How a person digests food. Digestive physiology

The main processes of food processing occur as a consequence of digestion within our digestive system. These are all organs whose role is mainly to process food chemically. Also digestive system promotes high-quality absorption of nutrients and stops the intake of harmful food components, neutralizes and removes them.

Thanks to the work of the gastrointestinal tract, food is decomposed to elementary (including chemical) compounds. This is for the best assimilation of food. The digestive tract works like a food processing machine and tirelessly grinds all food consumed by a person, secretes juices for its processing and mixes, subjects it to chemical processing, thanks to which gastric juices cope with the large quantities of food that you consume daily.

Sometimes it is very difficult for the reader to realize how the food you eat is able to maintain the functionality and vital activity of the whole organism, to feed it with useful substances. Now, in a simple form of presentation, we will try to arrange everything "on the shelves" and talk about the physiological process of assimilation and processing of food by different parts of the digestive tract.

Oral cavity

The oral cavity also belongs to the gastrointestinal tract. Starting from the oral cavity, the food that you eat begins to migrate through the body and be absorbed and processed. With the help of the tongue and teeth, the food is mixed and crushed to a homogeneous consistency, then the salivary glands are attacked, with the help of which saliva enters the oral cavity, it moistens the food.

With the help of salivary enzymes called amylase, food begins to decompose. Then the person performs a complex reflex function - swallowing. Swallowing food enters the esophagus.

If a person does not chew food well, it is still not ready for digestion. Food must be thoroughly chewed and chopped, if this is not the case, a person can get gastritis, constipation and suffer from other problems of the digestive tract.

The esophagus is a kind of corridor for a lump of food to pass normally from the mouth to the stomach. The esophagus is a tube with walls that have several layers of muscle fibers.

Inside, this corridor consists of a mucous membrane that has useful property greatly facilitate the passage of food through it. Thanks to the muscle fibers and mucous membranes, food also does not damage the walls of the esophagus. The esophagus tube can expand and contract when the lump needs it to pass into the stomach. So she pushes it through.

Stomach

It is the stomach that grinds, crushes and helps the absorption of food, the stomach performs the main processes for processing consumed food. Thanks to the gastric juice, food is digested as efficiently as possible, and the food is broken down into elementary chemical compounds.

Outwardly, the stomach looks like a pouch that grows or shrinks due to the functional elasticity of the walls that make up it. The capacity of the stomach can be very large. The stomach holds about two kilograms of the food we eat. At the very end of the stomach there is a special valve called the sphincter. It protects from premature entry into the duodenum of food waste.

The first layer of the stomach

The stomach has three main layers. The first layer is the inner one, it is called the "mucous membrane" of the stomach. This first sheath consists of the stomach glands. From the inside, the walls of the stomach are completely covered with epithelial cells. Both the epithelial cells and the stomach wall are very different in structure and perform completely different roles.

Some of them are able to secrete hydrochloric acid with digestive enzymes that secrete gastric juice. Some of the other cells secrete a mucous substance that envelops the stomach walls and protects them from damage.

The mucous membrane has a submucous base, a base. It is created like a track that is laid under the glands and epithelial cells. Many, many small blood vessels, nerves, which make it possible to provide the stomach with blood, nerve cells - to transmit the necessary impulses. For example, painful.

The second layer of the stomach

This second layer is muscles. The stomach has them too. The muscles of the stomach are its thin shell. It is folded in two or even three layers, like puff pastry. The stomach lining helps to grind food into gruel. Just like a mixer. Mixing with gastric juice, food is effectively dissolved and then absorbed by the walls of the stomach.

The third layer of the stomach

And finally, the serous membrane of the stomach is its third layer. It is created in the form of a thin fabric that is lined from the inside abdominal cavity... And not only her, but also internal organs, giving them the opportunity to be dynamic, active, mobile.

What happens in the stomach during digestion?

When food enters the stomach, it is wetted by gastric juice and helps it dissolve. What is gastric juice? It is a liquid, viscous and thick, it is produced by the glands of the gastric mucosa. It is difficult to describe the composition of gastric juice, it contains many components. Its most important ingredients are digestive enzymes and hydrochloric acid. Of course, hydrochloric acid is a rather poisonous and pungent substance that can dissolve many foods. Therefore, the walls of the stomach would dissolve due to the action of hydrochloric acid, if they were not protected by mucus. Digestive enzymes, on the other hand, help the acid dissolve foods more efficiently. These are chemically active substances.

For example, renin is able to make cottage cheese from milk. Lipase is a substance that breaks down fats. But these enzymes do not have very many functions, but they perform them thoroughly. The enzyme pepsin is more active in the stomach - in terms of composition, it complements hydrochloric acid, and can break down proteins taken from plant and animal food in conjunction with it. As a result, simpler chemical compounds are obtained - amino acids and peptides.

When the sphincter of the stomach relaxes, the food that is already ready for the next stage of processing, in the form of gruel, flows further into the lower regions of the digestive tract. And then the remnants of food, which are called chyme, continue to be digested further, but already in the intestines.

Intestines

The work of the intestines is also quite intense, and it is aimed at digesting and pushing food. The intestine performs quite a few roles, and therefore it is designed as a complex natural structure. The intestine has several anatomically determined sections. These are primarily its departments, such as the jejunum, cecum, duodenum, transverse, ascending, ileum, colon, sigmoid and finally rectum. The anus is located in the lower intestine. Through it, feces come out.

How does the intestine work?

It, like the stomach and esophagus, contracts and thus pushes food to its lower section, which ends in the anus. These contractions of the intestine are called peristalsis. And doctors call the role of the intestine in pushing the feces motor, in other words, it is intestinal motility. Have you heard this term? Outwardly, the intestines are like a conduit through which food debris passes.

The intestine also has walls, following the example of the stomach. And they, too, look like sheets laid on top of each other - muscle layers. This makes the intestinal walls elastic, flexible. These walls are the mucous membrane, serous and muscular layers.

When food in the form of a liquid gruel passes through the intestines, at the same time it is broken down with the help of intestinal juice into amino acids and other compounds that have a simple structure. In this form, food is easily absorbed by the elastic and strong intestinal walls. These substances are carried through the blood and nourish the body with the necessary elements that give energy.

Please note: food is digested and absorbed, and also in the form of feces passes into the anus through different parts of the intestine.

Duodenum

This very useful section of the intestine is almost 25 centimeters long. The duodenum plays a noble role - it controls the stomach. He is located next to her, which is very convenient for their interaction.

