Violation of carbohydrate metabolism. Carbohydrate metabolism in the human body: we improve without pills and regulate the process of losing weight Disorders of carbohydrate metabolism

Carbohydrates are organic, water-soluble substances. They are made up of carbon, hydrogen, and oxygen, with the formula (CH 2 O) n , where ‘n’ can range from 3 to 7. Carbohydrates are found mainly in plant foods (with the exception of lactose).

Based on the chemical structure, they are divided into three groups:

monosaccharides
oligosaccharides
polysaccharides

Types of carbohydrates

Monosaccharides

Monosaccharides are the "basic units" of carbohydrates. The number of carbon atoms distinguishes these basic units from each other. The suffix "ose" is used to identify these molecules in the category of sugars:

triose is a monosaccharide with 3 carbon atoms
tetrose is a monosaccharide with 4 carbon atoms
pentose is a monosaccharide with 5 carbon atoms
hexose is a monosaccharide with 6 carbon atoms
heptose - monosaccharide with 7 carbon atoms

The hexose group includes glucose, galactose and fructose.

, also known as blood sugar, is the sugar into which all other carbohydrates in the body are converted. Glucose can be obtained through digestion or formed as a result of gluconeogenesis.
Galactose does not occur in free form, but more often in combination with glucose in milk sugar (lactose).
Fructose, also known as fruit sugar, is the sweetest of the simple sugars. As the name implies, a large amount of fructose is found in fruits. While a certain amount of fructose enters directly into the blood from the digestive tract, it is sooner or later converted into glucose in the liver.

Oligosaccharides

Oligosaccharides consist of 2-10 linked monosaccharides. Disaccharides, or double sugars, are formed from two monosaccharides linked together.

Lactose (glucose + galactose) is the only type of sugar that is not found in plants, but is found in milk.
Maltose (glucose + glucose) - found in beer, cereals and germinating seeds.
Sucrose (glucose + fructose) - Known as table sugar, this is the most common disaccharide that enters the body with food. It is found in beet sugar, cane sugar, honey and maple syrup.

Monosaccharides and disaccharides form a group of simple sugars.

Polysaccharides

Polysaccharides are formed from 3 to 1000 monosaccharides linked together.

Types of polysaccharides:

- vegetable form of storage of carbohydrates. Starch exists in two forms: amylose or aminopectin. Amylose is a long, unbranched chain of spirally twisted glucose molecules, while amylopectin is a highly branched group of linked monosaccharides.
It is a non-starch structural polysaccharide found in plants and is usually difficult to digest. Examples of dietary fiber are cellulose and pectin.
Glycogen - 100-30,000 glucose molecules linked together. storage form of glucose.

Digestion and assimilation

Most carbohydrates we consume are in the form of starch. Starch digestion begins in the mouth under the action of salivary amylase. This process of digestion by amylase continues in the upper part of the stomach, then the action of amylase is blocked by stomach acid.

The digestion process is then completed in the small intestine with the help of pancreatic amylase. As a result of the breakdown of starch by amylase, the disaccharide maltose and short branched chains of glucose are formed.

These molecules, now in the form of maltose and short branched chain glucose, will then be broken down into individual glucose molecules by enzymes in the cells of the small intestine epithelium. The same processes occur during the digestion of lactose or sucrose. In lactose, the link between glucose and galactose is broken, resulting in the formation of two separate monosaccharides.

In sucrose, the link between glucose and fructose is broken, resulting in the formation of two separate monosaccharides. Individual monosaccharides then enter the blood through the intestinal epithelium. When ingesting monosaccharides (such as dextrose, which is glucose), no digestion is required and they are absorbed quickly.

Once in the blood, these carbohydrates, now in the form of monosaccharides, are used for their intended purpose. Since fructose and galactose are eventually converted to glucose, I will refer to all carbohydrates digested as "glucose" in the following.

Digested glucose

Assimilated, glucose is the main source of energy (during or immediately after a meal). This glucose is catabolized by the cells to provide energy for the formation. Glucose can also be stored in the form of glycogen in muscles and liver cells. But before that, it is necessary that glucose enters the cells. In addition, glucose enters the cell in different ways depending on the cell type.

To be absorbed, glucose must enter the cell. The transporters (Glut-1, 2, 3, 4 and 5) help her with this. In cells where glucose is the main source of energy, such as the brain, kidneys, liver, and red blood cells, glucose uptake occurs freely. This means that glucose can enter these cells at any time. In fat cells, the heart, and skeletal muscle, on the other hand, glucose uptake is regulated by the Glut-4 transporter. Their activity is controlled by the hormone insulin. In response to elevated blood glucose levels, insulin is released from the beta cells of the pancreas.

Insulin binds to a receptor on the cell membrane, which, through various mechanisms, leads to the translocation of Glut-4 receptors from intracellular storage to the cell membrane, allowing glucose to enter the cell. Skeletal muscle contraction also enhances translocation of the Glut-4 transporter.

When muscles contract, calcium is released. This increase in calcium concentration stimulates the translocation of GLUT-4 receptors, facilitating glucose uptake in the absence of insulin.

Although the effects of insulin and exercise on Glut-4 translocation are additive, they are independent. Once in the cell, glucose can be used to meet energy needs or synthesized into glycogen and stored for later use. Glucose can also be converted to fat and stored in fat cells.

Once in the liver, glucose can be used to meet the energy needs of the liver, stored as glycogen, or converted to triglycerides for storage as fat. Glucose is a precursor of glycerol phosphate and fatty acids. The liver converts excess glucose into glycerol phosphate and fatty acids, which are then combined to synthesize triglycerides.

Some of these formed triglycerides are stored in the liver, but most of them, along with proteins, are converted into lipoproteins and secreted into the blood.

Lipoproteins that contain much more fat than protein are called very low density lipoproteins (VLDL). These VLDLs are then transported through the blood to adipose tissue, where they will be stored as triglycerides (fats).

Accumulated glucose

Glucose is stored in the body as the polysaccharide glycogen. Glycogen is made up of hundreds of glucose molecules linked together and is stored in muscle cells (about 300 grams) and liver (about 100 grams).

The accumulation of glucose in the form of glycogen is called glycogenesis. During glycogenesis, glucose molecules are alternately added to an existing glycogen molecule.

The amount of glycogen stored in the body is determined by carbohydrate intake; a person on a low-carb diet will have less glycogen than a person on a high-carb diet.

To use stored glycogen, it must be broken down into individual glucose molecules in a process called glycogenolysis (lysis = breakdown).

Meaning of glucose

The nervous system and brain need glucose to function properly, as the brain uses it as its main fuel source. When there is insufficient supply of glucose as an energy source, the brain can also use ketones (by-products of incomplete breakdown of fats), but this is more likely to be considered as a fallback option.

Skeletal muscles and all other cells use glucose for their energy needs. When the required amount of glucose is not supplied to the body with food, glycogen is used. Once glycogen stores are depleted, the body is forced to find a way to get more glucose, which is achieved through gluconeogenesis.

