Protein and carbohydrate metabolism. Features of the metabolism of fats, proteins and carbohydrates depending on the types of nutrition

Entering the body, food molecules are involved in many reactions. These reactions and other manifestations of vital activity are metabolism (metabolism). Nutrients are used as raw materials for the synthesis of new cells, oxidized, delivering energy. Part of it is used for the synthesis of new cells, the other part is used for the functioning of these cells. the remaining energy is released as heat. Exchange processes:

Anabolism (assimilation) - chemical process, at which simple substances are combined with each other into complex ones. This leads to energy storage and growth. Catabolism - dissimilation - the splitting of complex substances into simple ones with the release of energy. The essence of metabolism is the intake of substances into the body, their assimilation, use and excretion of metabolic products. Metabolic functions:

extraction of energy from the external environment in the form of chemical energy of organic substances

turning these substances into building blocks

assembly of cellular components from these blocks

synthesis and destruction of biomolecules that are necessary for the performance of functions

Protein metabolism is a set of processes of protein transformation in the body, including the exchange of amino acids. Proteins are the basis of all cell structures, material carriers of life, the main building material. Daily requirement - 100 - 120g. Proteins are made up of amino acids (23):

interchangeable - can be formed from others in the body

Essential - cannot be synthesized in the body and must

come with food - valine, leucine, isoleucine, lysine, arginine, tryptophan, histidine Stages of protein metabolism:

1. enzymatic breakdown of food proteins to amino acids

2. absorption of amino acids into the blood

3. conversion of amino acids into intrinsic given organism

4. biosynthesis of proteins from these acids

5. breakdown and use of proteins

6. the formation of amino acid cleavage products blood capillaries small intestine, amino acids on the portal

veins enter the liver, where they are used or retained. Part of the amino acids remains in the blood, enters the cells, where new proteins are built from them.

The protein renewal period in humans is 80 days. If a large amount of protein is supplied with food, then liver enzymes split off amino groups (NH2) from them - deamination. Other enzymes combine amino groups with CO2, and urea is formed, which enters the kidneys with the blood and is normally excreted in the urine. Proteins are almost not deposited in the depot, therefore, after the depletion of carbohydrate and fat reserves, not reserve proteins are used, but cell proteins. This condition is very dangerous - protein starvation - the brain and other organs suffer (protein-free diets). There are proteins of animal and vegetable origin. Animal proteins - meat, fish and seafood, vegetable - soy, beans, peas, lentils, mushrooms, which are necessary for normal protein metabolism.

Fat metabolism - a set of processes of transformation of fats in the body. Fats are an energetic and plastic material; they are part of the membranes and cytoplasm of cells. Part of the fat accumulates in the form of reserves in the subcutaneous adipose tissue, greater and lesser omentums and around some internal organs (kidneys) - 30% of the total body weight. The main mass of fats is neutral fat, which is involved in fat metabolism. The daily requirement for fats is 100 gr.

Some fatty acids are indispensable for the body and must be supplied with food - these are polyunsaturated fatty acids: linolenic, linoleic, arachidonic, gamma-aminobutyric (seafood, dairy products). Gamma-aminobutyric acid is the main inhibitory substance in the central nervous system. Thanks to her, there is a regular change in the phases of sleep and wakefulness, right job neurons. Fats are divided into animal and vegetable (oils), which are very important for normal fat metabolism.

Stages of fat metabolism:

1. enzymatic breakdown of fats in the gastrointestinal tract to glycerol and fatty acids

2. formation of lipoproteins in the intestinal mucosa

3. transport of lipoproteins by blood

4. hydrolysis of these compounds on the surface of cell membranes

5. absorption of glycerol and fatty acids into cells

6. synthesis of own lipids from fat breakdown products

7. oxidation of fats with the release of energy, CO2 and water

With excessive intake of fats with food, it goes into glycogen in the liver or is deposited in the reserve. With food rich in fats, a person receives fat-like substances - phosphatides and stearins. Phosphatides are essential for building cell membranes, nuclei and

cytoplasm. They are rich nervous tissue. Cholesterol is the main representative of stearins. Its norm in plasma is 3.11 - 6.47 mmol / l. The yolk is rich in cholesterol chicken egg, butter, liver. It is necessary for the normal functioning of the nervous system, the reproductive system, cell membranes, sex hormones. In pathology, it leads to atherosclerosis.

Carbohydrate metabolism is the totality of the transformation of carbohydrates in the body. Carbohydrates are a source of energy in the body for direct use (glucose) or depot formation (glycogen). Daily requirement - 500 gr.

Stages of carbohydrate metabolism:

1. enzymatic breakdown of food carbohydrates to monosaccharides

2. absorption of monosaccharides in small intestine

3. deposition of glucose in the liver in the form of glycogen or its direct use

4. breakdown of glycogen in the liver and the entry of glucose into the blood

5. oxidation of glucose with the release of CO2 and water

Carbohydrates are absorbed in the gastrointestinal tract in the form of glucose, fructose and galactose, enter the blood

- in the liver portal vein- Glucose is converted to glycogen. The process of converting glucose to glycogen in the liver is called glycogenesis. Glucose is a constant component of the blood (80 - 120 mlg/%). An increase in blood glucose is hyperglycemia, a decrease is hypoglycemia. A decrease in glucose levels to 70 mlg /% causes a feeling of hunger, to 40 mlg /% - to coma.