The duodenum regulates the secretion of hydrochloric acid from the stomach for processing food and also controls its motor and excretory functions.

When there is a lot of hydrochloric acid (high acidity), it becomes dangerous for the condition of the gastric mucosa - it can begin to digest itself, which is also quite painful. Therefore, the duodenum stops this process (secretion of acid by the stomach), transmitting the corresponding signal through the receptors. At the same time, the lower parts of the intestine receive a command about how. that now the food will begin to move towards them - down from the stomach.

Bile also comes from the duodenum to break down food, which facilitates the digestion process. Then all food elements can be digested - fats, carbohydrates, and proteins.

Small intestine

It is very long - from 4 meters to 7 meters. The small intestine follows, like a girlfriend, the duodenum. The small intestine also includes two other areas of the intestine - the ileum and the jejunum. They play important roles in the digestion process. When food reaches these parts of the intestine, the food is chemically processed there by various chemicals, and then begins to be absorbed by the intestinal walls. In particular, those substances that are useful for the body are absorbed.

If we briefly characterize the process of digestion, it will be the movement of the eaten food through the digestive organs, in which food is split into simpler elements. Small substances can be absorbed and assimilated by the body, and then pass into the bloodstream and nourish all organs and tissues, giving them the opportunity to work normally.

Digestion Is a process of mechanical crushing and chemical, mainly enzymatic, splitting of food into substances devoid of species specificity and suitable for absorption and participation in the metabolism of the human body. Food entering the body is processed by enzymes produced by special cells. Complex food structures such as proteins, fats, and carbohydrates are broken down by the addition of water molecules. Proteins break down during digestion to amino acids, fats to glycerin and fatty acids, and carbohydrates to simple sugars. These substances are well absorbed, and then they are synthesized again in tissues and organs into complex compounds.

The length of the human digestive tract is 9 meters. The process of complete processing of food lasts from 24 to 72 hours and is different for all people. The digestive system includes the following organs: the oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, and rectum.

The process of digestion itself is divided into stages of human digestion, and they consist of a head, stomach and intestinal phase.

Head phase of digestion

This is the stage where the recycling process begins. A person sees food and smells, his cerebral cortex is activated, signals of taste and smell begin to enter the hypothalamus and medulla oblongata, which are involved in the digestion process.

A lot of juice is secreted in the stomach, ready to eat, enzymes are produced and saliva is actively secreted. Then the food enters the oral cavity, where it is mechanically ground by chewing with the teeth. At the same time, food is mixed with saliva, interaction with enzymes and microorganisms begins.

A certain amount of food in the process of digestion is already broken down by saliva, from which the taste of food is felt. Digestion in the mouth produces the breakdown of starch into simple sugars by the amylase enzyme found in saliva. Proteins and fats in the mouth do not break down. The whole process in the mouth lasts no more than 15-20 seconds.

The phase of food processing in the stomach of the body

Further, the phase of the digestion process continues in the stomach. This is the widest part of the digestive system, is capable of stretching and holds quite a lot of food. The stomach tends to contract rhythmically, while mixing the incoming food with gastric juice is observed. It contains hydrochloric acid, so it has an acidic environment necessary for the breakdown of food.

Food in the stomach is processed in the process of digestion for 3-5 hours, being digested in every possible way, mechanically and chemically. In addition to hydrochloric acid, pepsin is also used. Therefore, the splitting of proteins into smaller fragments begins: low molecular weight peptides and amino acids. But the breakdown of carbohydrates in the stomach during digestion stops, because amylase stops its action under the pressure of an acidic environment. How does stomach digestion work? Gastric juice contains lipase, which breaks down fats. Hydrochloric acid is of great importance, under its influence enzymes are activated, denaturation and swelling of proteins occurs, the bactericidal property of stomach juice is triggered.

Please note: Carbohydrate food lingers in this organ for 2 hours during digestion, then it moves to the small intestine. But protein and fatty foods are processed in it for 8-10 hours.

Then the food, partially processed by the digestion process and having a liquid or semi-liquid structure, mixed with gastric juice, falls in portions into the small intestine. The stomach contracts during digestion at regular intervals and food is squeezed into the intestines.

Digestive phase in the small intestine of the human body

The logical diagram of food processing in the small intestine is considered the most important in the whole process, because it is there that the most nutrients are absorbed. In this organ, intestinal juice acts, which has an alkaline environment, and consists of bile entering the department, pancreatic juice and fluid from the intestinal walls. Digestion at this stage does not last for everyone for a short time. This is due to a lack of the lactase enzyme that processes milk sugar, so milk is poorly absorbed. Especially in people over the age of 40. More than 20 different enzymes are involved in the intestinal tract for food processing.

The small intestine consists of three parts, passing into each other and depending on the work of the neighbor:

• duodenum;
• skinny;
• ileum.

Exactly at duodenum bile is poured in during digestion from the liver and pancreatic juice, it is their effect that leads to the digestion of food. Pancreatic juice contains fat-dissolving enzymes. Here carbohydrates are broken down to simple sugars and proteins. In this organ there is the greatest assimilation of food, vitamins and nutrients are absorbed by the intestinal walls.

All carbohydrates, fats and parts of proteins in the jejunum and ileum are completely digested under the action of enzymes produced locally. The intestinal mucosa is strewn with villi - enterocytes. It is they who absorb the products of the processing of proteins and carbohydrates, which enter the bloodstream, and the fatty elements into the lymph. Due to the large area of \u200b\u200bthe intestinal walls and the numerous villi, the absorption surface is approximately 500 square meters.

Further, food enters the colon, in which feces are formed, and the mucous membrane of the organ absorbs water and other useful microelements. The colon ends with a straight section, conjugated with the anus.

The role of the liver in food processing in the body

The liver produces bile during digestion from 500 to 1500 ml per day. Bile is thrown into the small intestine and does a great job there: it helps emulsify fats, absorb triglycerides, stimulate lipase activity, improve peristalsis, inactivate pepsin in the duodenum, disinfect, and improve hydrolysis and absorption of proteins and carbohydrates.

This is interesting: Bile does not contain enzymes, but it is required to break down fats and fat-soluble vitamins. If it is produced in a small volume, then the processing and absorption of fats is disrupted, and they leave the body naturally.

How does digestion go without gallbladder and bile?

Recently, surgical removal of the gallbladder is often performed - an organ in the form of a bag for the accumulation and preservation of bile. The liver produces bile continuously, and it is required only at the time of food processing. When food is processed, the duodenum becomes empty and the need for bile disappears.