Gluconeogenesis is the formation of new glucose from amino acids, glycerol, lactates, or pyruvate (all non-glucose sources). Muscle protein can be catabolized to provide amino acids for gluconeogenesis. When provided with the required amount of carbohydrates, glucose serves as a “protein saver” and can prevent the breakdown of muscle protein. Therefore, it is so important for athletes to consume enough carbohydrates.

Although there is no specific intake for carbohydrates, it is believed that 40-50% of calories consumed should come from carbohydrates. For athletes, this estimated rate is 60%.

What is ATP?
Adenosine triphosphate, the ATP molecule contains high-energy phosphate bonds and is used to store and release the energy needed by the body.

As with many other issues, people continue to argue about the amount of carbohydrates the body needs. For each individual, it should be determined based on a variety of factors, including: type of training, intensity, duration and frequency, total calories consumed, training goals, and the desired result based on body constitution.

Brief findings and conclusion

Carbohydrates = (CH2O)n, where n ranges from 3 to 7.
Monosaccharides are the "basic units" of carbohydrates
Oligosaccharides are made up of 2-10 linked monosaccharides
Disaccharides, or double sugars, are formed from two monosaccharides linked together, disaccharides include sucrose, lacrose and galactose.
Polysaccharides are formed from 3 to 1000 monosaccharides linked together; these include starch, dietary fiber and glycogen.
As a result of the breakdown of starch, maltose and short branched chains of glucose are formed.
To be absorbed, glucose must enter the cell. This is done by glucose transporters.
The hormone insulin regulates the operation of Glut-4 transporters.
Glucose can be used to form ATP, stored as glycogen or fat.
The recommended carbohydrate intake is 40-60% of total calories.

carbohydrate metabolism

a set of processes of transformation of monosaccharides and their derivatives, as well as homopolysaccharides, heteropolysaccharides and various carbohydrate-containing biopolymers (glycoconjugates) in the human and animal body. As a result, U. o. the body is supplied with energy (see Metabolism and energy) , processes of transfer of biological information and intermolecular interactions are carried out, reserve, structural, protective and other functions of carbohydrates are provided. Carbohydrate components of many substances, such as hormones (hormones) , enzymes (Enzymes) , transport glycoproteins are markers of these substances, thanks to which they are "recognized" by specific plasma and intracellular membranes.

Synthesis and transformation of glucose in the body. One of the most important carbohydrates is glucose. - is not only the main source of energy, but also a precursor of pentoses, uronic acids and hexose phosphate esters. It is formed from glycogen and food carbohydrates - sucrose, lactose, starch, dextrins. In addition, it is synthesized in the body from various non-carbohydrate precursors ( rice. one ). This process is called gluconeogenesis and plays an important role in maintaining homeostasis a . The process of gluconeogenesis involves many enzymes and enzyme systems localized in various cell organelles. Gluconeogenesis occurs mainly in the liver and kidneys.

There are two ways of glucose breakdown in the body: Glycolysis (phosphorolytic pathway, Embden-Meyerhof-Parnassus pathway) and pentose phosphate pathway (pentose pathway, hexose monophosphate shunt). Schematically, the pentose phosphate pathway looks like this: glucose-6-phosphate → 6-phosphate-gluconolactone → ribulose-5-phosphate → ribose-5-phosphate. In the course of the pentose phosphate pathway, the carbon chain is sequentially cleaved off at one carbon atom in the form of CO 2. While it plays an important role not only in energy metabolism, but also in the formation of intermediate products of lipid synthesis (Lipids) , the pentose phosphate pathway leads to the formation of ribose and deoxyribose, necessary for the synthesis of nucleic acids (Nucleic acids) (a number of coenzymes (Coenzymes) .

Synthesis and breakdown of glycogen. In the synthesis of glycogen, the main reserve polysaccharide of humans and higher animals, two enzymes are involved: glycogen synthetase (uridine diphosphate (UDP) glucose: glycogen-4α-glucosyltransferase), which catalyzes the formation of polysaccharide chains, and branching, which forms so-called branching bonds in glycogen molecules. Glycogen synthesis requires so-called seeds. Their role can be performed either with a different degree of polymerization, or protein precursors, to which glucose residues of uridine diphosphate glucose (UDP-glucose) are attached with the participation of a special enzyme glucoprotein synthetase.

The breakdown of glycogen is carried out by phosphorolytic () or hydrolytic pathways. is a cascade process involving a number of enzymes of the phosphorylase system - protein kinase, kinase b, phosphorylase b, phosphorylase a, amyl-1,6-glucosidase, glucose-6-phosphatase. In the liver, as a result of glycogenolysis, glucose is formed from glucose-6-phosphate due to the action of glucose-6-phosphatase, which is absent in muscles, where the conversion of glucose-6-phosphate leads to the formation of lactic acid (lactate). Hydrolytic (amylolytic) breakdown of glycogen ( rice. 2 ) is due to the action of a number of enzymes called amylases (Amylases) (α-glucosidases). α-, β- and γ-amylases are known. α-Glucosidases, depending on the localization in the cell, are divided into acidic (lysosomal) and neutral.

Synthesis and breakdown of carbohydrate-containing compounds. The synthesis of complex sugars and their derivatives occurs with the help of specific glycosyltransferases that catalyze the transfer of monosaccharides from donors - various glycosylnucleotides or lipid carriers to acceptor substrates, which can be a carbohydrate residue or a lipid, depending on the specificity of the transferases. The nucleotide residue is usually a diphosphonucleoside.

In humans and animals, there are many enzymes responsible for the conversion of some carbohydrates into others, both in the processes of glycolysis and gluconeogenesis, and in individual links of the pentose phosphate pathway.

Pathology of carbohydrate metabolism. An increase in blood glucose - may occur due to excessively intense gluconeogenesis or as a result of a decrease in the utilization of glucose by tissues, for example, in violation of the processes of its transport through cell membranes. A decrease in blood glucose - - can be a symptom of various diseases and pathological conditions, and the brain is especially vulnerable in this regard: irreversible impairment of its functions can be a consequence of hypoglycemia.

Genetically caused defects of U.'s enzymes. are the cause of many hereditary diseases (hereditary diseases) . Galactosemia can serve as an example of a genetically determined hereditary disorder of monosaccharide metabolism. , developing as a result of a defect in the synthesis of the enzyme galactose-1-phosphate uridyltransferase. Signs of galactosemia are also noted with a genetic defect in UDP-glucose-4-epimerase. Characteristic signs of galactosemia are hypoglycemia, the appearance and accumulation in the blood along with galactose of galactose-1-phosphate, as well as weight loss, fatty and cirrhosis of the liver, cataracts that develop at an early age, and psychomotor retardation. In severe galactosemia, children often die in the first year of life due to impaired liver function or reduced resistance to infections.

An example of hereditary intolerance to monosaccharides is, which is caused by a genetic defect in fructose phosphate aldolase and, in some cases, by a decrease in the activity of Fructose-1,6-diphosphate aldolase. characterized by damage to the liver and kidneys. The clinical picture is characterized by frequent, sometimes coma. Symptoms of the disease appear in the first months of life when children are transferred to mixed or artificial. Fructose loading causes severe hypoglycemia.