The process of breakdown of glycogen in the liver to glucose is called glycogenolysis. The process of biosynthesis of carbohydrates from the breakdown products of fats and proteins is gluconeogenesis. The process of splitting carbohydrates without oxygen with the accumulation of energy and the formation of lactic and pyruvic acids is glycolysis. When glucose in food increases, the liver converts it into fat, which is then used.

The liver, being the central organ of metabolism, is involved in maintaining metabolic homeostasis and is able to interact with the reactions of protein, fat and carbohydrate metabolism.

The places of "connection" of the metabolism of carbohydrates and proteins are pyruvic acid, oxaloacetic and α-ketoglutaric acids from TCA, capable of being converted in transamination reactions, respectively, into alanine, aspartate and glutamate. The process of converting amino acids into keto acids proceeds similarly.

Carbohydrates are even more closely related to lipid metabolism:

NADPH molecules formed in the pentose phosphate pathway are used for the synthesis of fatty acids and cholesterol,
glyceraldehyde phosphate, also formed in the pentose phosphate pathway, is included in glycolysis and converted to dihydroxyacetone phosphate,
glycerol-3-phosphate, formed from glycolysis dihydroxyacetone phosphate, is sent for the synthesis of triacylglycerols. Also for this purpose, glyceraldehyde-3-phosphate, synthesized in the stage of structural rearrangements of the pentose phosphate pathway, can be used,
"glucose" and "amino acid" acetyl-SCoA is able to participate in the synthesis of fatty acids and cholesterol.

carbohydrate metabolism

Carbohydrate metabolism processes are actively taking place in hepatocytes. Through the synthesis and breakdown of glycogen, the liver maintains the concentration of glucose in the blood. Active glycogen synthesis occurs after a meal, when the concentration of glucose in the blood of the portal vein reaches 20 mmol / l. Glycogen stores in the liver range from 30 to 100 g. intermittent fasting going on glycogenolysis, when prolonged fasting main source of blood glucose is gluconeogenesis from amino acids and glycerol.

Liver carries out sugar interconversion, i.e. conversion of hexoses (fructose, galactose) into glucose.

Active reactions of the pentose phosphate pathway provide the production of NADPH required for microsomal oxidation and synthesis of fatty acids and cholesterol from glucose.

lipid metabolism

If, during a meal, an excess of glucose enters the liver, which is not used for the synthesis of glycogen and other syntheses, then it turns into lipids - cholesterol and triacylglycerols. Since the liver cannot store TAGs, their removal occurs with the help of very low density lipoproteins ( VLDL). Cholesterol is used primarily for the synthesis bile acids, it is also included in the composition of low density lipoproteins ( LDL) and VLDL.

Under certain conditions - fasting, prolonged muscle load, type I diabetes, fat rich diet - synthesis is activated in the liver ketone bodies used by most fabrics as alternative source energy.

Protein metabolism

More than half of the protein synthesized per day in the body comes from the liver. The rate of renewal of all liver proteins is 7 days, while in other organs this value corresponds to 17 days or more. These include not only the proteins of the hepatocytes themselves, but also those going for "export" - albumins, many globulins, blood enzymes, as well as fibrinogen and clotting factors blood.

Amino acids undergo catabolic reactions with transamination and deamination, decarboxylation with the formation of biogenic amines. Synthetic reactions take place choline and creatine due to the transfer of the methyl group from adenosylmethionine. In the liver, excess nitrogen is utilized and included in the composition urea.

Reactions for the synthesis of urea are closely related to the tricarboxylic acid cycle.

Close interaction between urea synthesis and TCA

pigment exchange

The participation of the liver in pigment metabolism consists in the conversion of hydrophobic bilirubin into a hydrophilic form and its secretion into bile.

Pigment metabolism, in turn, plays an important role in iron metabolism in the body - ferritin is an iron-containing protein in hepatocytes.

Assessment of metabolic function

AT clinical practice There are methods for evaluating a particular function:

Participation in carbohydrate metabolism is assessed:

on glucose concentration blood,
according to the steepness of the tolerance test curve glucose,
on the "sugar" curve after the load galactose,
according to the magnitude of hyperglycemia after administration hormones(for example, adrenaline).

The role in lipid metabolism is considered:

by blood level triacylglycerols, cholesterol, VLDL, LDL, HDL,
by coefficient atherogenicity.

Protein metabolism is estimated:

by concentration total protein and its fractions in blood serum,
by indicators coagulograms,
by level urea in blood and urine
by activity enzymes AST and ALT, LDH-4.5, alkaline phosphatase, glutamate dehydrogenase.

Pigment exchange is assessed:

by concentration of total and direct bilirubin in blood serum.

Ministry of Education and Science of the Russian Federation

federal state budgetary educational institution higher professional education

Perm National Research Polytechnic University

Department of Environmental Protection

Course work in the discipline "Physiology"

Protein metabolism. Fat metabolism. The exchange of carbohydrates. Liver, its role in metabolism.