What happens when there is no bile and what is digestion without one of the main organs? If it is removed before changes have begun in organs interdependent with it, its absence is transferred normally. Bile, continuously produced by the liver, accumulates in its ducts during digestion, and then goes directly to the duodenum.

Important! Bile is thrown there, regardless of the presence of food in it, therefore, immediately after the operation, you need to eat often, but a little. This is required so that there is not enough bile to process a large volume of food. Sometimes the body needs time to learn to live without the gallbladder and the bile it produces, so that it can find a place to accumulate this fluid.

Digestion of food in the large intestine of the body

The remains of unprocessed food then go to the large intestine, where they are digested for at least 10-15 hours. The large intestine measures 1.5 meters and contains three sections: the cecum, the transverse colon, and the rectum. In this organ, the following processes take place: water absorption and microbial metabolism of nutrients. Ballast is of great importance in the processing of food in the colon. It includes non-processed biochemical substances: cellulose, resins, wax, hemicellulose, lignin, gums. The portion of dietary fiber that is not broken down in the stomach and small intestine is processed in the large intestine by microorganisms. Structural chemical composition food affects the duration of absorption of substances in small intestine and his movement along the digestive tract.

In the colon, during digestion, feces are formed, which include unprocessed food residues, mucus, dead cells of the intestinal mucosa, microbes that constantly multiply in the intestine and cause fermentation and bloating.

Breakdown and absorption of nutrients in the body

The cycle of food processing and absorption of the necessary elements from healthy person lasts from 24 to 36 hours. Throughout its entire length, mechanical and chemical influences on food in order to break it down into simple substances that can be absorbed into the blood. It occurs throughout the digestive tract during digestion, the mucous membrane of which is strewn with small villi.

This is interesting: For the normal absorption of fat-soluble foods, bile and fats in the intestines are required. In order to absorb water-soluble substances, such as amino acids, monosaccharides, blood capillaries are used.

We have already said that food is subjected to mechanical and chemical processing. In the oral cavity, the main role is played by preparatory mechanical processing - they turn food into finely ground moist gruel. However, already in the mouth - under the influence of saliva and its enzymes - splitting complex carbohydrates... The starch of bread, potatoes, various groups under the action of the enzyme amylase is converted into maltose. This carbohydrate consists of only two glucose particles, which are immediately broken down by the enzyme maltase to form glucose monosaccharide. We know from life experience that, indeed, if you hold it in your mouth, it will gradually acquire a sweetish taste. However, food usually does not linger in the mouth for a long time, and the saliva, swallowed together with the food lump, continues its work already in the stomach. This is very important, because gastric juice does not work. Its main parts are the enzyme pepsin and gastrixin, which break down, and without which these enzymes practically do not affect proteins. After staying in the stomach for 3-8 hours, food passes into the small intestines, along which it moves for about 6-7 hours, being exposed to the action of enzymes of pancreatic and intestinal juices. Especially great is the value of pancreatic juice, which, as can be seen from the attached table, affects both proteins, and carbohydrates. It is no coincidence that people with a sharply reduced gastric secretion can live and work - they are saved by the activity of the pancreas. There is less pancreatic juice than other juices, but it is the most valuable. However, no matter how valuable pancreatic juice is, without intestinal juice and bile it cannot manifest its strength. On the one hand, in Pavlov's laboratories it was discovered that the trypsin itself, contained in the juice of the pancreas, being obtained directly from its duct, does not act on proteins. As soon as he comes into contact with the intestinal mucosa, at least with that piece of it that surrounds the duct opening sewn to the skin, and trypsin acquires all its strength. It turned out that the glands of the intestine produce an enzyme enzyme - enterokinase, which converts trypsinogen into its active form. Let us recall that pepsin itself is not very active and acquires strength only where hydrochloric acid is added to it. Both are biologically justified. If pepsin and trypsin were produced immediately in an active form, they would break down the proteins of the cells that produce them. stomach and pancreas would fall prey to their own juices.

Thus, on the one hand, intestinal juice helps the pancreatic juice, on the other hand, bile helps it. It is she who allows you to normally digest and absorb fats. Although there are no enzymes in bile, it activates the action of the fat-breaking enzymes in pancreatic juice. It is not for nothing that in case of liver diseases, the body poorly absorbs fatty foods.

Returning to the intestinal juice, it should be pointed out that, in addition to the help of trypsin, it also has an independent meaning. It is he who breaks down one of the most important food products -. Only the intestinal juice breaks down the most important carbohydrate of milk - milk sugar,.

We have already said that the chemical processing of food is facilitated by its mechanical processing, carried out due to the movements of the walls of the digestive tract. There are mainly movements of two types. First, there are so-called pendulum contractions, in which a certain segment of the intestine becomes thinner and longer, then thicker and shorter. At the same time, the food gruel contained in it is vigorously mixed. Secondly, the so-called peristalsis occurs - in the direction from the stomach to the intestine, muscle contraction waves run along the entire length of the digestive tube, pushing the food mass further and further along the narrow "corridor" of the digestive tract. In total, food is spent on the passage of this entire route for about a day. Herbivores, which have much longer intestines, have a much longer transit time. Food residues are thrown away from them a few days after eating (in a sheep - after a week).

As a result of the process, about 90% of the valuable nutrients contained in food are broken down and converted into products that the body can absorb. The importance of the small intestine is not only in. the fact that the process of digestion of food is completed in it, but also that it is absorbed here. The mucous membrane of the intestine has a velvety appearance due to the mass of its tiny protrusions, which are called the villi. This increases the surface of the mucous membrane by 300-500 times. Each villus contains blood and lymphatic vessels, into which food digestion products are absorbed and absorbed, as well as a number of other food substances that do not need to be digested - water, salts and vitamins. There are also some substances that are sometimes harmful to the body.

