Table 1 Main functions of the gut microbiota

Main functions

Description

Digestion

Protective functions

Synthesis of immunoglobulin A and interferons by colonocytes, phagocytic activity of monocytes, proliferation of plasma cells, formation of intestinal colonization resistance, stimulation of the development of the intestinal lymphoid apparatus in newborns, etc.

Synthetic function

Group K (participates in the synthesis of blood coagulation factors);

B 1 (catalyses the reaction of decarboxylation of keto acids, is a carrier of aldehyde groups);

В 2 (electron carrier with NADH);

B 3 (electron transfer to O 2);

B 5 (precursor of coenzyme A, involved in lipid metabolism);

В 6 (carrier of amino groups in reactions involving amino acids);

В 12 (participation in the synthesis of deoxyribose and nucleotides);

Detoxification function

including neutralization of certain types of drugs and xenobiotics: acetaminophen, nitrogen-containing substances, bilirubin, cholesterol, etc.

Regulatory

function

Regulation of the immune, endocrine and nervous systems (the latter - through the so-called " gut-brain-axis» -

It is difficult to overestimate the importance of microflora for the body. Thanks to the achievements modern science it is known that the normal intestinal microflora takes part in the breakdown of proteins, fats and carbohydrates, creates conditions for the optimal flow of digestion and absorption in the intestine, takes part in the maturation of immune system cells, which provides increased protective properties organism, etc.The two main functions normal microflora are: barrier from pathogenic agents and stimulation of the immune response:

BARRIER ACTION. The intestinal microflora has suppressive effect on the reproduction of pathogenic bacteria and thus prevents pathogenic infections.

Processattachments microorganisms to epithelial cellsIya includes complex mechanisms.Bacteria of the intestinal microbiota inhibit or reduce adherence of pathogenic agents by competitive exclusion.

For example, bacteria of the parietal (mucosal) microflora occupy certain receptors on the surface of epithelial cells. Pathogenic bacteria, which could bind to the same receptors, are eliminated from the intestine. Thus, intestinal bacteria prevent the penetration of pathogenic and opportunistic microbes into the mucous membrane.(especially propionic acid bacteria) P. freudenreichii have fairly good adhesive properties and attach very securely to the intestinal cells, creating the said protective barrier.Also, the bacteria of the permanent microflora help to maintain intestinal peristalsis and integrity of the intestinal mucosa. Yes, bactors - commensals of the large intestine during the catabolism of indigestible carbohydrates in the small intestine (the so-called dietary fiber) form short chain fatty acids (SCFA, short-chain fatty acids), such as acetate, propionate, and butyrate, which support barrier functions of the mucin layer mucus (increase the production of mucins and the protective function of the epithelium).

IMMUNE SYSTEM OF THE INTESTINE. More than 70% of immune cells are concentrated in the human intestine. main function The immune system of the intestine is to protect against the penetration of bacteria into the blood. The second function is the elimination of pathogens (pathogenic bacteria). This is provided by two mechanisms: congenital (inherited by the child from the mother, people from birth have antibodies in the blood) and acquired immunity (appears after foreign proteins enter the blood, for example, after suffering an infectious disease).

Upon contact with pathogens, the body's immune defenses are stimulated. When interacting with Toll-like receptors, synthesis is triggered various types cytokines. The intestinal microflora affects specific accumulations of lymphoid tissue. This stimulates the cellular and humoral immune response. Cells of the intestinal immune system actively produce secretory immunolobulin A (LgA) - a protein that is involved in local immunity and is the most important marker of the immune response.

ANTIBIOTIC-LIKE SUBSTANCES. Also, the intestinal microflora produces many antimicrobial substances that inhibit the reproduction and growth of pathogenic bacteria. With dysbiotic disorders in the intestine, there is not only an excessive growth of pathogenic microbes, but also a general decrease in the body's immune defenses.Normal intestinal microflora plays a particularly important role in the life of the body of newborns and children.

