon dioxide and water.

Carbohydrates are absorbed in the alimentary canal in the form of glucose, fructose and galactose. They travel via the portal vein to the liver, where fructose and galactose are converted to glucose, which is stored as glycogen. The process of glycogen synthesis in the liver from glucose is called glycogenesis (the liver contains 150-200 g of carbohydrates in the form of glycogen). Part of the glucose enters the general circulation and is distributed throughout the body, being used as the main energy material and as a component of complex compounds (glycoproteins, nucleoproteins).

Glucose is constant integral part(biological constant) of blood. The content of glucose in the blood is normally 4.44-6.67 mmol / l, with an increase in its content (hyperglycemia) to 8.34-10 mmol / l, it is excreted in the urine in the form of traces. With a decrease in blood glucose (hypoglycemia) to 3.89 mmol / l, a feeling of hunger appears, to 3.22 mmol / l - convulsions, delirium and loss of consciousness (coma) occur. When glucose is oxidized in cells for energy, it eventually turns into carbon dioxide and water. The breakdown of glycogen in the liver to glucose is glycogenolysis. Biosynthesis of carbohydrates from their breakdown products or breakdown products of fats and proteins - gluconeogenesis. The breakdown of carbohydrates in the absence of oxygen with the accumulation of energy in ATP and the formation of milk and pyruvic acid- glycolysis.

When glucose intake exceeds demand, the liver converts glucose into fat, which is stored in fat depots and can be used as an energy source in the future. Violation normal exchange carbohydrates is manifested by an increase in blood glucose. Persistent hyperglycemia and glucosuria associated with deep violation carbohydrate metabolism is observed in diabetes mellitus. The basis of the disease is insufficiency of the endocrine function of the pancreas. Due to the lack or absence of insulin in the body, the ability of tissues to use glucose is impaired, and it is excreted in the urine.

Metabolism begins with the intake nutrients into the gastrointestinal tract and air into the lungs.

The first stage of metabolism is the enzymatic processes of splitting proteins, fats and carbohydrates into water-soluble amino acids, mono- and disaccharides, glycerol, fatty acids and other compounds occurring in various departments gastrointestinal tract, as well as the absorption of these substances into the blood and lymph.

The second stage of the exchange is the transport of nutrients and oxygen by the blood to the tissues and those complex chemical transformations of substances that occur in cells. They simultaneously carry out the breakdown of nutrients to the final products of metabolism, the synthesis of enzymes, hormones, and components of the cytoplasm. The breakdown of substances is accompanied by the release of energy, which is used for the processes of synthesis and ensuring the work of each organ and the organism as a whole.

The third stage is the removal of end products of decay from cells, their transport and excretion by the kidneys, lungs, sweat glands and intestines.

The transformation of proteins, fats, carbohydrates, minerals and water occurs in close interaction with each other. The metabolism of each of them has its own characteristics, and their physiological significance is different, so the exchange of each of these substances is usually considered separately.

Protein metabolism

Proteins are used in the body primarily as plastic materials. The need for protein is determined by the minimum amount that will balance its loss by the body. Proteins are in a state of continuous exchange and renewal. In the body of a healthy adult, the amount of protein decomposed per day is equal to the amount of newly synthesized. Ten of the 20 amino acids (valine, leucine, isoleucine, lysine, methionine, tryptophan, threonine, phenylalanine, arginine and histidine) cannot be synthesized in the body if they are insufficiently supplied with food and are called essential. The other ten amino acids (non-essential) can be synthesized in the body.

Proteins specific for a given species, organism and for each organ are synthesized from the amino acids obtained during digestion. Some of the amino acids are used as an energy material, i.e. undergo splitting. First, they are deaminated - they lose the Nh3 group, resulting in the formation of ammonia and keto acids. Ammonia is toxic substance and is detoxified in the liver by conversion to urea. Keto acids after a series of transformations decompose into CO2 and H2O.

The rate of decay and renewal of body proteins is different - from several minutes to 180 days (80 days on average). The amount of protein that has undergone decay per day is judged by the amount of nitrogen excreted from the human body. 100 g of protein contains 16 g of nitrogen. Thus, the excretion of 1 g of nitrogen by the body corresponds to the breakdown of 6.25 g of protein. About 3.7 g of nitrogen is released from the body of an adult per day, i.e. the mass of the destroyed protein is 3.7 x 6.25 = 23 g, or 0.028-0.075 g of nitrogen per 1 kg of body weight per day (Rubner wear coefficient).