Digestive juice	Its enzymes	The action of these enzymes	Notes
(about 1 liter per day)	Amylase	Breaks down starch to maltose	Mostly act in the stomach
	Maltase	Breaks down maltose to glucose
(about 3 liters per day)		Breaks down proteins to albumosis and peptones (intermediate protein breakdown products)	Only works in an acidic environment
		Breaks down fats	Weak enzyme
Pancreatic juice (up to 2 liters per day)		Breaks down proteins into amino acids	Activated by enterokinase
	Lipase	Breaks down fats (the most powerful enzyme of its kind)	Activated by bile
	Amylase Maltase	Similar to those of saliva
Intestinal juice (about 3.5 liters per day)	Enterokinase	Enzyme enzyme, activates trypsin
	Erepsin	Breaks down albumoses and peptones to amino acids (as if "completing" what was started by pepsin)
	Lipase	Breaks down fats	Weak enzyme
	Invertin	Breaks down sugar into glucose and fructose
	Lactase	Breaks down milk sugar into glucose and
	Amylase Maltase	Similar to those of saliva and pancreatic juice
(about 1 liter per day)	-	-	Promotes the digestion and absorption of fats

Currently, nutrition means difficult process receipt, digestion, absorption and assimilation in the body of substances (nutrients) necessary to meet the energy and plastic needs of the body, including the regeneration of cells and tissues, regulation of various functions of the body. Digestion is a combination of physicochemical and physiological processes that ensure the breakdown of complex nutrients entering the body into simple chemical compounds that can be absorbed and assimilated in the body.

There is no doubt that food entering the body from the outside, usually consisting of native polymeric material (proteins, fats, carbohydrates), must be destructed and hydrolyzed to elements such as amino acids, hexoses, fatty acids, etc., which are directly involved in metabolic processes. The transformation of the starting substances into resorbable substrates occurs in stages as a result of hydrolytic processes involving various enzymes.

Recent advances in basic research the work of the digestive system has significantly changed the traditional ideas about the activity of the "digestive conveyor". In accordance with the modern concept, digestion refers to the processes of food assimilation from its entry into the gastrointestinal tract to its inclusion in intracellular metabolic processes.

A multicomponent digestive conveyor system consists of the following steps:

1. The entry of food into the oral cavity, its grinding, wetting of the food lump and the beginning of cavity hydrolysis. Overcoming the pharyngeal sphincter and entering the esophagus.

2. The entry of food from the esophagus through the cardiac sphincter into the stomach and its temporary deposition. Active mixing of food, its grinding and grinding. Hydrolysis of polymers by gastric enzymes.

3. Entering the food mixture through the antral sphincter into the duodenum. Mixing food with bile acids and pancreatic enzymes. Homeostasis and chyme formation involving intestinal secretion. Hydrolysis in the intestinal cavity.

4. Transport of polymers, oligo- and monomers through the parietal layer of the small intestine. Hydrolysis in the parietal layer by pancreatic and enterocytic enzymes. Transport of nutrients to the glycocalyx zone, sorption - desorption on the glycocalyx, binding to acceptor glycoproteins and active centers of pancreatic and enterocytic enzymes. Hydrolysis of nutrients in the brush border of enterocytes (membrane digestion). Delivery of hydrolysis products to the base of microvilli of enterocytes into the zone of formation of endocytic invaginations (with the possible participation of forces of cavity pressure and capillary forces).

5. Transfer of nutrients into blood and lymphatic capillaries by micropinocytosis, as well as diffusion through fenestra of capillary endothelial cells and through the intercellular space. The entry of nutrients through the portal system into the liver. Delivery of nutrients by lymph and blood flow to tissues and organs. Transport of nutrients through cell membranes and their inclusion in plastic and energy processes.

What is the role of various parts of the digestive tract and organs in ensuring the processes of digestion and absorption of nutrients?

In the oral cavity, food is mechanically crushed, moistened with saliva and prepared for further transport, which is ensured by the fact that food nutrients are converted into a more or less homogeneous mass. With movements, mainly of the lower jaw and tongue, a food lump is formed, which is then swallowed and, in most cases, very quickly reaches the stomach cavity. Chemical processing of nutrients in the oral cavity is usually not very important. Although saliva contains a number of enzymes, their concentration is very low. Only amylase can play a role in the preliminary breakdown of polysaccharides.

Food is retained in the stomach cavity and then slowly, in small portions, moves into the small intestine. Apparently, the main function of the stomach is depository. Food quickly accumulates in the stomach and is then gradually utilized by the body. This is confirmed a large number observations of patients with a removed stomach. The main disorder characteristic of these patients is not the shutdown of the stomach's own digestive activity, but a violation of the depositing function, that is, the gradual evacuation of nutrients into the intestine, which manifests itself in the form of the so-called "dumping syndrome". The stay of food in the stomach is accompanied by enzymatic processing, while the gastric juice contains enzymes that carry out the initial stages of protein breakdown.

The stomach is considered as an organ of peptic-acid digestion, since it is the only part of the alimentary canal where enzymatic reactions take place in a sharply acidic environment. The stomach glands secrete several proteolytic enzymes. The most important of these are pepsins and, in addition, chymosin and parapepsin, which disaggregate the protein molecule and only to a small extent cleave peptide bonds. The effect of hydrochloric acid on food seems to be of great importance. In any case, the acidic environment of gastric contents not only creates optimal conditions for the action of pepsins, but also promotes protein denaturation, causes swelling of the food mass, increases the permeability of cell structures, thereby favoring subsequent digestive processing.

Thus, the salivary glands and stomach play a very limited role in the digestion and breakdown of food. Each of these glands, in fact, acts on one of the types of nutrients (salivary glands - on polysaccharides, stomach - on proteins), and within limited limits. At the same time, the pancreas secretes a wide variety of enzymes that hydrolyze all nutrients. The pancreas acts with the help of the enzymes it produces on all types of nutrients (proteins, fats, carbohydrates).

The enzymatic action of the secretion of the pancreas is realized in the cavity of the small intestine, and this fact alone makes us believe that intestinal digestion is the most essential stage in the processing of nutrients. Here, into the cavity of the small intestine, bile also enters, which, together with pancreatic juice, neutralizes the acidic gastric chyme. The enzymatic activity of bile is low and, in general, does not exceed that found in blood, urine, and other non-digestive fluids. At the same time, bile and, in particular, its acids (cholic and deoxycholic) perform a number of important digestive functions... It is known, in particular, that bile acids stimulate the activity of some pancreatic enzymes. This is most clearly proved in relation to pancreatic lipase, to a lesser extent it concerns amylase and proteases. In addition, bile stimulates intestinal peristalsis and appears to have a bacteriostatic effect. But most important is the participation of bile in the absorption of nutrients. Bile acids are essential for the emulsification of fats and for the absorption of neutral fats, fatty acids, and possibly other lipids.

