Violation of carbohydrate metabolism. Carbohydrate metabolism Pentosuria, fructosuria, galactosuria

carbohydrate metabolism is responsible for the process of assimilation of carbohydrates in the body, their breakdown with the formation of intermediate and final products, as well as the formation of compounds that are not carbohydrates, or the transformation of simple carbohydrates into more complex ones. The main role of carbohydrates is determined by their energy function.

blood glucose is the direct source of energy in the body. The speed of its decomposition and oxidation, as well as the possibility of rapid extraction from the depot, provide an emergency mobilization of energy resources with rapidly increasing energy costs in cases of emotional arousal, with intense muscle loads.

At decrease in glucose levels develop in the blood

convulsions;

loss of consciousness;

vegetative reactions (increased sweating, changes in the lumen of skin vessels).

This condition is called "hypoglycemic coma". The introduction of glucose into the blood quickly eliminates these disorders.

Carbohydrate metabolism in the human body consists of the following processes:

Cleavage in the digestive tract of poly- and disaccharides coming with food to monosaccharides, further absorption of monosaccharides from the intestine into the blood.

Synthesis and breakdown of glycogen in tissues (glycogenesis and glycogenolysis).

Glycolysis (breakdown of glucose).

Anaerobic pathway of direct glucose oxidation (pentose cycle).

Interconversion of hexoses.

Anaerobic metabolism of pyruvate.

Gluconeogenesis is the formation of carbohydrates from non-carbohydrate foods.

Carbohydrate metabolism disorders

Absorption of carbohydrates is disturbed in case of insufficiency of amylolytic enzymes of the gastrointestinal tract (pancreatic juice amylase). At the same time, carbohydrates supplied with food are not broken down into monosaccharides and are not absorbed. As a result, the patient develops carbohydrate starvation.

Absorption of carbohydrates also suffers in violation of glucose phosphorylation in the intestinal wall, which occurs during inflammation of the intestine, in case of poisoning with poisons that block the hexokinase enzyme (phloridzin, monoiodoacetate). There is no phosphorylation of glucose in the intestinal wall and it does not enter the blood.

Carbohydrate absorption is particularly easily impaired in infants, who have not yet fully developed digestive enzymes and enzymes that provide phosphorylation and dephosphorylation.

Causes of impaired carbohydrate metabolism due to impaired hydrolysis and absorption of carbohydrates:

hypoxia

violation of liver function - a violation of the formation of glycogen from lactic acid - acidosis (hyperlaccidemia).

hypovitaminosis B1.

Violation of the synthesis and breakdown of glycogen

Glycogen synthesis can change towards a pathological increase or decrease. Increased breakdown of glycogen occurs when the central nervous system is excited. Impulses along the sympathetic pathways go to the glycogen depot (liver, muscles) and activate glycogenolysis and glycogen mobilization. In addition, as a result of excitation of the central nervous system, the function of pituitary, the medulla of the adrenal glands, the thyroid gland, whose hormones stimulate the breakdown of glycogen.

An increase in glycogen breakdown with a simultaneous increase in glucose consumption by muscles occurs during heavy muscle work. A decrease in glycogen synthesis occurs during inflammatory processes in the liver: hepatitis, during which its glycogen-educational function is disrupted.

With a lack of glycogen, tissue energy switches to fat and protein metabolism. Energy production from fat oxidation requires a lot of oxygen; otherwise, ketone bodies accumulate in excess and intoxication occurs. The formation of energy at the expense of proteins leads to the loss of plastic material. Glycogenosis This is a violation of glycogen metabolism, accompanied by a pathological accumulation of glycogen in the organs.

Gierke's disease glycogenosis, caused by a congenital deficiency of glucose-6-phosphatase, an enzyme found in the cells of the liver and kidneys.

Glycogenosis with congenital deficiency of α-glucosidase. This enzyme cleaves glucose residues from glycogen molecules and breaks down maltose. It is contained in lysosomes and is uncoupled from cytoplasmic phosphorylase.