Completed by: student of the OOS-11 group

Myakisheva Alexandra

Introduction

Chapter 1

1.1 Proteins and their functions

1.2 Intermediate protein metabolism

1.3 Regulation of protein metabolism

1.4 Balance of nitrogen metabolism

Chapter 2

2.1 Fats and their functions

2.2 Digestion and absorption of fats in the body

2.3 Regulation of fat metabolism

Chapter 3

3.1 Carbohydrates and their functions

3.2 Breakdown of carbohydrates in the body

3.3 Regulation of carbohydrate metabolism

Chapter 4

4.1 Structure of the liver

4.2 Functions of the liver

4.3 The role of the liver in metabolism

Conclusion

Bibliography

Introduction

Normal activity of the body is possible with a continuous supply of food. Fats, proteins, carbohydrates in food mineral salts, water and vitamins are necessary for the life processes of the body.

Nutrients are proteins, fats and carbohydrates. These substances are both a source of energy that covers the expenses of the body, and a building material that is used in the process of growth of the body and the reproduction of new cells that replace the dying ones. But nutrients in the form in which they are eaten cannot be absorbed and used by the body. Only water, mineral salts and vitamins are absorbed and assimilated in the form in which they come. In the digestive tract, proteins, fats and carbohydrates are subjected to physical influences (crushed and ground) and chemical changes that occur under the influence of special substances - enzymes contained in the juices of the digestive glands. Under the influence of digestive juices, nutrients are broken down into simpler ones, which are absorbed and absorbed by the body. In turn, the liver is a regulator of the content in the blood of substances entering the body as part of food products. It maintains the stability of the internal environment of the body. In the liver flow critical processes carbohydrate, protein and fat metabolism.

The purpose of the work: To assess the metabolism of fats, proteins and carbohydrates. Determine the role of the liver in metabolism.

.Learn how proteins, fats and carbohydrates are exchanged

.Get to know specific properties proteins, fats and carbohydrates

.Analyze the role of the liver in metabolism

fat protein carbohydrate liver

Chapter 1

Life is a form of existence of protein bodies (F. Engels).

The exchange of proteins in the human body plays a primary role in their destruction and restoration. In a healthy person, under normal conditions, 1-2% of the total amount of body proteins is updated per day, which is mainly due to splitting (degradation) muscle proteins to the level of free amino acids. About 80% of the released amino acids are reused in the processes of protein biosynthesis, the rest takes part in various reactions metabolism<#"justify">1.1 Proteins and their functions

Protein - high-molecular organic substances, consisting of alpha-amino acids connected in a chain by a peptide bond.

Proteins are the main substance from which the protoplasm of cells and intercellular substances are built. Without proteins there is no and cannot be life. All the enzymes without which they cannot proceed metabolic processes, are protein bodies.

The structure of proteins is very complex. When hydrolyzed by acids, alkalis and proteolytic enzymes, the protein is broken down into amino acids, total number more than twenty five. In addition to amino acids, various proteins also contain many other components (phosphoric acid, carbohydrate groups, lipoid groups, special groups).

Proteins are highly specific. In every organism and in every tissue there are proteins that are different from the proteins that make up other organisms and other tissues. The high specificity of proteins can be detected using a biological sample.

The main significance of proteins lies in the fact that cells and intercellular substance are built at their expense and substances that are involved in the regulation of physiological functions are synthesized. To a certain extent, proteins, however, along with carbohydrates and fats, are also used to cover energy costs.

Protein Functions:

· The plastic function of proteins is to ensure the growth and development of the body through the processes of biosynthesis. Proteins are part of all body cells and interstitial structures.

· Enzymatic activity proteins regulate the rate of biochemical reactions. Enzyme proteins determine all aspects of metabolism and the formation of energy not only from the proteins themselves, but from carbohydrates and fats.

· Protective function proteins consists in the formation of immune proteins - antibodies. Proteins are able to bind toxins and poisons and also ensure blood clotting (hemostasis).

· The transport function consists in the transfer of oxygen and carbon dioxide by the erythrocyte protein hemoglobin, as well as in the binding and transfer of certain ions (iron, copper, hydrogen), medicinal substances, toxins.

· The energy role of proteins is due to their ability to release energy during oxidation. However, the plastic role of proteins in metabolism exceeds their energetic and plastic role of other nutrients. The need for protein is especially great during periods of growth, pregnancy, recovery after serious illnesses.

In the digestive tract, proteins are broken down to amino acids and the simplest polypeptides, from which later the cells of various tissues and organs, in particular the liver, synthesize proteins specific to them. Synthesized proteins are used to restore destroyed and grow new cells, the synthesis of enzymes and hormones.

1.2 Intermediate protein metabolism

The breakdown (cleavage) of proteins in the body mainly occurs due to enzymatic hydrolysis. The main material for the renewal of cellular proteins are amino acids obtained during the processing of food that contains proteins. The absorption of amino acids into the blood occurs mainly in the small intestine, where certain amino acid transport systems exist. With the help of the bloodstream, amino acids are delivered to all organs and tissues of the human body. The maximum concentration of amino acids is reached 30-50 minutes after ingestion of protein foods. By changing the quantitative ratio between amino acids entering the body or excluding one or another amino acid from the diet, it is possible to judge the importance of individual amino acids for the body by the state of nitrogen balance, height, body weight and general condition of animals. It has been experimentally established that of the 20 amino acids that make up proteins, 12 are synthesized in the body - non-essential amino acids, and 8 are not synthesized - essential amino acids.

Without essential amino acids, protein synthesis is drastically disrupted and a negative nitrogen balance sets in, growth stops, and body weight decreases. For people essential amino acids are leucine, isoleucine, valine, methionine, lysine, threonine, phenylalanine, tryptophan.