It is believed that intestinal cavity digestion is a process that takes place in the lumen of the small intestine under the influence, mainly, of pancreatic secretions, bile and intestinal juice. Intra-intestinal digestion is carried out due to the fusion of part of the transport vesicles with lysosomes, cisterns of the endoplasmic reticulum and the Golgi complex. The participation of nutrients in intracellular metabolism is assumed. There is a fusion of transport vesicles with the basolateral membrane of enterocytes and the release of the contents of the vesicles into the intercellular space. Thus, a temporary deposition of nutrients and their diffusion along the concentration gradient through the basement membrane of enterocytes into the lamina propria of the mucous membrane of the small intestine is achieved.

Intensive study of the processes of membrane digestion made it possible to characterize the activity of the food-and-cooking-transport conveyor in the small intestine quite fully. According to the prevailing concepts today, enzymatic hydrolysis of food substrates is sequentially carried out in the cavity of the small intestine (cavity digestion), in the supraepithelial layer of mucous overlays (parietal digestion), on the membranes of the brush border of enterocytes (membrane digestion) and after the penetration of incompletely cleaved substrates into the enterocyte intracellular digestion).

The initial stages of biopolymer hydrolysis are carried out in the cavity of the small intestine. In this case, food substrates that have not undergone hydrolysis in the intestinal cavity, and the products of their initial and intermediate hydrolysis, diffuse through the immiscible layer of the liquid phase of the chyme (autonomous near-membrane layer) into the zone of the brush border, where membrane digestion is carried out. Large-molecular substrates are hydrolyzed by pancreatic endohydrolases adsorbed predominantly on the glycocalyx surface, while intermediate hydrolysis products are hydrolyzed by exohydrolases translocated on the outer surface of the brush border microvilli membranes. Due to the conjugation of the mechanisms that carry out the final stages of hydrolysis and the initial stages of transport through the membrane, the products of hydrolysis formed in the membrane digestion zone are absorbed and enter the internal environment of the body.

The digestion and absorption of essential nutrients is carried out as follows.

The digestion of proteins in the stomach occurs when pepsinogens are converted into pepsins in an acidic medium (optimum pH 1.5-3.5). Pepsins cleave bonds between aromatic amino acids adjacent to carboxyl amino acids. They are inactivated in an alkaline environment, the cleavage of peptides by pepsins stops after the chyme enters the small intestine.

In the small intestine, polypeptides are further degraded by proteases. Basically, the cleavage of peptides is carried out by pancreatic enzymes: trypsin, chymotrypsin, elastase and carboxypeptidases A and B. Enterokinase converts trypsinogen into trypsin, which then activates other proteases. Trypsin cleaves polypeptide chains at the junctions of basic amino acids (lysine and arginine), while chymotrypsin breaks down bonds aromatic amino acids (phenylalanine, tyrosine, tryptophan). Elastase cleaves the bonds of aliphatic peptides. These three enzymes are endopeptidases because they hydrolyze the internal bonds of peptides. Carboxypeptidases A and B are exopeptidases, since only the terminal carboxyl groups of predominantly neutral and basic amino acids are cleaved off, respectively. During proteolysis carried out by pancreatic enzymes, oligopeptides and some free amino acids are cleaved. Microvilli of enterocytes have on their surface endopeptidases and exopeptidases, which break down oligopeptides to amino acids, di- and tripeptides. Absorption of di- and tripeptides is carried out using a secondary active transport. These products are then degraded to amino acids by intracellular peptidases of the enterocytes. Amino acids are absorbed according to the principle of co-transport with sodium at the apical portion of the membrane. Subsequent diffusion through the basolateral membrane of enterocytes occurs against the concentration gradient, and amino acids enter the capillary plexus of the intestinal villi. The types of amino acids carried are distinguished: neutral transporter (transporting neutral amino acids), basic (transporting arginine, lysine, histidine), dicarboxyl (transporting glutamate and aspartate), hydrophobic (transporting phenylalanine and methionine), iminotransporter (transporting proline and hydroxyproline).

In the intestine, only those carbohydrates are broken down and absorbed, on which the corresponding enzymes act. Indigestible carbohydrates (or dietary fiber) cannot be assimilated because there are no special enzymes for this. However, their catabolism by bacteria of the large intestine is possible. Food carbohydrates are composed of disaccharides: sucrose (common sugar) and lactose (milk sugar); monosaccharides - glucose and fructose; vegetable starches - amylose and amylopectin. Another food carbohydrate, glycogen, is a polymer of glucose.

Enterocytes are unable to transport carbohydrates larger than monosaccharides. therefore most of carbohydrates must be broken down before being absorbed. Under the action of saliva amylase, di- and tripolymers of glucose (maltose and maltotriose, respectively) are formed. Salivary amylase is inactivated in the stomach, since the optimum pH for its activity is 6.7. Pancreatic amylase continues the hydrolysis of carbohydrates to maltose, maltotriose and terminal dextrans in the small intestine cavity. Microvilli of enterocytes contain enzymes that break down oligo- and disaccharides to monosaccharides for their absorption. Glucoamylase cleaves bonds at the uncleaved ends of oligosaccharides that are formed when amylopectin is cleaved by amylase. This results in the formation of the most readily cleavable tetrasaccharides. The sugar-isomaltase complex has two catalytic sites: one with sucrase activity, the other with isomaltase activity. The isomaltase site converts tetrasaccharides to maltotriose. Isomaltase and sucrase cleave glucose from the unreduced ends of maltose, maltotriose, and terminal dextrans. In this case, sucrase breaks down the disaccharide sucrose to fructose and glucose. In addition, the microvilli of enterocytes also contain lactase, which breaks down lactose to galactose and glucose.

After the formation of monosaccharides, their absorption begins. Glucose and galactose are transported to enterocytes together with sodium via the sodium-glucose transporter, while glucose absorption increases significantly in the presence of sodium and is impaired in its absence. Fructose enters the cell through the apical portion of the membrane by diffusion. Galactose and glucose pass through the basolateral part of the membrane with the help of carriers; the mechanism of fructose release from enterocytes is less studied. Monosaccharides enter the portal vein through the capillary plexus of the villi and then into the bloodstream.

Fats in food are mainly represented by triglycerides, phospholipids (lecithin) and cholesterol (in the form of its esters). For the full digestion and absorption of fats, a combination of several factors is necessary: \u200b\u200bnormal functioning of the liver and biliary tract, the presence of pancreatic enzymes and alkaline pH, the normal state of enterocytes, the intestinal lymphatic system and regional intestinal-hepatic circulation. The absence of any of these components leads to impaired fat absorption and steatorrhea.