In the absence of α-glucosidase, glycogen accumulates in lysosomes, which pushes the cytoplasm, fills the entire cell and destroys it. The content of glucose in the blood is normal. Glycogen is stored in the liver, kidneys, and heart. Metabolism in the myocardium is disturbed, the heart increases in size. Sick children die early from heart failure.

Intermediate carbohydrate metabolism disorders

The violation of the intermediate metabolism of carbohydrates can lead to:

Hypoxic conditions(for example, with respiratory or circulatory failure, with anemia), the anaerobic phase of carbohydrate conversion predominates over the aerobic phase. There is an excessive accumulation in the tissues and blood of lactic and pyruvic acids. The content of lactic acid in the blood increases several times. Acidosis occurs. Enzymatic processes are disturbed. Decreased production of ATP.

liver function disorders, where normally part of the lactic acid is resynthesized into glucose and glycogen. With liver damage, this resynthesis is disrupted. Hyperlaccidemia and acidosis develop.

Hypovitaminosis B1. The oxidation of pyruvic acid is disturbed, since vitamin B1 is part of the coenzyme involved in this process. Pyruvic acid accumulates in excess and partially passes into lactic acid, the content of which also increases. In violation of the oxidation of pyruvic acid, the synthesis of acetylcholine decreases and the transmission of nerve impulses is disrupted. The formation of acetyl coenzyme A from pyruvic acid is reduced. Pyruvic acid is a pharmacological poison for nerve endings. With an increase in its concentration by 2-3 times, sensitivity disorders, neuritis, paralysis, etc. occur.

With hypovitaminosis B1, the pentose phosphate pathway of carbohydrate metabolism is also disturbed, in particular, the formation riboses.

hyperglycemia

hyperglycemia is an increase in blood sugar levels above normal. Depending on the etiological factors, the following types of hyperglycemia are distinguished:

Alimentary hyperglycemia. It develops when large amounts of sugar are taken. This type of hyperglycemia is used to assess the state of carbohydrate metabolism (the so-called sugar load). In a healthy person, after a single intake of 100-150 g of sugar, the blood glucose increases, reaching a maximum of 1.5-1.7 g / l (150-170 mg%) after 30-45 minutes. Then the blood sugar level begins to fall and after 2 hours it drops to normal (0.8-1.2 g / l), and after 3 hours it even turns out to be slightly reduced.

Emotional hyperglycemia. With a sharp predominance of the excitatory process over the inhibitory process in the cerebral cortex, excitation radiates to the underlying parts of the central nervous system. The flow of impulses along the sympathetic pathways, heading to the liver, enhances the breakdown of glycogen in it and inhibits the transition of carbohydrates into fat. At the same time, excitation acts through the hypothalamic centers and the sympathetic nervous system on the adrenal glands. There is a release into the blood of large amounts of adrenaline, which stimulates glycogenolysis.

Hormonal hyperglycemia. Occur in violation of the function of the endocrine glands, the hormones of which are involved in the regulation of carbohydrate metabolism. For example, hyperglycemia develops with an increase in the production of glucagon, a hormone of the α-cells of the islets of Langerhans of the pancreas, which, by activating liver phosphorylase, promotes glycogenolysis. Adrenaline has a similar effect. An excess of glucocorticoids (stimulates gluconeogenesis and inhibits hexokinase) and pituitary growth hormone (inhibits glycogen synthesis, promotes the formation of a hexokinase inhibitor and activates liver insulinase) leads to hyperglycemia.

Hyperglycemia with certain types of anesthesia. With ether and morphine anesthesia, sympathetic centers are excited and adrenaline is released from the adrenal glands; with chloroform anesthesia, this is accompanied by a violation of the glycogen-forming function of the liver.

Hyperglycemia due to insulin deficiency is the most persistent and pronounced. It is reproduced in the experiment by removing the pancreas. However, insulin deficiency is combined with severe indigestion. Therefore, a more perfect experimental model of insulin deficiency is deficiency caused by the introduction of alloxan (C4H2N2O4), which blocks SH-groups. In the β-cells of the islets of Langerhans of the pancreas, where the reserves of SH-groups are small, their deficiency quickly sets in and insulin becomes inactive.