Proteins are not deposited in the body; are not kept in stock. Most of the proteins that come with food are used for energy purposes. For plastic purposes - i.e. only a small part of it is spent on the formation of new tissues (organs, muscles). Therefore, in order to add body weight due to protein, its intake into the body in increased quantities is necessary.

The rate of protein renewal is not the same for different tissues. Proteins of the liver, intestinal mucosa, and blood plasma are updated with the greatest speed. The proteins that make up the cells of the brain, heart, and sex glands are slowly updated. The proteins of the skin, muscles, especially the supporting tissues - tendons, cartilage and bones are renewed even more slowly.

1.3 Regulation of protein metabolism

Neuroendocrine regulation of protein metabolism is carried out by a number of hormones. The somatotropic hormone of the pituitary gland during the growth of the body stimulates an increase in the mass of all organs and tissues. In an adult, it provides the process of protein synthesis by increasing the permeability of cell membranes for amino acids, enhancing RNA synthesis in the cell nucleus and suppressing the synthesis of cathepsins - intracellular proteolytic enzymes. Significant impact on protein metabolism have hormones thyroid gland thyroxine and triiodothyronine. They can in certain concentrations stimulate protein synthesis and thereby activate the growth, development and differentiation of tissues and organs. With Graves' disease, characterized by increased secretion of thyroid hormones (hyperthyroidism), protein metabolism is increased. On the contrary, with hypofunction of the thyroid gland (hypothyroidism), the intensity of protein metabolism is sharply reduced. Since the activity of the thyroid gland is under control nervous system, then the latter is the true regulator of protein metabolism. Hormones of the adrenal cortex - glucocorticoids (hydrocortisone, corticosterone) increase the breakdown of proteins in tissues, especially in muscle and lymphoid. In the liver, glucocorticoids, on the contrary, stimulate protein synthesis.

The course of protein metabolism is greatly influenced by the nature of the food. With meat food, the amount of formed uric acid, creatinine and ammonia. With plant foods, these substances are formed in much smaller quantities, since there are few purine bodies and creatine in plant foods.

1.4 Balance of nitrogen metabolism

Creatinine and hippuric acid are also important end products of nitrogen metabolism. Creatinine is creatine anhydride. Creatine is found in the muscles and in the brain tissue in a free state and in combination with phosphoric acid (phosphocreatine). Hippuric acid is synthesized from benzoic acid and glycocol (in humans, mainly in the liver and, to a lesser extent, in the kidneys).

Protein breakdown products, sometimes with a large physiological significance, are amines (eg, histamine).

The study of protein metabolism is facilitated by the fact that nitrogen is included in the composition of the protein. The nitrogen content in various proteins ranges from 14 to 19%, on average it is 16%, i.e. 1 g of nitrogen is contained in 6.25 g of protein. Therefore, multiplying the found amount of nitrogen by 6.25, you can determine the amount of digested protein. There is a relationship between the amount of nitrogen introduced with food proteins and the amount of nitrogen excreted from the body. An increase in the intake of protein in the body leads to an increase in the excretion of nitrogen from the body. In an adult with adequate nutrition, as a rule, the amount of nitrogen introduced into the body is equal to the amount of nitrogen excreted from the body. This state is called nitrogen balance. If, under conditions of nitrogen balance, the amount of protein in food is increased, then the nitrogen balance will soon be restored, but already at a new, more high level. Thus, nitrogen balance can be established with significant fluctuations in the protein content of food.

During body growth or weight gain due to the assimilation of an increased amount of proteins (for example, after starvation, after infectious diseases), the amount of nitrogen introduced with food is greater than the amount excreted. Nitrogen is retained in the body in the form of protein nitrogen. This is referred to as a positive nitrogen balance. During starvation, in diseases accompanied by a large breakdown of proteins, there is an excess of excreted nitrogen over the input, which is referred to as a negative nitrogen balance. In this case, it does not full recovery squirrel. With a lack of protein in food, liver and muscle proteins are consumed.

In the body, proteins are not stored in reserve, but only temporarily retained in the liver. Normal life activity of the organism is possible with nitrogen balance or positive nitrogen balance.

When proteins enter the body in an amount less than this corresponds to the protein minimum, the body experiences protein starvation: the loss of proteins by the body is insufficiently replenished. For a more or less long period, depending on the degree of starvation, a negative protein balance does not threaten dangerous consequences. However, if the fasting does not stop, death ensues.

With prolonged general starvation, the amount of nitrogen excreted from the body decreases sharply for the first days, then sets at a constant low level. This is due to the exhaustion of the last remnants of other energy resources in particular fats.

Chapter 2

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

The use of fat as an energy source begins with its release from fat depots into the bloodstream. This process is called fat mobilization. Fat mobilization is accelerated by the action of the sympathetic nervous system and the hormone adrenaline.

1 Fats and their functions

Fats are natural organic compounds, full esters of glycerol and monobasic fatty acids; belong to the class of lipids.

In living organisms, they perform primarily structural and energy functions: they are the main component of the cell membrane, and the body's energy reserve is stored in fat cells.

Fats are divided into two groups - proper fats or lipids and fat-like substances or lipoids. Fats are made up of carbon, hydrogen and oxygen. Fat has complex structure; its components are glycerol (С3Н8О3) and fatty acids, when combined with an ester bond, fat molecules are formed. These are the so-called true fats or triglycerides.