Most of the digestion of fats takes place in the small intestine. However, the initial lipolysis process can take place in the stomach under the action of gastric lipase at an optimum pH of 4-5. Gastric lipase breaks down triglycerides into fatty acids and diglycerides. It is resistant to the effects of pepsin, however, it is destroyed by the action of pancreatic protases in the alkaline environment of the duodenum, its activity is also reduced by the action of bile salts. Gastric lipase is of little value compared to pancreatic lipase, although it has some activity, especially in the antrum, where mechanical stirring of the chyme produces tiny fat droplets, which increases the surface area of \u200b\u200bfat digestion.

After chyme enters the duodenum, further lipolysis occurs, including several sequential stages. First, triglycerides, cholesterol, phospholipids and lipid cleavage products by gastric lipase merge into micelles under the action of bile acids, micelles are stabilized by phospholipids and monoglycerides in an alkaline medium. Then the colipase secreted by the pancreas acts on the micelles and serves as the point of application of the action of pancreatic lipase. In the absence of colipase, pancreatic lipase has weak lipolytic activity. The binding of colipase to micelles is improved by the action of pancreatic phospholipase A on micelle lecithin. In turn, for the activation of phospholipase A and the formation of lysolecithin and fatty acids, the presence of bile salts and calcium is necessary. After hydrolysis of lecithin, the triglycerides of the micelles become available for digestion. The pancreatic lipase then attaches to the colipase-micelle junction and hydrolyzes the 1- and 3-bonds of triglycerides to form monoglyceride and fatty acid. The optimum pH for pancreatic lipase is 6.0-6.5. Another enzyme, pancreatic esterase, hydrolyzes the bonds of cholesterol and fat-soluble vitamins with fatty acid esters. The main products of lipid cleavage by pancreatic lipase and esterase are fatty acids, monoglycerides, lysolecithin and cholesterol (non-esterified). The rate of entry of hydrophobic substances into microvilli depends on their solubilization in micelles in the intestinal lumen.

Fatty acids, cholesterol and monoglycerides enter enterocytes from micelles by passive diffusion; although long chain fatty acids can also be transported by surface binding protein. Since these components are fat-soluble and much finer than undigested triglycerides and cholesterol esters, they easily pass through the enterocyte membrane. In the cell, long-chain fatty acids (more than 12 carbon atoms) and cholesterol are transported by binding proteins in the hydrophilic cytoplasm to the endoplasmic reticulum. Cholesterol and fat-soluble vitamins are transported by a sterol carrier protein to the smooth endoplasmic reticulum, where cholesterol is re-esterified. Long-chain fatty acids are transported through the cytoplasm by a special protein, the degree of their entry into the rough endoplasmic reticulum depends on the amount of fat in the food.

After resynthesis of esters of cholesterol, triglycerides and lecithin in the endoplasmic reticulum, they form lipoproteins, combining with apolipoproteins. Lipoproteins are divided according to size, lipid content and the type of apoproteins that make up them. Chylomicrons and very low density lipoproteins are larger and consist mainly of triglycerides and fat-soluble vitamins, while low-density lipoproteins are smaller and contain predominantly esterified cholesterol. High density lipoproteins are the smallest in size and contain mainly phospholipids (lecithin). Formed lipoproteins exit through the basolateral membrane of enterocytes in vesicles, then they enter the lymphatic capillaries. Medium and short chain fatty acids (less than 12 carbon atoms) can enter the portal vein system directly from enterocytes without generating triglycerides. In addition, short-chain fatty acids (butyrate, propionate, etc.) are formed in the colon from undigested carbohydrates under the action of microorganisms and are an important source of energy for the cells of the colon mucosa (colonocytes).

Summarizing the presented information, it should be recognized that knowledge of physiology and biochemistry of digestion allows to optimize the conditions for artificial (enteral and oral) nutrition, based on the basic principles of the digestive conveyor.

Nutrition is the most important factor aimed at maintaining and ensuring such basic processes as growth, development and the ability to be active. These processes can be supported using only a balanced diet. Before you start addressing the basics, you need to become familiar with the digestion processes in the body.

Digestion - a complex physiological and biochemical process, during which the food taken in the digestive tract undergoes physical and chemical changes.

Digestion is the most important physiological process, as a result of which complex food substances of food under the influence of mechanical and chemical processing are converted into simple, soluble and, therefore, assimilable substances. Their further path is the use as a building and energy material in the human body.

Physical changes in food consist in its crushing, swelling, dissolution. Chemical - in the sequential degradation of nutrients as a result of the action on them of the components of digestive juices, secreted into the cavity of the digestive tract by its glands. The most important role in this belongs to hydrolytic enzymes.

Digestion types

Depending on the origin of hydrolytic enzymes, digestion is divided into three types: intrinsic, symbiotic, and autolytic.

Your own digestion carried out by enzymes synthesized by the body, its glands, enzymes of saliva, stomach and pancreatic juices, epithelium of the intestinal tract.

Symbiotic digestion - hydrolysis of nutrients due to enzymes synthesized by symbionts of the macroorganism - bacteria and protozoa of the digestive tract. Symbiotic digestion is carried out in humans in the large intestine. Due to the lack of a corresponding enzyme in the secretions of the glands, food fiber in humans is not hydrolyzed (this is a certain physiological meaning - the preservation of dietary fiber, which plays an important role in intestinal digestion), therefore, its digestion by symbiont enzymes in the colon is an important process.

As a result of symbiotic digestion, secondary nutrients are formed, in contrast to the primary ones, which are formed as a result of their own digestion.

Autolytic digestion carried out by enzymes that are introduced into the body as part of the food intake. The role of this digestion is essential in the case of insufficiently developed own digestion. In newborns, their own digestion is not yet developed, so the nutrients in breast milk are digested by enzymes that enter the infant's digestive tract in breast milk.

Depending on the localization of the process of hydrolysis of nutrients, digestion is divided into intra- and extracellular.

Intracellular digestion consists in the fact that substances transported into the cell by phagocytosis are hydrolyzed by cellular enzymes.

Extracellular digestion It is divided into a cavity, which is carried out in the cavities of the digestive tract by enzymes of saliva, gastric juice and pancreatic juice, and parietal. Parietal digestion occurs in the small intestine with the participation of a large number of intestinal and pancreatic enzymes on a colossal surface formed by folds, villi and microvilli of the mucous membrane.

Figure: Digestion stages

Currently, the digestion process is considered as a three-stage: cavity digestion - parietal digestion - absorption... Cavity digestion consists in the initial hydrolysis of polymers to the stage of oligomers, the parietal digestion provides further enzymatic depolymerization of oligomers, mainly to the stage of monomers, which are then absorbed.