Experimental insulin deficiency can be caused by dithizone, which blocks zinc in β-cells of the islets of Langerhans, which leads to a violation of the formation of granules from insulin molecules and its deposition. In addition, zinc dithizonate is formed in β-cells, which damages insulin molecules.

Insulin deficiency can be pancreatic or extrapancreatic. Both of these types of insulin deficiency can cause diabetes.

pancreatic insulin deficiency

This type of deficiency develops when pancreas:

tumors;

tuberculous / syphilitic process;

pancreatitis.

In these cases, all functions of the pancreas are disrupted, including the ability to produce insulin. After pancreatitis, insulin deficiency develops in 16-18% of cases due to excessive growth of connective tissue, which disrupts the supply of oxygen to cells.

Local hypoxia of the islets of Langerhans (atherosclerosis, vasospasm) leads to insulin deficiency, where blood circulation is normally very intense. At the same time, the disulfide groups in insulin are converted into sulfhydryl groups and it does not have a hypoglycemic effect). It is assumed that the cause of insulin deficiency can be the formation of alloxan in the body in violation of purine metabolism, which is similar in structure to uric acid.

The insular apparatus can be depleted after a preliminary increase in function, for example, when eating excessively digestible carbohydrates that cause hyperglycemia, when overeating. In the development of pancreatic insulin deficiency, an important role belongs to the initial hereditary inferiority of the insular apparatus.

Extrapancreatic insulin deficiency

This type of deficiency can develop with increased activity insulinase: an enzyme that breaks down insulin and is formed in the liver by the onset of puberty.

Insulin deficiency can be caused by chronic inflammatory processes, in which many proteolytic enzymes enter the bloodstream, destroying insulin.

Excess hydrocortisone, which inhibits hexokinase, reduces the effect insulin. Insulin activity decreases with an excess of non-esterified fatty acids in the blood, which have a direct inhibitory effect on it.

The cause of insulin deficiency may be its excessively strong connection with the carrying proteins in the blood. Protein-bound insulin is not active in the liver and muscles, but usually has an effect on adipose tissue.

In some cases, with diabetes mellitus, the level of insulin in the blood is normal or even elevated. It is assumed that diabetes is due to the presence of an insulin antagonist in the blood, but the nature of this antagonist has not been established. The formation of antibodies against insulin in the body leads to the destruction of this hormone.

Diabetes

carbohydrate metabolism in diabetes mellitus is characterized by the following features:

The synthesis of glucokinase is sharply reduced, which almost completely disappears from the liver in diabetes, which leads to a decrease in the formation of glucose-6-phosphate in the liver cells. This moment, along with reduced synthesis of glycogen synthetase, causes a sharp slowdown in glycogen synthesis. The liver becomes depleted of glycogen. With a lack of glucose-6-phosphate, the pentose phosphate cycle is inhibited;

The activity of glucose-6-phosphatase increases sharply, so glucose-6-phosphate is dephosphorylated and enters the blood in the form of glucose;

The transition of glucose into fat is inhibited;

The passage of glucose through cell membranes decreases, it is poorly absorbed by tissues;

Gluconeogenesis is sharply accelerated - the formation of glucose from lactate, pyruvate, amino acids, fatty acids and other products of non-carbohydrate metabolism. Acceleration of gluconeogenesis in diabetes mellitus is due to the absence of an inhibitory effect (suppression) of insulin on enzymes that provide gluconeogenesis in liver and kidney cells: pyruvate carboxylase, glucose-6-phosphatase.

Thus, in diabetes mellitus, there is an excess production and insufficient use of glucose by tissues, resulting in hyperglycemia. The content of sugar in the blood in severe forms can reach 4-5 g / l (400-500 mg%) and above. At the same time, the osmotic pressure of the blood increases sharply, which leads to dehydration of the cells of the body. In connection with dehydration, the functions of the central nervous system are deeply disturbed (hyperosmolar coma).

The sugar curve in diabetes compared to that in healthy people is significantly extended over time. The significance of hyperglycemia in the pathogenesis of the disease is twofold. It plays an adaptive role, since it inhibits the breakdown of glycogen and partially enhances its synthesis. With hyperglycemia, glucose penetrates better into tissues and they do not experience a sharp lack of carbohydrates. Hyperglycemia also has negative implications.