If the amount of nitrogen entering the body with food is equal to the amount of nitrogen excreted from the body, then the body is in a state of nitrogen balance.

If more nitrogen enters the body than is excreted, then this indicates a positive nitrogen balance (nitrogen retention). It occurs when the mass muscle tissue(intense physical activity), during the period of body growth, pregnancy, during recovery after serious illness. The state in which the amount of nitrogen excreted from the body exceeds its intake into the body is called a negative nitrogen balance. It occurs when eating defective proteins, when any of the essential amino acids do not enter the body, with protein or complete starvation.

It is necessary to consume at least 0.75 g of protein per 1 kg of body weight per day, which for an adult healthy person weighing 70 kg is at least 52.5 g of complete protein. For reliable stability of the nitrogen balance, it is recommended to take 85-90 g of protein per day with food. In children, pregnant and lactating women, these rates should be higher. Physiological significance in this case means that proteins mainly perform a plastic function, and carbohydrates - energy.

Metabolism of fats (lipids)

Lipids are esters of glycerol and higher fatty acids. Fatty acids are either saturated or unsaturated (containing one or more double bonds). Lipids play an energy and plastic role in the body. Due to the oxidation of fats, about 50% of the energy needs of an adult organism are provided. Fats serve as a reserve of nutrition for the body, their reserves in humans average 10-20% of body weight. Of these, about half are in the subcutaneous adipose tissue, a significant amount is deposited in the greater omentum, perirenal tissue and between the muscles.

In a state of hunger, when the body is exposed to cold, during physical or psycho-emotional load there is an intensive breakdown of stored fats. Under conditions of rest after eating, resynthesis and deposition of lipids in the depot occurs. The main energy role is played by neutral fats - triglycerides, and the plastic is carried out by phospholipids, cholesterol and fatty acids, which perform the functions of structural components of cell membranes, are part of lipoproteins, are precursors steroid hormones, bile acids and prostaglandins.

Lipid molecules absorbed from the intestine are packed in epitheliocytes into transport particles (chylomicrons), which enter the bloodstream through the lymphatic vessels. Under the action of lipoprotein lipase of the capillary endothelium main component chylomicrons - neutral triglycerides - are broken down to glycerol and free fatty acids. Part of the fatty acids can bind to albumin, while glycerol and free fatty acids enter fat cells and are converted to triglycerides. The remnants of blood chylomicrons are captured by hepatocytes, undergo endocytosis and are destroyed in lysosomes.

Lipoproteins are formed in the liver for the transport of lipid molecules synthesized in it. These are very low lipoproteins and lipoproteins low density that transport triglycerides and cholesterol from the liver to other tissues. Low-density lipoproteins are captured from the blood by tissue cells with the help of lipoprotein receptors, are endocytosed, release cholesterol for the needs of cells and are destroyed in lysosomes. When excess accumulation low-density lipoproteins in the blood, they are captured by macrophages and other leukocytes. These cells, accumulating metabolically low-active cholesterol esters, become one of the components of atherosclerotic vascular plaques.

Lipoproteins high density transport excess cholesterol and its esters from the tissues to the liver, where they are converted into bile acids, which are excreted from the body. In addition, high-density lipoproteins are used for the synthesis of steroid hormones in the adrenal glands.

Both simple and complex lipid molecules can be synthesized in the body, with the exception of unsaturated linoleic, linolenic and arachidonic fatty acids, which must be supplied with food. These essential acids are part of the molecules of phospholipids. Prostaglandins, prostacyclins, thromboxanes, leukotrienes are formed from arachidonic acid. The absence or insufficient intake of essential fatty acids in the body leads to growth retardation, impaired kidney function, skin diseases, and infertility. The biological youth of dietary lipids is determined by the presence of essential fatty acids in them and their digestibility. Butter and pork fat are digested by 93 - 98%, beef - by 80 - 94%, sunflower oil - by 86 - 90%, margarine - by 94-98%.