Thanks to the production of lysozyme, hydrogen peroxide, lactic, acetic, propionic, butyric and a number of other organic acids and metabolites that reduce the acidity (pH) of the environment, bacteria of normal microflora effectively fight pathogens. In this competitive struggle of microorganisms for survival, antibiotic-like substances such as bacteriocins and microcins occupy a leading place. Below picture Left: Colony of acidophilus bacillus (x 1100), On right: Destruction of Shigella flexneri (a) (Shigella Flexner - a type of bacteria that causes dysentery) under the action of bacteriocin-producing cells of acidophilus bacillus (x 60,000)

It should be noted that almost all microorganisms in the intestinehave a special form of coexistence called a biofilm. Biofilm iscommunity (colony)microorganisms located on any surface, the cells of which are attached to each other. Usually, cells are immersed in the extracellular polymeric substance secreted by them - mucus. It is the biofilm that performs the main barrier function from the penetration of pathogens into the blood, by eliminating the possibility of their penetration to epithelial cells.

For more information about biofilm, see:

HISTORY OF STUDYING THE COMPOSITION OF THE GIT MICROFLORA

The history of the study of the composition of the microflora of the gastrointestinal tract (GIT) began in 1681, when the Dutch researcher Anthony van Leeuwenhoek first reported his observations on bacteria and other microorganisms found in human feces and put forward a hypothesis about the coexistence of different types of bacteria in the gastrointestinal tract. -intestinal tract.

In 1850, Louis Pasteur developed the concept of functional the role of bacteria in the fermentation process, and the German physician Robert Koch continued research in this direction and created a method for isolating pure cultures, which makes it possible to identify specific bacterial strains, which is necessary to distinguish between pathogenic and beneficial microorganisms.

In 1886, one of the founders of the doctrine of intestinal infections F. Escherich first described intestinal coli (Bacterium coli communae). Ilya Ilyich Mechnikov in 1888, working at the Louis Pasteur Institute, argued that in intestines a complex of microorganisms inhabits the human body, which have an “autointoxication effect” on the body, believing that the introduction of “healthy” bacteria into the gastrointestinal tract can modify the effect intestinal microflora and counteract intoxication. The practical implementation of Mechnikov's ideas was the use of acidophilic lactobacilli for therapeutic purposes, which began in the USA in 1920-1922. Domestic researchers began to study this issue only in the 50s of the XX century.

In 1955 Peretz L.G. showed that intestinal coli of healthy people is one of the main representatives of the normal microflora and plays a positive role due to its strong antagonistic properties against pathogenic microbes. Started over 300 years ago, studies of the composition of the intestinal microbiocenosis, its normal and pathological physiology and the development of ways to positively influence the intestinal microflora continue to this day.

HUMAN AS A BACTERIA HABITAT

The main biotopes are: gastrointestinaltract(oral cavity, stomach, small intestine, large intestine), skin, respiratory tract, urogenital system. But the main interest for us here are the organs of the digestive system, because. the bulk of various microorganisms lives there.

The microflora of the gastrointestinal tract is the most representative, the mass of intestinal microflora in an adult is more than 2.5 kg, with a population of up to 10 14 CFU / g. It was previously believed that the microbiocenosis of the gastrointestinal tract includes 17 families, 45 genera, more than 500 species of microorganisms (the latest data is about 1500 species) constantly being adjusted.

Taking into account new data obtained in the study of the microflora of various biotopes of the gastrointestinal tract using molecular genetic methods and the method of gas-liquid chromatography-mass spectrometry, the total genome of bacteria in the gastrointestinal tract has 400 thousand genes, which is 12 times the size of the human genome.

exposed analysis on the homology of the sequenced 16S pRNA genes of the parietal (mucosal) microflora of 400 different sections of the gastrointestinal tract, obtained by endoscopy various sections of the intestines of volunteers.

As a result of the study, it was shown that the parietal and luminal microflora includes 395 phylogenetically isolated groups of microorganisms, of which 244 are absolutely new. At the same time, 80% of the new taxa identified in the molecular genetic study belong to non-cultivated microorganisms. Most of the proposed new phylotypes of microorganisms are representatives of the genera Firmicutes and Bacteroides. The total number of species is close to 1500 and requires further clarification.