With it, the concentration of gluco- and mucoproteins increases, which easily fall out in the connective tissue, contributing to the formation of hyaline. Therefore, early vascular damage by atherosclerosis is characteristic of diabetes mellitus. The atherosclerotic process captures the coronary vessels of the heart (coronary insufficiency), the vessels of the kidneys (glomerulonephritis). In the elderly, diabetes mellitus can be combined with hypertension.

Glucosuria

Normally, glucose is found in provisional urine. In the tubules, it is reabsorbed in the form of glucose phosphate, for the formation of which hexokinase is required, and after dephosphorylation enters the blood. Thus, the final urine does not contain sugar under normal conditions.

In diabetes, the processes of phosphorylation and dephosphorylation of glucose in the tubules of the kidneys cannot cope with excess glucose in the primary urine. Developing glycosuria. In severe forms of diabetes, the sugar content in the urine can reach 8-10%. The osmotic pressure of urine is increased; in this regard, a lot of water passes into the final urine.

Daily diuresis increases to 5-10 liters or more (polyuria). Dehydration of the body develops, increased thirst (polydipsia) develops. In case of violation of carbohydrate metabolism, you should contact endocrinologist for professional help. The doctor will select the necessary medication and develop an individual diet.

Not the last role is played by carbohydrates. People who care about their own health know that complex carbohydrates are preferable to simple ones. And that it is better to eat food for longer digestion and energizing throughout the day. But why exactly? What is the difference between the processes of assimilation of slow and fast carbohydrates? Why sweets should be used only to close the protein window, and honey is better to eat only at night? To answer these questions, let's take a closer look at the metabolism of carbohydrates in the human body.

What are carbohydrates for?

In addition to maintaining optimal weight, carbohydrates in the human body perform a huge amount of work, a failure in which leads not only to obesity, but also to a host of other problems.

The main tasks of carbohydrates are to perform the following functions:

Energy - Approximately 70% of calories come from carbohydrates. In order to realize the process of oxidation of 1 g of carbohydrates, the body needs 4.1 kcal of energy.
Construction - take part in the construction of cellular components.
Reserve - create a depot in the muscles and liver in the form of glycogen.
Regulatory - Some hormones are glycoproteins in nature. For example, thyroid and pituitary hormones - one structural part of such substances is protein, and the other is carbohydrate.
Protective - heteropolysaccharides are involved in the synthesis of mucus, which covers the mucous membranes of the respiratory tract, digestive organs, and the genitourinary tract.
They are involved in cell recognition.
They are part of the membranes of erythrocytes.
They are one of the regulators of blood clotting, as they are part of prothrombin and fibrinogen, heparin (- textbook "Biological Chemistry", Severin).

For us, the main sources of carbohydrates are those molecules that we get from food: starch, sucrose and lactose.

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Steps in the breakdown of saccharides

Before considering the features of biochemical reactions in the body and the effect of carbohydrate metabolism on athletic performance, let's study the process of splitting saccharides with their further transformation into the very one that athletes so desperately get and spend while preparing for competitions.

Stage 1 - pre-digestion with saliva

Unlike proteins and fats, carbohydrates begin to break down almost immediately after they enter the mouth. The fact is that most of the products that enter the body contain complex starchy carbohydrates, which, under the influence of saliva, namely the amylase enzyme, which is part of it, and the mechanical factor, are broken down into simple saccharides.

Stage 2 - influence of stomach acid on further digestion

This is where stomach acid comes into play. It breaks down complex saccharides that have not been exposed to saliva. In particular, under the action of enzymes, lactose is broken down to galactose, which subsequently turns into glucose.

Stage 3 - absorption of glucose into the blood

At this stage, almost all fermented fast glucose is directly absorbed into the blood, bypassing the fermentation processes in the liver. The energy level rises sharply, and the blood becomes more saturated.

Stage 4 - satiety and insulin response

Under the influence of glucose, the blood thickens, which makes it difficult to move and transport oxygen. Glucose replaces oxygen, which causes a protective reaction - a decrease in the amount of carbohydrates in the blood.