Carbohydrate metabolism

Carbohydrates are the main source of energy, and also perform plastic functions in the body; during the oxidation of glucose, intermediate products are formed - pentoses, which are part of nucleotides and nucleic acids. Glucose is necessary for the synthesis of certain amino acids, the synthesis and oxidation of lipids, polysaccharides. The human body receives carbohydrates mainly in the form of the plant polysaccharide starch and in a small amount in the form of an animal glycogen polysaccharide. In the gastrointestinal tract, they are broken down to the level of monosaccharides (glucose, fructose, lactose, galactose).

Monosaccharides, the main of which is glucose, are absorbed into the blood and through the portal vein enter the liver. Here fructose and galactose are converted into glucose. The intracellular concentration of glucose in hepatocytes is close to its concentration in the blood. When excess glucose enters the liver, it is phosphorylated and converted into a reserve form of its storage - glycogen. The amount of glycogen in an adult can be 150-200 g. In the case of restriction of food intake, with a decrease in blood glucose levels, glycogen is broken down and glucose enters the blood.

During the first 12 hours or more after a meal, the maintenance of blood glucose concentration is provided by the breakdown of glycogen in the liver. After the depletion of glycogen stores, the synthesis of enzymes increases, providing the reactions of gluconeogenesis - the synthesis of glucose from lactate or amino acids. On average, a person consumes 400-500 g of carbohydrates per day, of which usually 350-400 g is starch, and 50-100 r are mono- and disaccharides. Excess carbohydrates are stored as fat.

Water and mineral metabolism

The water content in the body of an adult is on average 73.2 ± 3% of body weight. Water balance in the body is maintained due to the equality of the volume of water loss and its intake into the body. The daily need for water ranges from 21 to 43 ml/kg (on average 2400 ml) and is satisfied by drinking water (~1200 ml), food (~900 ml) and water formed in the body during metabolic processes ( endogenous water (~300 ml).The same amount of water is excreted in urine (~1400 ml), feces (~100 ml), through evaporation from the surface of the skin and respiratory tract(~900 ml).

The body's need for water depends on the nature of the diet. When eating predominantly carbohydrate and fatty foods and with a small intake of NaCl, the need for water is less. Food, rich in proteins, as well as increased reception salts cause a greater need for water, which is necessary for excretion osmotically active substances(urea and mineral ions). Insufficient intake of water or its excessive loss leads to dehydration, which is accompanied by thickening of the blood, deterioration of its rheological properties and hemodynamic disturbances.

The lack of water in the body in the amount of 20% of body weight leads to lethal outcome. Excessive intake of water into the body or a decrease in its volumes excreted by the body leads to water intoxication. As a result hypersensitivity nerve cells and nerve centers to a decrease in osmolarity, water intoxication may be accompanied by muscle cramps.

The exchange of water and mineral ions in the body are closely interrelated, due to the need to maintain osmotic pressure at a relatively constant level in the extracellular environment and in cells. Implementation of a number physiological processes(excitation, synoptic transmission, muscle contraction) is impossible without maintaining a certain concentration of Na +, K +, Ca2 + and other mineral ions in the cell and in the extracellular environment. All of them must be ingested with food.

1. General characteristics of the metabolism in the body.

2. Protein metabolism.

3. Fat metabolism.

4. Metabolism of carbohydrates.

PURPOSE: To present the general scheme of metabolism in the body, the metabolism of proteins, fats, carbohydrates and the manifestations of the pathology of these types of metabolism.

1. Once in the body, food molecules are involved in many different reactions. These reactions, as well as other chemical manifestations of vital activity, are called metabolism, or metabolism. Nutrients are used as raw materials for the synthesis of new cells or are oxidized, delivering energy to the body. Part of this energy is necessary for the continuous construction of new tissue components, the other is consumed in the process of cell functioning: during muscle contraction, transmission of nerve impulses, secretion of cellular products . The rest of the energy is released as heat.

Metabolic processes are divided into anabolic and catabolic. Anabolism (assimilation) - chemical processes in which simple substances combine with each other to form more complex ones, which leads to the accumulation of energy, the construction of new protoplasm and growth. Catabolism (dissimilation) - the splitting of complex substances, leading to the release of energy, while the destruction of protoplasm and the expenditure of its substances.