Diseases caused by defects in the metabolism of oligosaccharides mainly consist of a violation of the digestion and absorption of dietary carbohydrates, which occurs mainly in the small intestine. and low molecular weight, formed from starch and food glycogen under the action of α-amylase of saliva and pancreatic juice, milk and sucrose are broken down by disaccharidases (maltase, lactase and sucrase) to the corresponding monosaccharides mainly in the microvilli of the small intestine mucosa, and then, if the transport process monosaccharides are not broken, they occur. The absence or decrease in the activity of disaccharidases to the mucous membrane of the small intestine is the main cause of intolerance to the corresponding disaccharides, which often leads to damage to the liver and kidneys, is the cause of diarrhea, flatulence (see Malabsorption syndrome) . Especially severe symptoms are characterized by hereditary, usually found from the very birth of the child. For the diagnosis of sugar intolerance, exercise tests are usually used with the introduction of a carbohydrate per os on an empty stomach, the intolerance of which is suspected. A more accurate one can be made by biopsy of the intestinal mucosa and determination of the activity of disaccharidases in the obtained material. consists in the exclusion from food of foods containing the corresponding disaccharide. A greater effect is observed, however, with the appointment of enzyme preparations, which allows such patients to eat ordinary food. For example, in case of lactase deficiency, it is advisable to add an enzyme containing it to milk before eating it. The correct diagnosis of diseases caused by disaccharidase deficiency is extremely important. The most common diagnostic error in these cases is the establishment of a false diagnosis of dysentery, other intestinal infections, and antibiotics, which leads to a rapid deterioration in the condition of sick children and serious consequences.

Diseases caused by impaired glycogen metabolism constitute a group of hereditary enzymopathies, united under the name of glycogenoses (Glycogenoses) . Glycogenoses are characterized by excessive accumulation of glycogen in cells, which may also be accompanied by a change in the structure of the molecules of this polysaccharide. Glycogenoses are referred to as so-called storage diseases. Glycogenoses (glycogenic) are inherited in an autosomal recessive or sex-linked manner. An almost complete absence of glycogen in cells is noted with aglycogenosis, the cause of which is the complete absence or reduced activity of liver glycogen synthetase.

Diseases caused by a violation of the metabolism of various glycoconjugates, in most cases, are the result of congenital disorders of the breakdown of glycolipids, glycoproteins or glycosaminoglycans (mucopolysaccharides) in various organs. They are also storage diseases. Depending on which compound accumulates abnormally in the body, there are glycoproteinodes,. Many lysosomal glycosidases, which underlie hereditary disorders of carbohydrate metabolism, exist in various forms, the so-called multiple forms, or isoenzymes. may be caused by a defect in any one isoenzyme. For example. Tay-Sachs disease is a consequence of a defect in the form of AN-acetylhexosaminidase (hexosaminidase A), while a defect in the forms A and B of this enzyme leads to Sandhoff's disease.

Most accumulation diseases are extremely difficult, many of them are still incurable. in various diseases, accumulation can be similar, and, on the contrary, the same thing can manifest itself differently in different patients. Therefore, it is necessary in each case to establish an enzyme defect, which is detected mostly in leukocytes and fibroblasts of the skin of patients. Glycoconjugates or various synthetic ones are used as substrates. With various mucopolysaccharidoses (Mucopolysaccharidoses) , as well as in some other accumulation diseases (for example, with mannosidosis) are excreted in the urine in significant quantities differing in structure. The isolation of these compounds from the urine and their identification is carried out in order to diagnose storage diseases. Determination of enzyme activity in cultured cells isolated from amniotic fluid obtained by amniocentesis in case of suspected storage disease allows prenatal diagnosis.

At some diseases serious disturbances At. occur secondarily. An example of such a disease is diabetes mellitus. , caused either by damage to the β-cells of the pancreatic islets, or by defects in the structure of insulin itself or its receptors on the membranes of cells of insulin-sensitive tissues. Nutritional hyperglycemia leads to the development of obesity, which increases lipolysis and the use of non-esterified fatty acids (NEFA) as an energy substrate. This impairs the utilization of glucose in muscle tissue and stimulates gluconeogenesis. In turn, an excess of NEFA and insulin in the blood leads to an increase in the synthesis of triglycerides (see Fats) and Cholesterol in the liver and, accordingly, to an increase in the concentration of very low and low density lipoproteins (Lipoproteins) in the blood. One of the reasons contributing to the development of such severe complications in diabetes as cataracts, anglopathy and tissues is.

Features of carbohydrate metabolism in children. U.'s condition about. in children, it is normally determined by the maturity of the endocrine mechanisms of regulation and the functions of other systems and organs. In maintaining fetal homeostasis, an important role is played by the supply of glucose to it through the placenta. The amount of glucose passing through the placenta to the fetus is not constant, because. its concentration in the mother's blood can change several times during the day. Changes in the insulin/glucose ratio in the fetus can cause acute or long-term metabolic disorders. In the last third of the intrauterine period, the glycogen stores in the liver and muscles increase significantly in the fetus; during this period, glucogenolysis and gluconeogenesis are already essential for the fetus as a source of glucose.

Feature U. about. in the fetus and newborn, there is a high activity of glycolysis processes, which makes it possible to better adapt to hypoxia conditions. The intensity of glycolysis in newborns is 30-35% higher than in adults; in the first months after birth, it gradually decreases. The high intensity of glycolysis in newborns is indicated by a high content of lactate in the blood and urine and a higher activity of lactate dehydrogenase (Lactate dehydrogenase) in the blood than in adults. A significant part of the glucose in the fetus is oxidized along the pentose phosphate pathway.

Childbirth, changes in ambient temperature, the appearance of spontaneous breathing in newborns, an increase in muscle activity and increased brain activity increase energy consumption during childbirth and in the first days of life, leading to a rapid decrease in blood glucose. Through 4-6 h after birth, its content decreases to a minimum (2.2-3.3 mmol/l), remaining at this level for the next 3-4 days. Increased glucose uptake by tissues in newborns and the period of fasting after delivery lead to increased glycogenolysis and the use of reserve glycogen and fat. The store of glycogen in the liver of a newborn in the first 6 h life is sharply (about 10 times) reduced, especially with asphyxia (Asphyxia) and starvation. The content of glucose in the blood reaches the age norm in full-term newborns by the 10th-14th day of life, and in premature babies it is established only by the 1st-2nd month of life. In the intestines of newborns, enzymatic lactose (the main carbohydrate of food during this period) is somewhat reduced and increases in infancy. galactose in newborns is more intense than in adults.