The plasma receives insulin and glucagon from the pancreas.

The first opens the transport cells to move sugar into them, which restores the lost balance of substances. Glucagon, in turn, reduces the synthesis of glucose from glycogen (the consumption of internal energy sources), and insulin "holes" the main cells of the body and puts glucose there in the form of glycogen or lipids.

Stage 5 - carbohydrate metabolism in the liver

On the way to complete digestion, carbohydrates collide with the body's main defender - liver cells. It is in these cells that carbohydrates, under the influence of special acids, bind into the simplest chains - glycogen.

Stage 6 - glycogen or fat

The liver can process only a certain amount of monosaccharides in the blood. Rising insulin levels make her do it in no time. If the liver does not have time to convert glucose into glycogen, a lipid reaction occurs: all free glucose, by binding with acids, is converted into simple fats. The body does this in order to leave a reserve, however, in view of our constant nutrition, it “forgets” to digest, and the glucose chains, turning into plastic fatty tissues, are transported under the skin.

Stage 7 - secondary splitting

In the event that the liver coped with the sugar load and was able to convert all carbohydrates into glycogen, the latter, under the influence of the hormone insulin, has time to stock up in the muscles. Further, under conditions of lack of oxygen, it is broken down back to the simplest glucose, not returning to the general bloodstream, but remaining in the muscles. Thus, bypassing the liver, glycogen supplies energy for specific muscle contractions, while increasing endurance (- "Wikipedia").

This process is often referred to as "second wind". When an athlete has large stores of glycogen and simple visceral fats, they will turn into clean energy only in the absence of oxygen. In turn, alcohols contained in fatty acids will stimulate additional vasodilation, which will lead to better cell susceptibility to oxygen in conditions of its deficiency.

Features of metabolism according to GI

It is important to understand why carbohydrates are divided into simple and complex. It's all about them, which determines the rate of decay. This, in turn, triggers the regulation of carbohydrate metabolism. The simpler the carbohydrate, the faster it gets to the liver and the more likely it is to be converted into fat.

An approximate table of the glycemic index with the total composition of carbohydrates in the product:

Features of metabolism according to GN

However, even foods with a high glycemic index are not able to disrupt the metabolism and functions of carbohydrates in the way that it does. It determines how strongly the liver will be loaded with glucose when using this product. When a certain GL threshold is reached (about 80-100), all calories in excess of the norm will be automatically converted into triglycerides.

Approximate table of glycemic load with total calories:

Insulin and glucagon response

In the process of consuming any carbohydrate, be it sugar or complex starch, the body starts two reactions at once, the intensity of which will depend on the previously discussed factors and, first of all, on the release of insulin.

It is important to understand that insulin is always released into the blood in pulses. And this means that one sweet pie is as dangerous for the body as 5 sweet patties. Insulin regulates the thickness of the blood. This is necessary so that all cells get enough energy without working in hyper- or hypo-mode. But most importantly, the speed of its movement, the load on the heart muscle and the ability to transport oxygen depend on the density of the blood.

The release of insulin is a natural response. Insulin perforates all the cells in the body that are capable of receiving additional energy, and locks it in them. If the liver has coped with the load, glycogen is placed in the cells, if the liver has not coped, then fatty acids enter the same cells.

Thus, the regulation of carbohydrate metabolism occurs solely due to the release of insulin. If it is not enough (not chronically, but one-time), a person may experience a sugar hangover - a condition in which the body requires additional fluid to increase blood volume, and dilute it by all available means.
Subsequent energy distribution
The subsequent distribution of carbohydrate energy occurs depending on the type of addition, and the fitness of the body:
In an untrained person with a slow metabolism. Glycogen cells with a decrease in glucagon levels return to the liver, where they are processed into triglycerides.
At the athlete. Glycogen cells under the influence of insulin are massively locked in the muscles, providing an energy reserve for the following exercises.
In a non-athlete with a fast metabolism. Glycogen returns to the liver, being transported back to the level of glucose, after which it saturates the blood to the borderline level. By this, it provokes a state of exhaustion, because despite sufficient nutrition with energy resources, the cells do not have the appropriate amount of oxygen.