Specific functions of metabolism: 1) extraction of energy from the environment in the form of chemical energy of organic substances; 2) transformation of exogenous substances into building blocks, i.e. precursors of the macromolecular components of the cell; 3) assembly of proteins, nucleic acids and other cellular components from these blocks; 4) synthesis and destruction of biomolecules necessary to perform various specific functions of a given cell.

2. Protein metabolism - a set of plastic and energy processes of protein transformation in the body, including the exchange of amino acids and their decay products. Proteins - the basis of all cellular structures, are the material carriers of life. Protein biosynthesis determines the growth, development and self-renewal of all structural elements in the body and thus their functional reliability. The daily requirement for proteins (protein optimum) for an adult is 100-120 g (with an energy expenditure of 3000 kcal / day). All amino acids (20) must be at the disposal of the body in a certain ratio and quantity, otherwise the protein cannot be synthesized. Many protein amino acids (valine, leucine, isoleucine, lysine, methionine, threonine, phenylalanine, tryptophan) cannot be synthesized in the body and must be supplied with food (essential amino acids). Other amino acids can be synthesized in the body and are called non-essential (histidine, glycocol, glycine, alanine, glutamic acid, proline, hydroxyproline, series, tyrosine, cysteine, arginine,). Proteins are divided into biologically complete (with a complete set of all essential amino acids) and incomplete (in the absence of one or more essential amino acids).

Having been absorbed into the blood capillaries of the villi of the mucous membrane of the small intestine, the amino acids enter the portal vein into the stream, where they are immediately used, or retained as a small reserve. Some of the amino acids remain in the blood and enter other cells of the body, where they are incorporated into new proteins. Body proteins are continuously broken down and synthesized again (the period of renewal of the total protein in the body is 80 days). If the food contains more amino acids than is necessary for the synthesis of cellular proteins, liver enzymes split off NH2 amino groups from them, i.e. produce deamination. Other enzymes, connecting the amino groups that have been cleaved off with CO2, form urea from them, which is transferred with the blood to the kidneys and excreted in the urine. Proteins are not deposited in the depot, so the proteins that the body consumes after the depletion of carbohydrates and fats are not reserve, but enzymes and structural proteins of cells.

Protein metabolism disorders in the body can be quantitative and qualitative. Quantitative changes in protein metabolism are judged by the nitrogen balance, i.e. according to the ratio of the amount of nitrogen entering the body with food and excreted from it. Normally, in an adult with adequate nutrition, the amount of nitrogen introduced into the body is equal to the amount excreted from the body (nitrogen balance). When the intake of nitrogen exceeds its excretion, they speak of a positive nitrogen balance, and nitrogen is retained in the body. It is observed during the period of body growth, during pregnancy, during recovery. When the amount of nitrogen excreted from the body exceeds the amount received, they speak of a negative nitrogen balance. It is noted with a significant decrease in the protein content in food (protein starvation).

3. Fat metabolism - a set of processes for the transformation of lipids (fats) in the body. Fats are an energy and plastic material, they are part of the shell and cytoplasm of cells. Part of the fat accumulates in the form of reserves (10-30% of body weight). The bulk of fats are neutral lipids (triglycerides of oleic, palmitic, stearic and other higher fatty acids). The daily requirement for fats for an adult is 70-100 g. The biological value of fats is determined by the fact that some unsaturated fatty acids (linoleic, linolenic, arachidonic), necessary for life, are indispensable (daily requirement 10-12 g) and cannot be formed in the human body from other fatty acids, so they must be supplied with food (vegetable and animal fats).

The main stages of fat metabolism: 1) enzymatic breakdown of food fats in the gastrointestinal tract to glycerol and fatty acids and absorption of the latter in the small intestine; 2) the formation of lipoproteins in the intestinal mucosa and in the liver and their transport by blood; 3) the hydrolysis of these compounds on the surface of cell membranes by the enzyme lipoprotein lipase, the absorption of fatty acids and glycerol into cells, where they are used to synthesize their own lipids of cells of organs and tissues. After synthesis, lipids can undergo oxidation, releasing energy, and eventually turn into carbon dioxide and water (100 g of fat gives 118 g of water when oxidized). Fat can be converted into glycogen, and then undergo oxidative processes similar to carbohydrate metabolism. With an excess, fat is deposited in the form of reserves in the subcutaneous tissue, the greater omentum, around some internal organs.