Fatty acids that make up fats are divided into limiting and unsaturated. The former do not have double bonds and are also called saturated, while the latter have double bonds and are called unsaturated. There are also polyunsaturated fatty acids that have two or more double bonds. Such fatty acids are not synthesized in the human body and must be supplied with food, as they are for the synthesis of some important lipoids. The more double bonds, the lower the melting point of fat. Unsaturated fatty acids make fats more liquid. There are many of them in vegetable oil.

Functions of fats:

· Neutral fats (triglycerides):

o are the most important source of energy. When 1 g of a substance is oxidized, the maximum amount of energy is released compared to the oxidation of proteins and carbohydrates. Due to the oxidation of neutral fats, 50% of all energy in the body is formed;

o make up the bulk of animal food and body lipids (10-20% of the body);

o are a component of the structural elements of the cell - the nucleus, cytoplasm, membrane;

o deposited in subcutaneous tissue, protect the body from heat loss, and the surrounding internal organs from mechanical damage. Physiological donation of neutral fats is performed by lipocytes, the accumulation of which occurs in the subcutaneous adipose tissue, omentum, fatty capsules of various organs. An increase in body weight by 20-25% against the norm is considered the maximum allowable physiological limit.

· Phospho- and glycolipids:

o are part of all cells of the body (cellular lipids), especially nerve cells;

o are a ubiquitous component of the body's biological membranes;

o synthesized in the liver and intestinal wall, while the liver determines the level of phospholipids throughout the body, since the release of phospholipids into the blood occurs only in the liver;

Brown fat:

o represents a special adipose tissue, located in the neck and upper back in newborns and infants and makes up about 1-2% of their total body weight. In a small amount (0.1-0.2% of body weight), brown fat is also present in an adult;

o is able to give 20 or more times more heat (per unit mass of its tissue) than ordinary adipose tissue;

o despite the minimum content in the body, it is able to generate 1/3 of all heat generated in the body;

o plays an important role in the body's adaptation to low temperatures;

·Fatty acid:

o are the main products of lipid hydrolysis in the intestine. An important role in the process of absorption of fatty acids is played by bile and the nature of nutrition;

o extremely important for the normal functioning of the body, essential fatty acids that are not synthesized by the body include oleic, linoleic, linolenic and arachidic acids ( daily requirement 10-12 g).

§ Linoleic and lonolenic acids are found in vegetable fats, arachidic - only in animals;

§ Deficiency of essential fatty acids in food leads to a slowdown in the growth and development of the body, a decrease in reproductive function and various skin lesions. The ability of tissues to utilize fatty acids is limited by their insolubility in water, large sizes molecules as well as the structural features of the cell membranes of the tissues themselves. As a result, a significant part of the fatty acids is bound by adipose tissue lipocytes and deposited.

· Complex fats:

o phosphatides and sterols - help maintain a constant composition of the cytoplasm nerve cells, the synthesis of sex hormones and hormones of the adrenal cortex, the formation of certain vitamins (for example, vitamin D).

2.2 Digestion and absorption of fats in the body

Digestion of fat in the human body occurs in the small intestine. Fats are first converted into an emulsion with the help of bile acids. In the process of emulsification, large fat droplets turn into small ones, which significantly increases their total surface area. Enzymes of pancreatic juice - lipases, being proteins, cannot penetrate into fat droplets and break down only fat molecules located on the surface. Under the action of lipase, fat is broken down by hydrolysis to glycerol and fatty acids.

Since a variety of fats are present in food, as a result of their digestion, a large number of types of fatty acids.

The products of fat breakdown are absorbed by the mucous membrane of the small intestine. Glycerin is soluble in water, so it is easily absorbed. Fatty acids, insoluble in water, are absorbed in the form of complexes with bile acids. In cages small intestine choleic acids are broken down into fatty and bile acids. Bile acids from the wall of the small intestine enter the liver and are then released back into the cavity of the small intestine.

The released fatty acids in the cells of the small intestine wall recombine with glycerol, resulting in a new fat molecule. But only fatty acids, which are part of human fat, enter into this process. Thus, human fat is synthesized. This conversion of dietary fatty acids into their own fats is called fat resynthesis.

Resynthesized fats through the lymphatic vessels, bypassing the liver, enter big circle blood circulation and are deposited in the stock in fat depots. The main fat depots of the body are located in the subcutaneous adipose tissue, the greater and lesser omentums, and the perirenal capsule. The fats located here can pass into the blood and, entering the tissues, undergo oxidation there, i.e. used as energy material.

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

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

3 Regulation of fat metabolism

The regulation of fat metabolism in the body occurs under the guidance of the central nervous system. Our emotions have a very strong influence on fat metabolism. Under the influence of various strong emotions, substances enter the bloodstream that activate or slow down the fat metabolism in the body. For these reasons, one should eat in a calm state of mind.

Violation of fat metabolism can occur with a regular lack of vitamins A and B in the diet.

The process of formation, deposition and mobilization from the fat depot is regulated by the nervous and endocrine systems, as well as tissue mechanisms, and is closely related to carbohydrate metabolism. Thus, an increase in the concentration of glucose in the blood reduces the breakdown of triglycerides and activates their synthesis. A decrease in the concentration of glucose in the blood, on the contrary, inhibits the synthesis of triglycerides and enhances their breakdown. Thus, the relationship between fat and carbohydrate metabolism is aimed at providing energy needs organism. With an excess of carbohydrates in food, triglycerides are deposited in adipose tissue, with a shortage of carbohydrates, triglycerides are split with the formation of non-esterified fatty acids, which serve as an energy source.