The correct sequential work of the elements of the digestive conveyor in time and space is ensured by regular processes at various levels.

Enzymatic activity is characteristic of each part of the digestive tract and is maximum at a certain pH of the medium. For example, in the stomach, the digestive process is carried out in an acidic environment. The acidic contents passing into the duodenum are neutralized, and intestinal digestion occurs in a neutral and slightly alkaline environment created by secretions secreted into the intestine - bile, pancreatic and intestinal juices, which inactivate gastric enzymes. Intestinal digestion occurs in a neutral and slightly alkaline environment, first as cavity and then parietal digestion, which ends with the absorption of hydrolysis products - nutrients.

The degradation of nutrients by the type of cavity and parietal digestion is carried out by hydrolytic enzymes, each of which has a specificity expressed to one degree or another. The set of enzymes in the secretions of the digestive glands has specific and individual characteristics, is adapted to the digestion of the food that is characteristic of a given type of animal, and so nutrientsthat prevail in the diet.

Digestion process

The digestion process is carried out in the gastrointestinal tract, the length of which is 5-6 m. The digestive tract is a tube, expanded in some places. The structure of the gastrointestinal tract is the same throughout the entire length, it has three layers:

• outer - serous, dense membrane, which mainly has a protective function;
• medium - muscle tissue participates in the contraction and relaxation of the organ wall;
• inner - a membrane covered with mucous epithelium, allows simple food substances to be absorbed through its thickness; The mucous membrane often contains glandular cells that produce digestive juices or enzymes.

Enzymes - substances of protein nature. In the gastrointestinal tract, they have their own specificity: proteins are cleaved only under the influence of proteases, fats - lipases, carbohydrates - carbohydrases. Each enzyme is active only at a certain pH of the environment.

Functions of the gastrointestinal tract:

• Motor, or motor - due to the middle (muscular) membrane of the digestive tract, muscle contraction-relaxation carries out the capture of food, chewing, swallowing, stirring and moving food along the alimentary canal.
• Secretory - due to digestive juices, which are produced by glandular cells located in the mucous (inner) membrane of the canal. These secrets contain enzymes (reaction accelerators) that chemically process food (hydrolysis of food substances).
• The excretory (excretory) function carries out the secretion of metabolic products by the digestive glands into the gastrointestinal tract.
• The absorption function is the process of assimilation of nutrients through the wall of the gastrointestinal tract into the blood and lymph.

Gastrointestinal tract starts at oral cavity, then food enters the pharynx and esophagus, which carry out only a transport function, the food lump descends into the stomach, then into the small intestine, consisting of the duodenum, jejunum and ileum, where the final hydrolysis (splitting) of food substances mainly occurs and they are absorbed through the intestinal wall into the blood or lymph. The small intestine becomes the large intestine, where there is practically no digestion process, but the functions of the large intestine are also very important for the body.

Digestion in the mouth

Further digestion in other parts of the gastrointestinal tract depends on the process of digestion of food in the oral cavity.

The initial mechanical and chemical processing of food takes place in the oral cavity. It includes chopping food, wetting it with saliva, analyzing the palatability, the initial breakdown of food carbohydrates and the formation of a food lump. The stay of the food lump in the oral cavity is 15-18 seconds. Food in the oral cavity excites the taste, tactile, and temperature receptors of the oral mucosa. This reflexively causes the activation of secretion not only salivary glands, but also the glands located in the stomach, intestines, as well as the secretion of pancreatic juice and bile.

Mechanical processing of food in the oral cavity is carried out using chewing. The act of chewing involves the upper and lower jaws with teeth, chewing muscles, oral mucosa, soft palate. While chewing lower jaw moves in horizontal and vertical planes, the lower teeth are in contact with the upper ones. In this case, the front teeth bite off the food, and the molars crush and grind it. Contraction of the muscles in the tongue and cheeks allows food to flow between the teeth. The contraction of the lip muscles prevents food from falling out of the mouth. The act of chewing is carried out reflexively. Food irritates the receptors in the oral cavity, the nerve impulses from which on the afferent nerve fibers the trigeminal nerve enters the chewing center, located in the medulla oblongata, and excites it. Further, along the efferent nerve fibers of the trigeminal nerve, nerve impulses enter the masticatory muscles.

In the process of chewing, the taste of food is evaluated and its edibility is determined. The more completely and intensively the chewing process is carried out, the more actively the secretory processes proceed both in the oral cavity and in the lower parts of the digestive tract.

The secret of the salivary glands (saliva) is formed by three pairs of large salivary glands (submandibular, sublingual and parotid) and small glands located in the mucous membrane of the cheeks and tongue. 0.5-2 liters of saliva is formed per day.

The functions of saliva are as follows:

• Wetting food, dissolving solids, soaking with mucus and forming a food lump. Saliva facilitates the swallowing process and contributes to the formation of taste sensations.
• Enzyme breakdown of carbohydrates due to the presence of a-amylase and maltase. The enzyme a-amylase breaks down polysaccharides (starch, glycogen) to oligosaccharides and disaccharides (maltose). The action of amylase inside the food lump continues even when it enters the stomach as long as a slightly alkaline or neutral environment remains in it.
• Protective function associated with the presence of antibacterial components in saliva (lysozyme, immunoglobulins of various classes, lactoferrin). Lysozyme, or muramidase, is an enzyme that breaks down the cell wall of bacteria. Lactoferrin binds iron ions, which are necessary for the vital activity of bacteria, and thus stops their growth. Mucin also performs a protective function, as it protects the oral mucosa from the damaging effects of food (hot or sour drinks, hot spices).
• Participation in the mineralization of tooth enamel - calcium enters tooth enamel from saliva. It contains proteins that bind and transport Ca 2+ ions. Saliva protects teeth from caries development.

The properties of saliva depend on the diet and type of food. More viscous saliva is produced when you eat solid and dry foods. When inedible, bitter or acidic substances enter the oral cavity, a large amount of liquid saliva is released. The enzymatic composition of saliva can also change depending on the amount of carbohydrates in the food.