Violations U. about. in children with various somatic diseases they are secondary and are associated with the influence of the main pathological process on this exchange. The lability of the mechanisms of regulation of carbohydrate and fat metabolism in early childhood creates the prerequisites for the occurrence of hypo- and hyperglycemic conditions, acetonemic vomiting. So, for example, violations of U. o. with pneumonia in young children, they are manifested by an increase in fasting blood concentrations of glucose and lactate, depending on the degree of respiratory failure. Carbohydrate intolerance is detected in obesity and is caused by changes in insulin secretion. In children with intestinal syndromes, a violation of the breakdown and absorption of carbohydrates is often detected, with celiac disease (see Celiac Disease), a flattening of the glycemic curve is noted after loading with starch, disaccharides and monosaccharides, and in young children with acute enterocolitis and a salt-deficient state, a tendency to hypoglycemia is observed during dehydration .

In the blood of older children, galactose, pentoses and disaccharides are normally absent, in infants they can appear in the blood after eating a meal rich in these carbohydrates, as well as with genetically determined abnormalities in the metabolism of the corresponding carbohydrates or carbohydrate-containing compounds; in the vast majority of cases, the symptoms of such diseases appear in children at an early age.

For early diagnosis of hereditary and acquired disorders U. o. in children, a staged examination system is used using the genealogical method (see Medical genetics) , various screening tests (see Screening) , as well as in-depth biochemical studies. At the first stage of the examination, glucose, fructose, sucrose, lactose are determined in the urine by qualitative and semi-quantitative methods, the pH value of feces is checked (Kala-azar) . Upon receipt of results that make one suspect pathologies) U. o., they proceed to the second stage of the examination: determining the content of glucose in the urine and blood on an empty stomach by quantitative methods, constructing glycemic and glucosuric curves, studying glycemic curves after differentiated sugar loads, determining the content of glucose in the blood after administration adrenaline, glucagon, leucine, butamide, cortisone, insulin; in some cases, direct determination of the activity of disaccharidases in the mucous membrane of the duodenum and small intestine and chromatographic identification of blood and urine carbohydrates are carried out. To detect disorders of digestion and absorption of carbohydrates, after establishing the pH value of feces, they determine to mono- and disaccharides with the obligatory measurement of sugar content in feces and their chromatographic identification before and after loading tests with carbohydrates. activity of U.'s enzymes of the lake, defect of synthesis (or decrease in activity) of which clinicians suspect.

For correction of the broken U. about. with a tendency to hyperglycemia, diet therapy with restriction of fats and carbohydrates is used. If necessary, prescribe insulin or other hypoglycemic drugs; drugs that increase blood glucose levels are canceled. With hypoglycemia, it is shown to be rich in carbohydrates and proteins.

During attacks of hypoglycemia, glucose, glucagon, are administered. In case of intolerance to certain carbohydrates, an individual diet is prescribed with the exclusion of the corresponding sugars from the food of patients. In cases of U.'s violations of the lake, which are secondary, treatment of the underlying disease is necessary.

Prevention of the expressed disturbances At. in children lies in their timely detection. At probability of hereditary pathology At. recommended Medical genetic counseling . The expressed adverse effect of decompensation of diabetes mellitus in pregnant women on U. o. in the fetus and newborn dictates the need for careful compensation of the disease in the mother throughout pregnancy and childbirth.

Bibliography: Widershine G.Ya. Biochemical bases of glycosidoses, M., 1980; functions of the child's body in normal and pathological conditions, ed. M.Ya. Studenikina and others, p. 33, M., 1978; Komarov F.I., Korovkin B.F. and Menshikov V.V. Biochemical research in the clinic, p. 407, L., 1981; Metzler, D., trans. from English, vol. 2, M., 1980; Nikolaev A.Ya. Biological chemistry, M., 1989; Rosenfeld E.L. and Popova I.A. Congenital disorders of glycogen metabolism, M., 1989; Handbook of functional diagnostics in pediatrics, ed. Yu.E. Veltishchev and N.S. Kislyak, p. 107, M., 1979.

the reaction of the formation of lactate from glucose-6-phosphate in the muscles in the absence of glucose-6-phosphatase activity "\u003e

Rice. 2. Scheme of breakdown in the body of glycogen to glucose; the numbers indicate the reactions catalyzed by the following enzymes: 1 - phosphorylase; 2 - amyl-1,6-glucosidase; 3 - phosphoglucomutase; 4 - glucose-6-phosphatase; 5 - α-amylase; 6 - neutral α-glucosidases; 7 - acid α-glucosidase α-amylase); the dotted line indicates the reaction of lactate formation from glucose-6-phosphate in the muscles in the absence of glucose-6-phosphatase activity.

1. Small medical encyclopedia. - M.: Medical Encyclopedia. 1991-96 2. First aid. - M.: Great Russian Encyclopedia. 1994 3. Encyclopedic dictionary of medical terms. - M.: Soviet Encyclopedia. - 1982-1984.

Carbohydrate metabolism is a set of processes of carbohydrate transformations in the human and animal body.

Process of transformations of carbohydrates (see) begins with their digestion in an oral cavity where there is a partial splitting of starch under the action of enzyme - amylase. They are mainly digested and absorbed in the small intestine, where (see) they are broken down with the help of monosaccharides (see) and then they are carried into the tissues and organs with the bloodstream, and most of them, mainly glucose, accumulate in the liver in the form of glycogen. Glucose with blood enters those organs or tissues where there is a need for it, and the rate of penetration of glucose into cells is determined by cell membranes. Glucose penetrates freely into liver cells, glucose penetration into muscle tissue cells is associated with energy consumption; during muscular work, the cell wall increases significantly. When needed, glycogen is converted by glycogenolysis to the phosphorylated form of glucose (phosphorus glucose). In cells, glucose can undergo transformation both anaerobically (glycolysis) and aerobically (pentose cycle). In the process of glycolysis, for each molecule of glucose that is broken down, 2 molecules of adenosine triphosphate (ATP) and 2 molecules of lactic acid are formed. If the tissues are sufficiently supplied with oxygen, then (an intermediate product of carbohydrate metabolism formed during the anaerobic breakdown of carbohydrates) is not reduced to lactic acid, but is oxidized in the tricarboxylic acid cycle (see Biological oxidation) to and H 2 O with the accumulation of energy in the form of ATP in the system oxidizing (see).

When glucose is oxidized in the pentose cycle, reduced nicotinamide adenine nucleotide phosphate is formed, which is necessary for reductive syntheses. In addition, the intermediate products of the pentose cycle are the material for the synthesis of many important compounds.

The regulation of carbohydrate metabolism is mainly carried out by hormones and the central nervous system. Glucocorticosteroids (cortisone,) slow down the rate of transport of glucose into tissue cells, insulin (see) accelerates it; adrenaline (see) stimulates the process of sugar formation from glycogen in the liver. The cerebral cortex also has a certain role in the regulation of carbohydrate metabolism, since psychogenic factors increase the formation of sugar in the liver and cause. The state of carbohydrate metabolism can be judged by the content of sugar in the blood (normally 70-120 mg%). With a sugar load, this value increases, but then quickly reaches the norm. Carbohydrate metabolism disorders occur in various diseases. So, with a lack of insulin occurs. A decrease in the activity of one of the enzymes of carbohydrate metabolism - muscle phosphorylase - leads to muscular dystrophy. See also Metabolism and Energy.