A number of hormones have a pronounced effect on fat metabolism. Hormones of the adrenal medulla - adrenaline and noradrenaline - have a strong fat-mobilizing effect, therefore, prolonged adrenalinemia is accompanied by a decrease in fat depot. The pituitary somatotropic hormone also has a fat-mobilizing effect. Thyroxine, a thyroid hormone, acts similarly, so hyperfunction of the thyroid gland is accompanied by weight loss.

On the contrary, glucocorticoids, hormones of the adrenal cortex, inhibit the mobilization of fat, probably due to the fact that they slightly increase the level of glucose in the blood.

There is evidence of the possibility of direct nervous influences on fat metabolism. Sympathetic influences inhibit the synthesis of triglycerides and increase their breakdown. Parasympathetic influences, on the contrary, contribute to the deposition of fat.

Nervous influences fat metabolism is controlled by the hypothalamus. With the destruction of the ventromedial nuclei of the hypothalamus, a prolonged increase in appetite and increased fat deposition develop. Irritation of the ventromedial nuclei, on the contrary, leads to loss of appetite and emaciation.

In table. 11.2 summarizes the influence of a number of factors on the mobilization of fatty acids<#"276" src="doc_zip1.jpg" />

Chapter 3

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

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

The metabolism of carbohydrates is central to the metabolism and energy. Complex carbohydrates in food are broken down during digestion into monosaccharides, mainly glucose. Monosaccharides are absorbed from the intestines into the blood and delivered to the liver and other tissues, where they are included in the intermediate metabolism. Part of the incoming glucose in the liver and skeletal muscles is deposited in the form of glycogen or used for other plastic processes. With an excess intake of carbohydrates with food, they can turn into fats and proteins. Another part of glucose undergoes oxidation with the formation of ATP and the release of thermal energy. Two main mechanisms of carbohydrate oxidation are possible in tissues - without the participation of oxygen (anaerobically) and with its participation (aerobically).

3.1 Carbohydrates and their functions

Carbohydrates - organic compounds contained in all tissues of the body in a free form in compounds with lipids and proteins and are the main sources of energy. Functions of carbohydrates in the body:

· Carbohydrates are the direct source of energy for the body.

· Participate in the plastic processes of metabolism.

· They are part of the protoplasm, subcellular and cellular structures, perform a supporting function for cells.

Carbohydrates are divided into 3 main classes: monosaccharides, disaccharides and polysaccharides. Monosaccharides are carbohydrates that cannot be broken down to more simple shapes(glucose, fructose). Disaccharides are carbohydrates that, when hydrolyzed, give two molecules of monosaccharides (sucrose, lactose). Polysaccharides are carbohydrates that, when hydrolyzed, give more than six molecules of monosaccharides (starch, glycogen, fiber).

3.2 Breakdown of carbohydrates in the body

The breakdown of complex food carbohydrates begins in the oral cavity under the action of salivary amylase and maltase enzymes. The optimal activity of these enzymes is manifested in an alkaline environment. Amylase breaks down starch and glycogen, while maltase breaks down maltose. In this case, more low-molecular carbohydrates are formed - dextrins, partially - maltose and glucose.

In the digestive tract, polysaccharides (starch, glycogen; fiber and pectin are not digested in the intestines) and disaccharides under the influence of enzymes are cleaved to monosaccharides (glucose and fructose), which are absorbed into the blood in the small intestine. A significant part of monosaccharides enters the liver and muscles and serve as a material for the formation of glycogen. The process of absorption of monosaccharides in the intestine is regulated by the nervous and hormonal systems. Under the influence of the nervous system, the permeability of the intestinal epithelium, the degree of blood supply to the mucous membrane of the intestinal wall and the speed of movement of the villi can change, as a result of which the rate of entry of monosaccharides into the blood of the portal vein changes. Glycogen is stored in the liver and muscles. As needed, glycogen is mobilized from the depot and converted into glucose, which enters the tissues and is used by them in the process of life.

Liver glycogen is a reserve, i.e. stored in reserve, carbohydrate. Its amount can reach 150-200 g in an adult. The formation of glycogen with a relatively slow entry of glucose into the blood occurs quite quickly, therefore, after administration a small amount carbohydrates increase in blood glucose (hyperglycemia) is not observed. If a large amount of easily digested and rapidly absorbed carbohydrates enters the digestive tract, the blood glucose content increases rapidly. The hyperglycemia developing at the same time is called alimentary, in other words - food. Its result is glucosuria, i.e. the excretion of glucose in the urine<#"justify">3.3 Regulation of carbohydrate metabolism

The main parameter for the regulation of carbohydrate metabolism is to maintain the level of glucose in the blood within the range of 4.4-6.7 mmol/l. Changes in blood glucose are perceived by glucoreceptors, concentrated mainly in the liver and blood vessels, as well as by cells of the ventromedial hypothalamus. Participation of a number of departments of the CNS in the regulation of carbohydrate metabolism has been shown.