With food rich in fats, a certain amount of lipoids (fat-like substances) - phosphatides and sterols - comes. Phosphatides are necessary for the body to synthesize cell membranes; they are part of the nuclear substance, the cytoplasm of cells. Phosphatides are especially rich in nervous tissue. The main representative of sterols is cholesterol. It is also part of cell membranes, is a precursor of the hormones of the adrenal cortex, gonads, vitamin D, bile acids. Cholesterol increases the resistance of red blood cells to hemolysis, serves as an insulator for nerve cells, ensuring the conduction of nerve impulses. The normal content of total cholesterol in blood plasma is 3.11-6.47 mmol / l.

Glucose is a constant component (biological constant) of blood. The content of glucose in the blood is normally 4.44-6.67 mmol / l, with an increase in its content (hyperglycemia) to 8.34-10 mmol / l, it is excreted in the urine in the form of traces. With a decrease in blood glucose (hypoglycemia) to 3.89 mmol / l, a feeling of hunger appears, to 3.22 mmol / l - convulsions, delirium and loss of consciousness (coma) occur. When glucose is oxidized in cells for energy, it eventually turns into carbon dioxide and water. The breakdown of glycogen in the liver to glucose is glycogenolysis. Biosynthesis of carbohydrates from their breakdown products or breakdown products of fats and proteins - gluconeogenesis. The breakdown of carbohydrates in the absence of oxygen with the accumulation of energy in ATP and the formation of lactic and pyruvic acids - glycolysis.

When glucose intake exceeds demand, the liver converts glucose into fat, which is stored in fat depots and can be used as an energy source in the future. Violation of the normal metabolism of carbohydrates is manifested by an increase in the content of glucose in the blood. Constant hyperglycemia and glucosuria associated with a profound violation of carbohydrate metabolism is observed in diabetes mellitus. The basis of the disease is insufficiency of the endocrine function of the pancreas. Due to the lack or absence of insulin in the body, the ability of tissues to use glucose is impaired, and it is excreted in the urine.

GOAL: Represent the general scheme of metabolism in the body, the metabolism of proteins, fats, carbohydrates and the manifestations of the pathology of these types of metabolism.

Glucose is a constant component (biological constant) of blood. The content of glucose in human blood is normally 4.44-6.67 mmol / l, with an increase in its content (hyperglycemia) to 8.34-10 mmol / l, it is excreted in the urine in the form of traces. With a decrease in blood glucose (hypoglycemia) to 3.89 mmol / l, a feeling of hunger appears, to 3.22 mmol / l - convulsions, delirium and loss of consciousness (coma) occur.

When glucose is oxidized in cells for energy, it eventually turns into carbon dioxide and water. The breakdown of glycogen in the liver to glucose is glycogenolysis. Biosynthesis of carbohydrates from their breakdown products or breakdown products of fats and proteins - gluconeogenesis. The breakdown of carbohydrates in the absence of oxygen with the accumulation of energy in ATP and the formation of lactic and pyruvic acids - glycolysis.

When glucose intake exceeds demand, the liver converts glucose into fat, which is stored in fat depots and can be used as an energy source in the future.

Violation of the normal metabolism of carbohydrates is manifested by an increase in the content of glucose in the blood. Constant hyperglycemia and glucosuria associated with a profound violation of carbohydrate metabolism is observed in diabetes mellitus. The basis of the disease is insufficiency of the endocrine function of the pancreas. Due to the lack or absence of insulin in the body, the ability of tissues to use glucose is impaired, and it is excreted in the urine.

During a lifetime, a person eats about 10 tons of carbohydrates. Carbohydrates enter the body mainly in the form of starch. Splitting into digestive tract to glucose, carbohydrates are absorbed into the blood and absorbed by cells. Plant foods are especially rich in carbohydrates: bread, cereals, vegetables, fruits. Animal products (with the exception of milk) are low in carbohydrates.

Carbohydrates are the main source of energy, especially with increased muscle work. More than half of the energy the body of adults receives from carbohydrates. The end products of carbohydrate metabolism are carbon dioxide and water.