Outcome
Energy metabolism is a process in which carbohydrates are involved. It is important to understand that even in the absence of direct sugars, the body will still break down tissues to the simplest glucose, which will lead to a decrease in muscle tissue or body fat (depending on the type of stressful situation).

The metabolic processes of carbohydrates in the human body play an important role. In addition, they perform many functions, the main of which remains energy.

Many people know that carbohydrates are organic compounds that are the main source of energy. However, is it only in the supply of energy that the main role of carbohydrates in the human body lies? Undeniably not. In the human body, all processes not only matter, but they are almost always interconnected. So, carbohydrates, which are found in all tissues, can exist freely or in the form of associations with proteins and fats. Therefore, if the metabolism of carbohydrates is disturbed, then this will invariably lead to failures in other metabolisms. But what else are carbohydrates for, what is their significance and function?

The meaning and function of carbohydrates

Carbohydrates are the predominant part of the human diet. They support, in fact, all the life support of the body, provide more than 50% of the daily energy value of food, and that is why they are delivered 2 times more than other substances. It should be noted that as the load on the muscles increases, the amount of carbohydrates consumed also increases.

Nevertheless, they are needed not only as replenishers of energy costs. Along with proteins and fats, they are the “building material” for cells, because of their presence, the production of amino acids and nucleic acids becomes possible, and they also provide the right amount of glycogen and glucose. So their value is great.

It is important to know that carbohydrates are an integral part of all living organisms, causing the specifics of their construction. They include associations that have different and sometimes significantly different functions. If we talk about the functions of the carbohydrates themselves, then they boil down to the following:

the main source of energy;
controls the metabolism of proteins and lipids;
ensures the work of the brain;
perform the functions of producing ATP, DNA and RNA molecules;
together with proteins carry out the synthesis of certain hormones, enzymes, secrets;
insoluble carbohydrate fibers help improve the functioning of the digestive tract;
fiber also removes toxic substances, and pectin activates digestion.

Although carbohydrates can hardly be called indispensable, nevertheless, their deficiency leads to a decrease in the glycogen reserve in the liver and to fatty deposits in its cells. Such processes not only affect the functioning of the liver, but can also cause its fatty degeneration.

But these are far from all the pathologies that are observed with a lack of carbohydrates. So they are indispensable elements of the diet, since they not only provide the energy costs of the body, but also take part in cellular metabolism.

Types of carbohydrates

Various typologies of carbohydrates and their structural components are used. A considerable number of people divide them into 2 main subgroups - simple and complex. However, according to their chemical constituents, they form 3 subgroups:

monosaccharides;
oligosaccharides;
polysaccharides.

Monosaccharides can have one sugar molecule or they can have two (disaccharides). They include glucose, fructose, sucrose and other substances. By and large, they do not break down, and enter the bloodstream unchanged, which leads to spikes in sugar levels. Oligosaccharides are carbohydrates, which are characterized by transformation by hydrolysis into a small number of monosaccharides (from 3 to 10).

Polysaccharides are made up of many monosaccharides. These include starches, dextrins and fiber. Their transformation in the gastrointestinal tract takes a long time, which allows you to achieve a stable blood sugar level without the insulin spikes that ordinary monosaccharides cause.

Although their breakdown occurs in the digestive tract, however, its transformation begins in the mouth. Saliva causes their partial conversion into maltose and that is why it is so important to chew food thoroughly.

carbohydrate metabolism

Of course, the leading role of carbohydrates is to provide an energy reserve. Glucose in the blood is the main source of energy. The speed of its splitting, oxidation and the probability of ultra-fast withdrawal from the depot guarantee the instant use of reserves in case of physical and mental overload.

Carbohydrate metabolism is that combination of processes that makes it possible for the conversion of carbohydrates in the human body. Carbohydrate conversion starts in the mouth, where starch is broken down by the enzyme amylase. The main carbohydrate metabolism occurs already in the intestine, where one can observe the transformation of polysaccharides into monosaccharides, which are delivered to the tissues with blood. But their lion's share is concentrated in the liver (glycogen).

Together with the blood, glucose is sent to those organs that need these receipts the most. Nevertheless, the rate of glucose delivery to cells is directly proportional to the permeability of cell membranes.