The role of the cerebral cortex in the regulation of blood glucose levels illustrates the development of hyperglycemia in students during an exam, in athletes before important competitions, and also during hypnotic suggestion. The central link in the regulation of carbohydrate and other types of metabolism and the place of formation of signals that control glucose levels is the hypothalamus. Hence, the regulatory influences are realized by the autonomic nerves and by the humoral pathway, including endocrine glands.

Insulin, a hormone produced by β-cells of the islet tissue of the pancreas, has a pronounced effect on carbohydrate metabolism. With the introduction of insulin, the level of glucose in the blood decreases. This is due to increased insulin synthesis of glycogen in the liver and muscles and increased consumption of glucose by body tissues. Insulin is the only hormone that lowers the level of glucose in the blood, therefore, with a decrease in the secretion of this hormone, persistent hyperglycemia and subsequent glucosuria (diabetes mellitus, or diabetes mellitus) develop.

An increase in blood glucose levels occurs under the action of several hormones. It is glucagon produced by the alpha cells of the islet tissue of the pancreas; adrenaline - a hormone of the adrenal medulla; glucocorticoids - hormones of the adrenal cortex; growth hormone pituitary gland; thyroxine and triiodothyronine are thyroid hormones. Due to the unidirectional effect on carbohydrate metabolism and functional antagonism to the effects of insulin, these hormones are often referred to as "contrinsular hormones".

Chapter 4

1 Structure of the liver

Liver (hepar) - unpaired organ abdominal cavity, the largest gland in the human body. The human liver weighs one and a half to two kilograms. It is the largest gland in the body. In the abdominal cavity, it occupies the right and part of the left hypochondrium. The liver is dense to the touch, but very elastic: neighboring organs leave clearly visible traces on it. Even external causes, for example mechanical pressure, can cause a change in the shape of the liver. Detoxification takes place in the liver toxic substances entering it with blood from gastrointestinal tract; the most important protein substances of the blood are synthesized in it, glycogen and bile are formed; The liver is involved in lymph formation, plays an essential role in metabolism. The entire liver consists of many prismatic lobules ranging in size from one to two and a half millimeters. Each individual slice contains everything structural elements of the whole organ and is like a liver in miniature. Bile is produced continuously by the liver, but it enters the intestines only as needed. AT certain periods time, the bile duct closes.

The circulatory system of the liver is very peculiar. Blood flows to it not only through the hepatic artery coming from the aorta, but also through the portal vein, which collects venous blood from the abdominal organs. Arteries and veins densely braid the liver cells. The close contact of blood and bile capillaries, as well as the fact that blood flows more slowly in the liver than in other organs, contribute to a more complete metabolism between blood and liver cells. The hepatic veins gradually connect and flow into a large collector - the inferior vena cava, into which all the blood that has passed through the liver flows.

The liver is one of the few organs capable of restoring its original size even with only 25% of normal tissue remaining. In fact, regeneration occurs, but very slowly, and the rapid return of the liver to its original size is more likely due to an increase in the volume of the remaining cells.

4.2 Functions of the liver

The liver is both an organ of digestion, circulation and metabolism of all kinds, including hormonal. It performs over 70 functions. Let's consider the main ones. The most important closely related functions of the liver include general metabolic (participation in interstitial metabolism), excretory and barrier functions. The excretory function of the liver ensures the excretion of more than 40 compounds from the body with bile, both synthesized by the liver itself and captured by it from the blood. Unlike the kidneys, it also excretes substances with a high molecular weight and insoluble in water. Among the substances excreted by the liver in the composition of bile are bile acids, cholesterol, phospholipids, bilirubin, many proteins, copper, etc. The formation of bile begins in the hepatocyte, where some of its components are produced (for example, bile acids), while others are captured from blood and concentrate. Paired compounds are also formed here (conjugation with glucuronic acid and other compounds), which contributes to an increase in the water solubility of the initial substrates. From hepatocytes, bile enters the bile duct system, where it is further formed due to the secretion or reabsorption of water, electrolytes, and some low molecular weight compounds.

The barrier function of the liver is to protect the body from the damaging effects of foreign agents and metabolic products, maintaining homeostasis. The barrier function is carried out due to the protective and neutralizing action of the liver. The protective effect is provided by non-specific and specific (immune) mechanisms. The former are associated primarily with stellate reticuloendotheliocytes, which are the most important constituent part(up to 85%) systems of mononuclear phagocytes. Specific defensive reactions carried out as a result of the activity of lymphocytes lymph nodes liver and the antibodies they synthesize. The neutralizing effect of the liver ensures the chemical transformation of toxic products, both coming from outside and formed during interstitial metabolism. As a result of metabolic transformations in the liver (oxidation, reduction, hydrolysis, conjugation with glucuronic acid or other compounds), the toxicity of these products decreases and (or) their water solubility increases, which makes possible allocation them from the body.