In the blood, the amount of glucose is maintained at a relatively constant level (about 0.11%). A decrease in glucose content causes a decrease in body temperature, a disorder of activity nervous system, fatigue. The liver plays an important role in maintaining a constant blood sugar level. An increase in the amount of glucose causes its deposition in the liver in the form of reserve animal starch - glycogen. Glycogen is mobilized by the liver when blood sugar drops. Glycogen is formed not only in the liver, but also in the muscles, where it can accumulate up to 1-2%. Glycogen reserves in the liver reach 150 g. During starvation and muscular work, these reserves are reduced.

Usually when used a large number carbohydrates in the urine appears sugar, and thereby levels out the sugar content in the blood.

However, there may be a persistent increase in blood sugar in the blood, which does not even out. It occurs when there is a malfunction of the glands. internal secretion(for example, the pancreas), which leads to the development of the disease diabetes . With this disease, the ability to bind sugar to glycogen is lost and an increased excretion of sugar in the urine begins.

The value of glucose for the body is not limited to its role as an energy source. Glucose is part of the cytoplasm and, therefore, is necessary for the formation of new cells, especially during the growth period.

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

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

The need for glucose in different organs is not the same. The brain retains up to 12% of glucose brought in, intestines - 9%, muscles - 7%, kidneys - 5%. The spleen and lungs consume almost no glucose at all.

Fat metabolism

The total amount of fat in the human body varies widely and averages 10-12% of body weight, and in cases of obesity can reach 50% of body weight. The amount of stored fat depends on the nature of the diet, the amount of food consumed, gender, age, etc.

Dietary fat in the digestive tract is broken down into glycerol and fatty acids, which are absorbed mainly into the lymph and only partially into the blood.

Fatty acids are saponified during absorption, i.e., together with alkalis and bile acids, they form soluble complexes that pass through the intestinal mucosa. Already in cages intestinal epithelium the body's own fat is synthesized.

Through the lymphatic circulatory system fats are mainly found in adipose tissue, which is important for the body fat depot. There is a lot of fat in the subcutaneous tissue, around some internal organs (for example, the kidneys), as well as in the liver and muscles.

Fat is used by the body as a rich source of energy. With the breakdown of 1 g of fat in the body, more than two times more energy is released than with the breakdown of the same amount of proteins or carbohydrates. Fats are also part of the cells (cytoplasm, nucleus, cell membranes), where their number is stable and constant. Accumulations of fat can perform other functions. For example, subcutaneous fat prevents increased heat transfer, perirenal fat protects the kidney from bruises, etc.

The lack of fat in food disrupts the activity of the central nervous system and reproductive organs, reduces endurance to various diseases.

Fats are synthesized in the body not only from glycerol and fatty acids, but also from the metabolic products of proteins and carbohydrates.

This is the basis for the practice of fattening farm animals for lard.

The species specificity of fats is less pronounced than the species specificity of proteins. This is evidenced by experiments conducted on dogs. The dogs were forced long time starve, and when they lost almost all their reserve fat, one of them was given with food linseed oil and the other is mutton fat. After some time, it was found that the first dog's own fat became liquid and resembled linseed oil in some properties, and the fat of the second dog was similar in consistency to lamb fat.

Some unsaturated fatty acids necessary for the body(linoleic, linolenic and arachidonic), must enter the body in finished form, since they are not able to be synthesized by them. Unsaturated fatty acids are found in vegetable oils(most of them are in linseed and hemp oil). Lots of linoleic acid and sunflower oil. This explains the high nutritional value margarine, which contains a significant amount of vegetable fats.

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

For 1 kg of adult weight per day, 1.25 g of fat should be supplied with food (60-80 g per day).

In the cells of the body, fats are decomposed into glycerol and fatty acids by the action of cellular enzymes (lipases). The transformation of glycerol (with the participation of ATP) ends with the formation of carbon dioxide and water. Fatty acids under the action of many enzymes undergo complex transformations with the formation as an intermediate product acetic acid, which is then converted to acetoacetic acid. The end products of fatty acid metabolism are carbon dioxide and water. The transformations of unsaturated fatty acids in the body have not yet been studied enough.