Regulation of salivation. Swallowing. The regulation of salivation is carried out by autonomic nerves that innervate the salivary glands: parasympathetic and sympathetic. When excited parasympathetic nerve salivary gland a large amount of liquid saliva with a low content of organic substances (enzymes and mucus) is formed. When excited sympathetic nerve a small amount of viscous saliva is formed, containing a lot of mucin and enzymes. The activation of salivation when eating first occurs by the conditioned reflex mechanism at the sight of food, preparation for its intake, inhalation of food aromas. At the same time, nerve impulses from the visual, olfactory, auditory receptors along the afferent nerve pathways enter the salivary nuclei of the medulla oblongata (center of salivation), which send efferent nerve impulses along parasympathetic nerve fibers to the salivary glands. The entry of food into the oral cavity excites the receptors of the mucous membrane and this ensures the activation of the process of salivation by the mechanism of an unconditioned reflex. Inhibition of the activity of the center of salivation and a decrease in the secretion of the salivary glands occurs during sleep, with fatigue, emotional arousal, as well as with fever, dehydration of the body.

Digestion in the oral cavity ends with the act of swallowing and the entry of food into the stomach.

Swallowing is a reflex process and consists of three phases:

• 1st phase - oral - is arbitrary and consists in the receipt of the food lump formed in the process of chewing on the root of the tongue. Further, the muscles of the tongue contract and the food lump is pushed into the pharynx;
• 2nd phase - pharyngeal - is involuntary, carried out quickly (within approximately 1 s) and is under the control of the center of swallowing of the medulla oblongata. At the beginning of this phase, contraction of the muscles of the pharynx and soft palate raises palatine curtain and closes the entrance to nasal cavity... The larynx moves up and forward, which is accompanied by the lowering of the epiglottis and closing the entrance to the larynx. At the same time, the muscles of the pharynx contract and the upper esophageal sphincter relaxes. As a result, food enters the esophagus;
• 3rd phase - esophageal - slow and involuntary, occurs due to peristaltic contractions of the esophageal muscles (contraction of the circular muscles of the esophageal wall above the food bolus and longitudinal muscles located below the food bolus) and is under the control of the vagus nerve. The speed of food movement along the esophagus is 2 - 5 cm / s. After the lower esophageal sphincter relaxes, food enters the stomach.

Digestion in the stomach

The stomach is a muscular organ where food is deposited, mixed with gastric juice and moved to the outlet of the stomach. The gastric mucosa has four types of glands that secrete gastric juice, hydrochloric acid, enzymes, and mucus.

Figure: 3. Digestive tract

Hydrochloric acid imparts acidity to gastric juice, which activates the enzyme pepsinogen, converting it into pepsin, participating in protein hydrolysis. The optimal acidity of gastric juice is 1.5-2.5. In the stomach, protein is broken down to intermediate products (albumoses and peptones). Fats are broken down by lipase only when they are in an emulsified state (milk, mayonnaise). Carbohydrates are practically not digested there, since carbohydrate enzymes are neutralized by the acidic contents of the stomach.

During the day, from 1.5 to 2.5 liters of gastric juice is secreted. Food in the stomach takes 4 to 8 hours to digest, depending on the composition of the food.

Mechanism of secretion of gastric juice Is a complex process, it is divided into three phases:

• the cerebral phase, acting through the brain, involves both an unconditioned and a conditioned reflex (sight, smell, taste, food intake into the oral cavity);
• gastric phase - when food enters the stomach;
• the intestinal phase, when certain types of food (meat broth, cabbage juice, etc.), entering the small intestine, cause the secretion of gastric juice.

Digestion in the duodenum

From the stomach, small portions of food gruel enter the initial section of the small intestine - the duodenum, where the food gruel is actively affected by pancreatic juice and bile acids.

In the duodenum from the pancreas, pancreas juice is supplied, which has an alkaline reaction (pH 7.8-8.4). The juice contains enzymes trypsin and chymotrypsin, which break down proteins - into polypeptides; amylase and maltase break down starch and maltose to glucose. Lipase affects only emulsified fats. The emulsification process takes place in the duodenum in the presence of bile acids.

Bile acids are a component of bile. Bile is produced by the cells of the largest organ - the liver, which weighs from 1.5 to 2.0 kg. The liver cells constantly produce bile, which accumulates in gallbladder... As soon as the food gruel reaches the duodenum, bile from the gallbladder enters the intestines through the ducts. Bile acids emulsify fats, activate fat enzymes, enhance the motor and secretory functions of the small intestine.

Digestion in the small intestine (jejunum, ileum)

The small intestine is the longest section of the digestive tract, its length is 4.5-5 m, diameter is from 3 to 5 cm.

Intestinal juice is a secret of the small intestine, the reaction is alkaline. The intestinal juice contains a large number of enzymes involved in digestion: peitidase, nuclease, enterokinase, lipase, lactase, sucrase, etc. The small intestine, due to the different structure of the muscle layer, has an active motor function (peristalsis). This allows the gruel to move through the true intestinal lumen. This is facilitated by the chemical composition of food - the presence of fiber and dietary fiber.

According to the theory of intestinal digestion, the process of assimilation of nutrients is divided into cavity and parietal (membrane) digestion.

Cavity digestion is present in all cavities of the gastrointestinal tract due to digestive secretions - gastric juice, pancreatic and intestinal juice.

Parietal digestion is present only in a certain segment of the small intestine, where the mucous membrane has a bulge or villi and microvilli that increase the inner surface of the intestine by 300-500 times.

The enzymes involved in the hydrolysis of food substances are located on the surface of microvilli, which significantly increases the efficiency of the absorption of food substances in this area.

The small intestine is an organ where most of the nutrients soluble in water, passing through the intestinal wall, are absorbed into the blood, fats initially enter the lymph, and then into the blood. All nutrients through the portal vein enter the liver, where, cleared of the toxic substances of digestion, they are used to nourish organs and tissues.

Digestion in the large intestine

The movement of intestinal contents in the colon is up to 30-40 hours. Digestion in the large intestine is practically absent. Here glucose, vitamins, minerals are absorbed, which have remained undigested due to the large number of microorganisms in the intestines.

In the initial segment of the large intestine, an almost complete assimilation of the liquid received there (1.5-2 liters) occurs.

The microflora of the large intestine is of great importance for human health. More than 90% are bifidobacteria, about 10% are lactic acid and Escherichia coli, enterococci, etc. The composition of the microflora and its functions depend on the nature of the diet, the time of movement through the intestines and the intake of various medications.

The main functions of normal intestinal microflora:

• protective function - creating immunity;
• participation in the digestion process - the final digestion of food; synthesis of vitamins and enzymes;
• maintaining the constancy of the biochemical environment of the gastrointestinal tract.

One of the important functions of the large intestine is the formation and excretion of feces from the body.