4.3 The role of the liver in metabolism

Considering the metabolism of proteins, fats and carbohydrates, we have repeatedly affected the liver. The liver is the most important body that performs protein synthesis. All blood albumin, the bulk of coagulation factors, protein complexes (glycoproteins, lipoproteins), etc. are formed in it. The most intensive breakdown of proteins also occurs in the liver. It is involved in the metabolism of amino acids, the synthesis of glutamine and creatine; Urea is formed almost exclusively in the liver. The liver plays an important role in lipid metabolism. Basically, triglycerides, phospholipids and bile acids are synthesized in it, a significant part of endogenous cholesterol is formed here, triglycerides are oxidized and acetone bodies are formed; The bile secreted by the liver is essential for the breakdown and absorption of fats in the intestines. The liver is actively involved in the interstitial metabolism of carbohydrates: the formation of sugar, the oxidation of glucose, the synthesis and breakdown of glycogen occur in it. The liver is one of the most important stores of glycogen in the body. The participation of the liver in pigment metabolism is the formation of bilirubin, its capture from the blood, conjugation and excretion into bile. The liver is involved in the exchange biologically active substances- hormones, biogenic amines, vitamins. Here active forms of some of these compounds are formed, they are deposited, inactivated. Closely related to the liver and the metabolism of trace elements, tk. The liver synthesizes proteins that transport iron and copper in the blood and acts as a depot for many of them.

The activity of the liver is influenced by other organs of our body, and most importantly, it is under the constant and unrelenting control of the nervous system. Under a microscope, you can see that the nerve fibers densely braid each hepatic lobule. But the nervous system has more than just a direct effect on the liver. It coordinates the work of other organs that affect the liver. This applies primarily to organs internal secretion. It can be considered proven that the central nervous system regulates the functioning of the liver - directly or through other body systems. It sets the intensity and direction of the processes of liver metabolism in accordance with the needs of the body in this moment. In turn, biochemical processes in the liver cells cause irritation of sensitive nerve fibers and thereby affect the state of the nervous system.

Proteins, fats and carbohydrates are very important for our body. In short, proteins are the basis of all cellular structures, the main building material, fats are an energy and plastic material, carbohydrates are a source of energy in the body. Their correct ratio and timely use is a proper balanced diet, and this, in turn, is a healthy people.

The liver, on the other hand, performs complex and diverse work, which is very important for a healthy metabolism. When nutrients enter the liver, they are converted into new chemical structure, these processed substances are sent to all organs and tissues, where they turn into cells of our body, and some of them are deposited in the liver, forming a kind of depot here. If necessary, they again enter the bloodstream. So the liver is involved in the exchange of each nutrient, and if it is removed, a person will immediately die.

Bibliography:

1.A.A. Markosyan: Physiology;

2.V.M. Pokrovsky: Human Physiology 2003.

Stepan Panov article: Protein metabolism in the human body 2010

Wikipedia

L.A. Chistovich: Human Physiology 1976

N.I. Volkov, Biochemistry of muscular activity 2000. - 504 p.

Lehninger, A. Fundamentals of biochemistry / A. Leninger. - M.: Mir, 1985.

V. Kumar: Pathoanatomy of Robbins and Cotran diseases 2010

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

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

Usually, when you eat a lot of carbohydrates, sugar appears in the urine, and this equalizes the sugar content in the blood.

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

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

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

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

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

Fat metabolism

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

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

Fatty acids are saponified during absorption, i.e., together with alkalis and bile acids, they form soluble complexes that pass through the intestinal mucosa. Already in the cells of the intestinal epithelium, the fat characteristic of this organism is synthesized.

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

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

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

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

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

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

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

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

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

Protein occupies one of the most important places among all organic elements of a living cell. It makes up almost half of the cell mass. In the human body there is a constant exchange of proteins that come with food. In the digestive tract is carried up to amino acids. The latter penetrate into the blood and, having passed through the cells and vessels of the liver, enter the tissues of the internal organs, where they are again synthesized into specific for this body proteins.

Protein metabolism

The human body uses protein as a plastic material. Its need is determined by the minimum volume that balances protein losses. In the body of an adult healthy person, protein metabolism occurs continuously. In case of insufficient intake of these substances with food, ten of the twenty amino acids can be synthesized by the body, while the other ten remain indispensable and must be replenished. Otherwise, there is a violation of protein synthesis, which leads to growth inhibition and weight loss. It should be noted that if at least one organism is missing, it cannot live and function normally.

Stages of protein metabolism

The exchange of proteins in the body occurs as a result of the intake of nutrients and oxygen. There are certain stages, the first of which is characterized by carbohydrates and fats to soluble amino acids, monosaccharides, disaccharides, fatty acids, glycerol and other compounds, after which they are absorbed into the lymph and blood. At the second stage, oxygen is also transported by the blood to the tissues. In this case, they are broken down to final products, as well as the synthesis of hormones, enzymes and constituent components cytoplasm. During the breakdown of substances, energy is released, which is necessary for the natural processes of synthesis and the normalization of the work of the whole organism. The above stages of protein metabolism end with the removal of end products from cells, as well as their transport and lung secretion, kidneys, intestines and sweat glands.

The benefits of proteins for humans

For the human body, the intake of complete proteins is very important, because only specific substances can be synthesized from them. Protein metabolism plays an important role in children's body. After all, he needs a large number of new cells for growth. Insufficient protein intake human body stops growing, and its cells are updated much more slowly. Animal proteins are complete. Of them special value represent the proteins of fish, meat, milk, eggs and other similar food products. Inferior ones are mainly found in plants, so the diet must be designed in such a way as to satisfy all the needs of your body. With an excess of proteins, their excess breaks down. This allows the body to maintain the necessary protein metabolism is very important for human life. When it is violated, the body begins to consume the protein of its own tissues, which leads to serious health problems. Therefore, you should take care of yourself and seriously approach the choice of food.