Carbohydrates or glucides, as well as fats and proteins, are the main organic compounds of our body. Therefore, if you want to study the issue of carbohydrate metabolism in the human body, we recommend that you first familiarize yourself with the chemistry of organic compounds. If you want to know what carbohydrate metabolism is and how it occurs in the human body, without going into details, then our article is for you. We will try to tell in a simpler way about carbohydrate metabolism in our body.

Carbohydrates are a large group of substances, which mainly consists of hydrogen, oxygen and carbon. Some complex carbohydrates also contain sulfur and nitrogen.

All living organisms on our planet are made up of carbohydrates. Plants consist of almost 80% of them, animals and humans contain much less carbohydrates. Carbohydrates are mainly contained in the liver (5-10%), muscles (1-3%), brain (less than 0.2%).

We need carbohydrates as a source of energy. When oxidizing just 1 gram of carbohydrates, we get 4.1 kcal of energy. In addition, some complex carbohydrates are reserve nutrients, while fiber, chitin and hyaluronic acid give tissues strength. Carbohydrates are also one of the building blocks of more complex molecules such as nucleic acid, glycolipids, etc. Without the participation of carbohydrates, the oxidation of proteins and fats is impossible.

Types of carbohydrates

Depending on how the carbohydrate is able to decompose into simpler carbohydrates using hydrolysis (i.e., splitting with the participation of water), they are classified into monosaccharides, oligosaccharides and polysaccharides. Monosaccharides are not hydrolyzed and are considered simple carbohydrates consisting of 1 sugar particle. This is, for example, glucose or fructose. Oligosaccharides are hydrolyzed to form a small number of monosaccharides, and polysaccharides are hydrolyzed into many (hundreds, thousands) of monosaccharides.

Glucose is not digested and is absorbed unchanged into the blood from the intestine.

Disaccharides are distinguished from the class of oligosaccharides - for example, cane or beet sugar (sucrose), milk sugar (lactose).

Polysaccharides are carbohydrates that are made up of many monosaccharides. These are, for example, starch, glycogen, fiber. Unlike monosaccharides and disaccharides, which are absorbed almost immediately in the intestines, polysaccharides are digested for a long time, which is why they are called heavy or complex. Their breakdown takes a long time, which allows you to maintain blood sugar levels in a stable position, without the insulin spikes that simple carbohydrates cause.

The main digestion of carbohydrates occurs in the juice of the small intestine.

The supply of carbohydrates in the form of glycogen in the muscles is very small - about 0.1% of the weight of the muscle itself. And since the muscles cannot work without carbohydrates, they need a regular supply of them through the blood. In the blood, carbohydrates are in the form of glucose, the content of which ranges from 0.07 to 0.1%. The main stores of carbohydrates in the form of glycogen are found in the liver. A person weighing 70 kg has about 200 grams (!) of carbohydrates in the liver. And when the muscles “eat up” all the glucose from the blood, glucose from the liver enters it again (previously, glycogen in the liver is split into glucose). Stocks in the liver are not eternal, so you need to replenish it with food. If carbohydrates are not supplied with food, then the liver forms glycogen from fats and proteins.

When a person is engaged in physical work, the muscles deplete all glucose reserves and a condition called hypoglycemia occurs - as a result, the work of the muscles themselves and even nerve cells is disrupted. That is why it is important to follow the right diet, especially nutrition before and after training.

Regulation of carbohydrate metabolism in the body

As follows from the above, all carbohydrate metabolism comes down to blood sugar levels. Blood sugar levels depend on how much glucose enters the bloodstream and how much glucose is removed from it. The entire carbohydrate metabolism depends on this ratio. Sugar in the blood comes from the liver and intestines. The liver only breaks down glycogen into glucose if blood sugar levels drop. These processes are regulated by hormones.

A decrease in blood sugar levels is accompanied by the release of the hormone adrenaline - it activates the liver enzymes that are responsible for the entry of glucose into the blood.

Carbohydrate metabolism is also regulated by two pancreatic hormones - insulin and glucagon. Insulin is responsible for transporting glucose from the blood to the tissues. And glucagon is responsible for the breakdown of glucagon in the liver into glucose. Those. glucagon raises blood sugar, while insulin lowers it. Their action is interconnected.

Of course, if the blood sugar level is too high, and the liver and muscles are saturated with glycogen, then insulin sends the “unnecessary” material to the fat depot - i.e. stores glucose as fat.

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SAEI SPO RT "Almetyevsk Medical College"

in anatomy on the topic: "Carbohydrate metabolism"

Completed by: Khairullin R.R.

Checked by: Galliamova L.Kh

Almetyevsk 2014

In the human body, up to 60% of the energy is satisfied by carbohydrates. As a result, the energy exchange of the brain is almost exclusively carried out by glucose. Carbohydrates also perform a plastic function. They are part of complex cellular structures (glycopeptides, glycoproteins, glycolipids, lipopolysaccharides, etc.). Carbohydrates are divided into simple and complex. The latter, when split in the digestive tract, form simple monosaccharides, which then enter the blood from the intestines. Carbohydrates enter the body mainly with plant foods (bread, vegetables, cereals, fruits) and are deposited mainly in the form of glycogen in the liver and muscles. The amount of glycogen in the body of an adult is about 400 g. However, these reserves are easily depleted and are used? Mainly for the urgent needs of energy metabolism.

The process of formation and accumulation of glycogen is regulated by the pancreatic hormone insulin. The process of splitting glycogen to glucose occurs under the influence of another pancreatic hormone - glucagon.

The content of glucose in the blood, as well as glycogen stores, are also regulated by the central nervous system. Nervous influence from the centers of carbohydrate metabolism comes to the organs through the autonomic nervous system. In particular, impulses coming from the centers along the sympathetic nerves directly increase the breakdown of glycogen in the liver and muscles, as well as the release of adrenaline from the adrenal glands. The latter promotes the conversion of glycogen into glucose and enhances oxidative processes in cells. The hormones of the adrenal cortex, the middle lobe of the pituitary gland and the thyroid gland also take part in the regulation of carbohydrate metabolism.

The optimal amount of carbohydrates per day is about 500 g, but this value, depending on the energy needs of the body, can vary significantly. It must be borne in mind that in the body the processes of metabolism of carbohydrates, fats and proteins are interconnected, their transformations are possible within certain limits. The fact is that the intermediate exchange of carbohydrates, proteins and fats forms common intermediate substances for all exchanges. The main product of the metabolism of proteins, fats and carbohydrates is acetylcoenzyme A. With its help, the metabolism of proteins, fats and carbohydrates is reduced to a cycle of tricarboxylic acids, in which about 70% of the total energy of transformations is released as a result of oxidation.

The end products of metabolism are a small number of simple compounds. Nitrogen is released in the form of nitrogen-containing compounds (mainly urea and ammonia), carbon - in the form of CO2, hydrogen - in the form of H2O.