So, it enters the liver cells easily, and into the muscles only with additional energy consumption. But the permeability of the membranes increases when the muscles work.

Glucose, while in cells, can be converted both anaerobically (without oxygen) and aerobically (with oxygen). In the first case, that is, during glycolysis, glucose is broken down into adenosine triphosphate and lactic acid. In the pentose cycle, the final products of its decomposition will be carbon dioxide, water and an energy reserve in the form of ATP.

It is important to remember that the metabolic processes of all the main nutrients are connected, so their interconversions are likely within certain limits. The exchange of carbohydrates, proteins and lipids at a certain point involves the formation of intermediate substances that are common for all metabolic processes (acetyl coenzyme A). With its help, the exchange of all important nutrients leads to a cycle of tricarboxylic acids, which contributes to the release of up to 70% of energy.

Deficiency and excess of carbohydrates

As already mentioned, the lack of carbohydrates leads to liver degeneration. But that's not all. With a lack of carbohydrates, not only fats are split, muscles also suffer. In addition, ketones begin to accumulate in the blood, whose high concentration can oxidize the internal environment of the body and cause intoxication of brain tissues.

Excess carbohydrates are also detrimental. In the initial stage, it causes an increase in blood sugar, which overloads the pancreas. Regular abuse of simple carbohydrates depletes it, which can lead to the development of both types of diabetes.

But even if this does not happen, what part of the carbohydrates will still not be processed, but will turn into fat. And obesity is already pulling with it other ailments, for example, atherosclerosis and related cardiovascular diseases. That is why it is so important to know the measure in everything, because health directly depends on it.

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

The average daily carbohydrate requirement for an adult is 400-450 g.

The main stages of carbohydrate metabolism are:

1) the breakdown of food carbohydrates in the gastrointestinal tract and the absorption of monosaccharides in the small intestine;

2) 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 in the blood (mobilization of glycogen);

4) synthesis of glucose from intermediate products (pyruvic and lactic acids) and non-carbohydrate precursors;

5) 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 (a polysaccharide). The process of glycogen synthesis in the liver from glucose is called glycogenesis (the liver contains about 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, etc.).

Glucose is a constant component (biological constant) of blood. The content of glucose in human blood is normally 4.44-6.67 mmol / l (80-120 mg%). With an increase in its content in the blood (hyperglycemia) to 8.34-10 mmol / l (150-180 mg%), it is excreted in the urine in the form of traces. With a decrease in blood glucose (hypoglycemia) to 3.89 mmol / l (70 mg%), a feeling of hunger appears, to 3.22 mmol / l (40 mg%) - 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 process by which glycogen is broken down into glucose in the liver is called glycogenolysis. The process of biosynthesis of carbohydrates from their breakdown products or breakdown products of fats and proteins is called glyconeogenesis. The process of carbohydrate breakdown in the absence of oxygen with the accumulation of energy in ATP and the formation of lactic and pyruvic acids is called glycolysis.

When the intake of glucose exceeds the immediate need for this substance, 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 primarily 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 this 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. We will consider this pathology in more detail when studying the endocrine system.

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 their chemical structure, carbohydrates 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 - monosaccharide with 3 carbon atoms
tetrose - a monosaccharide with 4 carbon atoms
pentose - a monosaccharide with 5 carbon atoms
hexose - monosaccharide with 6 carbon atoms
heptose - monosaccharide with 7 carbon atoms

The hexose group includes glucose, galactose and fructose.

Glucose, 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 converted into glucose sooner or later in the liver.

Oligosaccharides

Oligosaccharides are composed of 2-10 monosaccharides linked together. 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:

Starch is a vegetable storage form of carbohydrates. Starch exists in two forms: amylose or aminopectin. Amylose is a long, unbranched chain of helically twisted glucose molecules, while amylopectin is a highly branched group of linked monosaccharides.
Dietary fiber 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 what follows.

Digested glucose

Assimilated, glucose is the main source of energy (during or immediately after a meal). This glucose is catabolized by cells to provide energy for the formation of ATP. 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 source of fuel. 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 conclusions

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.