The main source of carbohydrate metabolism is glycogen, which is easily oxidized during muscle work. Only when the store of glycogen in the muscles is fully used does the direct oxidation of glucose delivered with the blood occur. After muscle work, the supply of glycogen in the muscles and in the liver is restored due to monosaccharides absorbed in the alimentary canal and formed during the breakdown of proteins and fats.

Carbohydrates are easily oxidized to carbon dioxide and water, but the breakdown of carbohydrates in the body can also occur without oxygen with the formation of lactic acid (glycolysis). Of great importance is the anoxic breakdown of carbohydrates with the participation of phosphoric acid - phosphorylation.

The amount of glucose in the blood is maintained due to its intake with food at the level of 0.1%, and with an increase in this level to 0.15%, it is excreted in the urine. The need for carbohydrates depends mainly on energy costs. Carbohydrates should make up about 56% of the energy of the daily diet. The average daily requirement of an adult is 400-500 g, and for manual workers - 700-1000 g, increasing depending on the intensity of muscle work. The net carbohydrate is sugar. A large amount of carbohydrates is found in plant foods, for example, in rye bread about 45% carbohydrates, wheat bread - 50%, buckwheat - 64%, semolina - 70%, rice - 72%, potatoes - 20%.

carbohydrate metabolism-- a set of processes of transformation of monosaccharides and their derivatives, as well as homopolysaccharides, heteropolysaccharides and various carbohydrate-containing biopolymers (glycoconjugates) in the human and animal body. As a result, U. o. the body is supplied with energy (cf. Metabolism and energy ), processes of transfer of biological information and intermolecular interactions are carried out, reserve, structural, protective and other functions of carbohydrates are provided. Carbohydrate components of many substances, for example hormones , enzymes , transport glycoproteins are markers of these substances, due to which they are "recognized" by specific receptors of plasma and intracellular membranes.

Synthesis and transformation of glucose in the body. One of the most important carbohydrates is glucose - is not only the main source of energy, but also a precursor of pentoses, uronic acids and hexose phosphoric esters. Glucose is formed from glycogen and food carbohydrates - sucrose, lactose, starch, dextrins. In addition, glucose is synthesized in the body from various non-carbohydrate precursors. This process is called gluconeogenesis and plays an important role in maintaining homeostasis . The process of gluconeogenesis involves many enzymes and enzyme systems localized in various cell organelles. Gluconeogenesis occurs mainly in the liver and kidneys.

There are two ways of breaking down glucose in the body: glycolysis (phosphorolytic pathway, Embden-Meyerhof-Parnassus pathway) and pentose phosphate pathway (pentose pathway, hexose monophosphate shunt). Schematically, the pentose phosphate pathway looks like this: glucose-6-phosphate 6-phosphate-gluconolactone ribulose-5-phosphate ribose-5-phosphate. In the course of the pentose phosphate pathway, successive cleavage from the carbon chain of sugar occurs at one carbon atom in the form of CO 2. While glycolysis plays an important role not only in energy metabolism, but also in the formation of intermediate synthesis products lipids , the pentose phosphate pathway leads to the formation of ribose and deoxyribose, necessary for the synthesis nucleic acids (series coenzymes .

Synthesis and breakdown of glycogen. In the synthesis of glycogen, the main reserve polysaccharide of humans and higher animals, two enzymes are involved: glycogen synthetase (uridine diphosphate (UDP) glucose: glycogen-4?-glucosyltransferase), catalyzing the formation of polysaccharide chains, and a branching enzyme that forms so-called bonds in glycogen molecules branching. Glycogen synthesis requires so-called seeds. Their role can be played either by glucosides with various degrees of polymerization, or by protein precursors, to which, with the participation of a special enzyme glucoprotein synthetase, glucose residues of uridine diphosphate glucose (UDP-glucose) are added.

The breakdown of glycogen is carried out by phosphorolytic (glycogenolysis) or hydrolytic pathways. Glycogenolysis is a cascade process involving a number of enzymes of the phosphorylase system - protein kinase, phosphorylase b kinase, phosphorylase b, phosphorylase a, amyl-1,6-glucosidase, glucose-6-phosphatase. In the liver, as a result of glycogenolysis, glucose is formed from glucose-6-phosphate due to the action of glucose-6-phosphatase, which is absent in muscles, where the conversion of glucose-6-phosphate leads to the formation of lactic acid (lactate). Hydrolytic (amylolytic) breakdown of glycogen is due to the action of a number of enzymes called amylase (glucosidases). Glucosidases, depending on their localization in the cell, are divided into acidic (lysosomal) and neutral.

Synthesis and breakdown of carbohydrate-containing compounds. The synthesis of complex sugars and their derivatives occurs with the help of specific glycosyltransferases that catalyze the transfer of monosaccharides from donors - various glycosylnucleotides or lipid carriers to acceptor substrates, which can be a carbohydrate residue, polyp peptide or lipid depending on the specificity of transferases. The nucleotide residue is usually a diphosphonucleoside.

Enzymatic cleavage of carbohydrate-containing compounds occurs mainly hydrolytically with the help of glycosidases that cleave carbohydrate residues (exoglycosidases) or oligosaccharide fragments (endoglycosidases) from the corresponding glycoconjugates. Glycosidases are extremely specific enzymes. Depending on the nature of the monosaccharide, the configuration of its molecule (their D or L-isomers) and the type of hydrolysable bond, D-mannosidases, L-fucosidases, D-galactosidases, etc. are distinguished. Glycosidases are localized in various cellular organelles; many of them are localized in lysosomes. Lysosomal (acidic) glycosidases differ from neutral ones not only in their localization in cells, the optimal pH value and molecular weight for their action, but also in electrophoretic mobility and a number of other physicochemical properties.

Glycosidases play an important role in various biological processes; they can, for example, affect the specific growth of transformed cells, the interaction of cells with viruses, etc.

There is evidence of the possibility of non-enzymatic glycosylation of proteins in vivo, such as hemoglobin, lens proteins, collagen. There is evidence that non-enzymatic glycosylation (glycation) plays an important pathogenetic role in certain diseases (diabetes diabetes e, galactosemia, etc.).

Carbohydrate transport. Digestion of carbohydrates begins in the oral cavity with the participation of hydrolytic enzymes saliva . Hydrolysis by enzymes of saliva continues in the stomach (fermentation of carbohydrates in the food bolus is prevented by hydrochloric acid in gastric juice). In the duodenum, food polysaccharides (starch, glycogen, etc.) and sugars (oligo- and disaccharides) are broken down with the participation of glucosidases and other glycosidases of pancreatic juice to monosaccharides, which are absorbed into the blood in the small intestine. The rate of absorption of carbohydrates is different, glucose and galactose are absorbed faster, fructose, mannose and other sugars are absorbed more slowly.

The transport of carbohydrates through the epithelial cells of the intestine and the entry into the cells of peripheral tissues is carried out using special transport systems, the function of which is also the transfer of sugar molecules through cell membranes. There are special carrier proteins - permeases (translocases), specific for sugars and their derivatives. Carbohydrate transport can be passive or active. In passive transport, the transport of carbohydrates is carried out in the direction of the concentration gradient, so that equilibrium is reached when the concentrations of sugar in the intercellular substance or intercellular fluid and inside the cells are aligned. Passive transport of sugars is characteristic of human erythrocytes. With active transport, carbohydrates can accumulate in cells and their concentration inside the cells becomes higher than in the fluid surrounding the cells. It is assumed that the active absorption of sugars by cells differs from the passive one in that the latter is a Na + -independent process. In humans and animals, active transport of carbohydrates occurs mainly in the epithelial cells of the intestinal mucosa and in the convoluted tubules (proximal parts of the nephron) of the kidneys.

The regulation of carbohydrate metabolism is carried out with the participation of very complex mechanisms that can influence the induction or suppression of the synthesis of various enzymes U. o. or contribute to the activation or inhibition of their action. Insulin , catecholamines , glucagon, somatotropic and steroid hormones have a different, but very pronounced effect on various processes of carbohydrate metabolism. For example, insulin promotes the accumulation of glycogen in the liver and muscles by activating the enzyme glycogen synthetase, and inhibits glycogenolysis and gluconeogenesis. Insulin antagonist - glucagon stimulates glycogenolysis. Adrenaline, stimulating the action of adenylate cyclase, affects the entire cascade of phosphorolysis reactions. Gonadotropic hormones activate glycogenolysis in the placenta. Glucocorticoid hormones stimulate the process of gluconeogenesis. Somatotropic hormone affects the activity of enzymes of the pentose phosphate pathway and reduces the utilization of glucose by peripheral tissues. Acetyl-CoA and reduced nicotinamide adenine dinucleotide are involved in the regulation of gluconeogenesis. An increase in the content of fatty acids in the blood plasma inhibits the activity of key enzymes of glycolysis. In the regulation of enzymatic reactions U. o. an important goal is played by Ca 2+ ions, directly or with the participation of hormones, often in connection with a special Ca 2+ -binding protein - calmodulin. In the regulation of the activity of many enzymes, the processes of their phosphorylation - dephosphorylation are of great importance. In an organism there is a direct communication between At. the lake. and protein metabolism (see nitrogen metabolism ), lipids (see Fat metabolism ) and minerals (see Mineral exchange ).

Pathology of carbohydrate metabolism. Increase in blood glucose -- hyperglycemia can occur due to excessively intensive gluconeogenesis or as a result of a decrease in the ability of glucose utilization by tissues, for example, in violation of the processes of its transport through cell membranes. A decrease in blood glucose - hypoglycemia - can be a symptom of various diseases and pathological conditions, and the brain is especially vulnerable in this regard: irreversible impairment of its functions can be a consequence of hypoglycemia.

Genetically caused defects of U.'s enzymes. are the cause of many hereditary diseases . An example of a genetically determined hereditary disorder of monosaccharide metabolism is galactosemia , developing as a result of a defect in the synthesis of the enzyme galactose-1-phosphate uridyltransferase. Signs of galactosemia are also noted with a genetic defect in UDP-glucose-4-epimerase. The characteristic features of galactosemia are hypoglycemia, galactosuria, the appearance and accumulation in the blood along with galactose of galactose-1-phosphate, as well as weight loss, fatty dystrophy and cirrhosis liver, jaundice, cataract, developing at an early age, delayed psychomotor development. In severe galactosemia, children often die in the first year of life due to impaired liver function or reduced resistance to infections.

An example of hereditary monosaccharide intolerance is fructose intolerance, which is caused by a genetic defect in fructose phosphate aldolase and, in some cases, by a decrease in fructose-1,6-diphosphate aldolase activity. The disease is characterized by damage to the liver and kidneys. The clinical picture is characterized by convulsions, frequent vomiting, and sometimes a coma. Symptoms of the disease appear in the first months of life when children are transferred to mixed or artificial nutrition. Fructose loading causes severe hypoglycemia.

Diseases caused by defects in the metabolism of oligosaccharides mainly consist in a violation of the breakdown and absorption of dietary carbohydrates, which occurs mainly in the small intestine. Maltose and low molecular weight dextrins formed from food starch and glycogen under the action of salivary amylase and pancreatic juice, milk lactose and sucrose are broken down by disaccharidases (maltase, lactase and sucrase) to the corresponding monosaccharides mainly in the microvilli of the small intestine mucosa, and then, if the process transport of monosaccharides is not disturbed, their absorption occurs. The absence or decrease in the activity of disaccharidases to the mucous membrane of the small intestine is the main cause of intolerance to the corresponding disaccharides, which often leads to damage to the liver and kidneys, is the cause of diarrhea, flatulence a (see Malabsorption syndrome ). Particularly severe symptoms are characterized by hereditary lactose intolerance, which is usually found from the very birth of the child. For the diagnosis of sugar intolerance, stress tests are usually used with the introduction of a carbohydrate per os on an empty stomach, the intolerance of which is suspected. A more accurate diagnosis can be made by biopsy of the intestinal mucosa and determination of the activity of disaccharidases in the obtained material. Treatment consists in the exclusion from food of foods containing the corresponding disaccharide. A greater effect is observed, however, with the appointment of enzyme preparations, which allows such patients to eat ordinary food. For example, in the case of lactase deficiency, it is desirable to add an enzyme preparation containing lactase to milk before eating it. The correct diagnosis of diseases caused by disaccharidase deficiency is extremely important. The most common diagnostic error in these cases is the establishment of a false diagnosis of dysentery, other intestinal infections, and antibiotic treatment, which leads to a rapid deterioration in the condition of sick children and serious consequences.

Diseases caused by impaired glycogen metabolism constitute a group of hereditary enzymopathies, united under the name glycogenoses . Glycogenoses are characterized by excessive accumulation of glycogen in cells, which may also be accompanied by a change in the structure of the molecules of this polysaccharide. Glycogenoses are referred to as so-called storage diseases. Glycogenoses (glycogenic disease) are inherited in an autosomal recessive or sex-linked manner. An almost complete absence of glycogen in cells is noted with aglycogenosis, the cause of which is the complete absence or reduced activity of liver glycogen synthetase.

Diseases caused by a violation of the metabolism of various glycoconjugates, in most cases, are the result of congenital disorders of the breakdown of glycolipids, glycoproteins or glycosaminoglycans (mucopolysaccharides) in various organs. They are also storage diseases. Depending on which compound accumulates abnormally in the body, glycolipidoses, glycoproteinodes, and mucopolysaccharidoses are distinguished. Many lysosomal glycosidases, the defect of which underlies hereditary disorders of carbohydrate metabolism, exist in various forms,

so-called multiple forms, or isoenzymes. The disease can be caused by a defect in any one isoenzyme. For example. Tay-Sachs disease is a consequence of a defect in the form of AN-acetylhexosaminidase (hexosaminidase A), while a defect in the forms A and B of this enzyme leads to Sandhoff's disease.

Most accumulation diseases are extremely difficult, many of them are still incurable. The clinical picture in various storage diseases may be similar, and, on the contrary, the same disease may manifest itself differently in different patients. Therefore, it is necessary in each case to establish an enzyme defect, which is detected mostly in leukocytes and fibroblasts of the skin of patients. Glycoconjugates or various synthetic glycosides are used as substrates. With various mucopolysaccharidoses , as well as in some other storage diseases (for example, with mannosidosis), significant amounts of oligosaccharides differing in structure are excreted in the urine. The isolation of these compounds from the urine and their identification is carried out in order to diagnose storage diseases. Determination of enzyme activity in cultured cells isolated from amniotic fluid obtained by amniocentesis in case of suspected storage disease allows prenatal diagnosis.

At some diseases serious disturbances At. occur secondarily. An example of such a disease is diabetes mellitus , caused either by damage to the cells of the pancreatic islets, or by defects in the structure of insulin itself or its receptors on the cell membranes of insulin-sensitive tissues. Alimentary hyperglycemia and hyperinsulinemia lead to the development of obesity, which increases lipolysis and the use of non-esterified fatty acids (NEFA) as an energy substrate. This impairs the utilization of glucose in muscle tissue and stimulates gluconeogenesis. In turn, an excess of NEFA and insulin in the blood leads to an increase in the synthesis of triglycerides in the liver (see. Fats ) and cholesterol and, consequently, to an increase in the concentration in the blood lipoproteins very low and low density. One of the reasons contributing to the development of such severe complications in diabetes e, how cataract, nephropathy, anglopathia and tissue hypoxia, is non-enzymatic glycosylation of proteins.

Feature U. about. in the fetus and newborn, there is a high activity of glycolysis processes, which makes it possible to better adapt to hypoxia conditions. The intensity of glycolysis in newborns is 30--35% higher than in adults; in the first months after birth, it gradually decreases. The high intensity of glycolysis in newborns is evidenced by a high content of lactate in the blood and urine and a higher activity than in adults. lactate dehydrogenase in blood. A significant part of the glucose in the fetus is oxidized along the pentose phosphate pathway.

Birth stress, changes in ambient temperature, the appearance of spontaneous breathing in newborns, increased muscle activity and increased brain activity increase energy expenditure during childbirth and in the first days of life, leading to a rapid decrease in blood glucose. Through 4--6 h after birth, its content decreases to a minimum (2.2--3.3 mmol/l), remaining at this level for the next 3--4 days. Increased tissue glucose uptake in newborns and fasting after delivery lead to increased glycogenolysis and use of reserve glycogen and fat. The store of glycogen in the liver of a newborn in the first 6 h life is sharply (about 10 times) reduced, especially when asphyxia and starvation. The content of glucose in the blood reaches the age norm in full-term newborns by the 10th - 14th day of life, and in premature babies it is established only by the 1st - 2nd month of life. In the intestines of newborns, enzymatic hydrolysis of lactose (the main carbohydrate of food during this period) is somewhat reduced and increases in infancy. The exchange of galactose in newborns is more intense than in adults.

Violations U. about. in children with various somatic diseases are secondary in nature and are associated with the influence of the underlying pathological process on this type of metabolism.

The lability of the mechanisms of regulation of carbohydrate and fat metabolism in early childhood creates the prerequisites for the occurrence of hypo- and hyperglycemic conditions, acetonemic vomiting. So, for example, violations of U. o. with pneumonia in young children, they are manifested by an increase in fasting blood glucose and lactate concentrations, depending on the degree of respiratory failure. Carbohydrate intolerance is detected in obesity and is caused by changes in insulin secretion. In children with intestinal syndromes, a violation of the breakdown and absorption of carbohydrates is often detected, with celiac disease (see. celiac disease ) note a flattening of the glycemic curve after a load of starch, disaccharides and monosaccharides, and in young children with acute enterocolitis and a salt-deficient state with dehydration, a tendency to hypoglycemia is observed.

For early diagnosis of hereditary and acquired disorders U. o. in children, a staged examination system is used using the genealogical method (see. medical genetics ), various screening tests (see Screening ), as well as in-depth biochemical studies. At the first stage of the examination, glucose, fructose, sucrose, lactose are determined in the urine by qualitative and semi-quantitative methods, the pH value is checked feces . Upon receipt of results that make one suspect pathologies) U. o., they proceed to the second stage of the examination: determining the glucose content in the urine and blood on an empty stomach by quantitative methods, constructing glycemic and glucosuric curves, studying glycemic curves after differentiated sugar loads, determining the content of glucose in the blood after administration of adrenaline, glucagon, leucine, butamide, cortisone, insulin; in some cases, direct determination of the activity of disaccharidases in the mucous membrane of the duodenum and small intestine and chromatographic identification of blood and urine carbohydrates are carried out. To detect violations of the digestion and absorption of carbohydrates, after establishing the pH value of the feces, tolerance to mono- and disaccharides is determined with the obligatory measurement of the sugar content in the feces and their chromatographic identification before and after loading tests with carbohydrates. If enzymopathy is suspected (see. Fermentopathies ) in blood and fabrics define activity of enzymes U. of the lake, defect of synthesis (or decrease in activity) of which clinicians suspect.

For correction of the broken U. about. with a tendency to hyperglycemia, diet therapy with restriction of fats and carbohydrates is used. If necessary, prescribe insulin or other hypoglycemic drugs; drugs that increase blood glucose levels are canceled. With hypoglycemia, a diet rich in carbohydrates and proteins is indicated. carbohydrate metabolism man muscular

During attacks of hypoglycemia, glucose, glucagon, adrenaline are administered. In case of intolerance to certain carbohydrates, an individual diet is prescribed with the exclusion of the corresponding sugars from the food of patients. In cases of U.'s violations of the lake, which are secondary, treatment of the underlying disease is necessary.

Prevention of the expressed disturbances At. in children lies in their timely detection. At probability of hereditary pathology At. recommended medical genetic counseling . Pronounced adverse effects of decompensation of sugar diabetes and at pregnant women on U. about. in the fetus and newborn dictates the need for careful compensation of the disease in the mother throughout pregnancy and childbirth.

Bibliographeraphia

1. Wiederschein G.Ya. Biochemical bases of glycosidoses, M., 1980;

2. Hormonal regulation of the functions of the child's body in normal and pathological conditions, ed. M.Ya. Studenikina and others, p. 33, M., 1978;

3. Komarov F.I., Korovkin B.F. and Menshikov V.V. Biochemical research in the clinic, p. 407, L., 1981;

4. Metzler D. Biochemistry, trans. from English, vol. 2, M., 1980;

5. Nikolaev A.Ya. Biological chemistry, M., 1989;

6. Rosenfeld E.L. and Popova I.A. Congenital disorders of glycogen metabolism, M., 1989;

7. Handbook of functional diagnostics in pediatrics, ed. Yu.E. Veltishchev and N.S. Kislyak, p. 107, M., 1979.

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