The gastrointestinal tract communicates with the gastrointestinal tract through a system of sphincters. external environment the world around us and at the same time through the intestinal wall - with the internal environment of the body. Due to this feature, the gastrointestinal tract has created its own environment, which can be divided into two separate niches: chyme and mucous membrane. The human digestive system interacts with various bacteria, which can be referred to as "endotrophic microflora of the human intestinal biotope". Human endotrophic microflora is divided into three main groups. The first group includes useful for humans eubiotic indigenous or eubiotic transient microflora; to the second - neutral microorganisms, constantly or periodically sown from the intestine, but not affecting human life; to the third - pathogenic or potentially pathogenic bacteria ("aggressive populations").

Cavity and wall microbiotopes of the gastrointestinal tract

In microecological terms, the gastrointestinal biotope can be divided into tiers (oral cavity, stomach, intestines) and microbiotopes (cavitary, parietal and epithelial).

The ability to apply in the parietal microbiotope, i.e. histadhesiveness (the ability to fix and colonize tissues) determines the essence of transient or indigenous bacteria. These signs, as well as belonging to a eubiotic or aggressive group, are the main criteria characterizing a microorganism interacting with the gastrointestinal tract. Eubiotic bacteria are involved in the creation of colonization resistance of the organism, which is a unique mechanism of the system of anti-infective barriers.

Cavitary microbiotope throughout the gastrointestinal tract is heterogeneous, its properties are determined by the composition and quality of the contents of a particular tier. Tiers have their own anatomical and functional features, so their content differs in the composition of substances, consistency, pH, speed of movement and other properties. These properties determine the qualitative and quantitative composition of cavity microbial populations adapted to them.

Parietal microbiotope is the most important structure, limiting the internal environment of the body from the external. It is represented by mucous overlays (mucous gel, mucin gel), glycocalyx located above the apical membrane of enterocytes and the surface of the apical membrane itself.

The parietal microbiotope is of the greatest (!) interest from the point of view of bacteriology, since it is in it that interaction with bacteria that is beneficial or harmful to humans occurs - what we call symbiosis.

It should be noted that in the intestinal microflora there are 2 types:

• mucosal (M) flora- mucosal microflora interacts with the mucous membrane of the gastrointestinal tract, forming a microbial-tissue complex - microcolonies of bacteria and their metabolites, epithelial cells, goblet cell mucin, fibroblasts, immune cells of Peyer's plaques, phagocytes, leukocytes, lymphocytes, neuroendocrine cells;
• translucent (P) flora- luminal microflora is located in the lumen of the gastrointestinal tract, does not interact with the mucous membrane. The substrate for its life is indigestible dietary fiber, on which it is fixed.

To date, it is known that the microflora of the intestinal mucosa differs significantly from the microflora of the intestinal lumen and feces. Although each adult has a specific combination of predominant bacterial species in the gut, the composition of the microflora can change with lifestyle, diet, and age. A comparative study of the microflora in adults who are genetically related to one degree or another revealed that genetic factors influence the composition of the intestinal microflora more than nutrition.

Figure Note: FOG - fundus of the stomach, AOG - antrum of the stomach, duodenum - duodenum (:Chernin V.V., Bondarenko V.M., Parfenov A.I. Participation of the luminal and mucosal microbiota of the human intestine in symbiotic digestion. Bulletin of the Orenburg Scientific Center of the Ural Branch of the Russian Academy of Sciences ( electronic journal), 2013, №4)

The location of the mucosal microflora corresponds to the degree of its anaerobiosis: obligate anaerobes (bifidobacteria, bacteroids, propionic acid bacteria, etc.) occupy a niche in direct contact with the epithelium, followed by aerotolerant anaerobes (lactobacilli, etc.), even higher - facultative anaerobes, and then - aerobes .Translucent microflora is the most variable and sensitive to various exogenous influences. Changes in diets, environmental impacts, drug therapy, primarily affect the quality of the translucent microflora.

See additionally:

The number of microorganisms of mucosal and luminal microflora

The mucosal microflora is more resistant to external influences than the luminal microflora. The relationship between mucosal and luminal microflora is dynamic and determined by the following factors:

• endogenous factors - the influence of the mucous membrane of the digestive canal, its secrets, motility and the microorganisms themselves;
  
• exogenous factors - influence directly and indirectly through endogenous factors, for example, the intake of a particular food changes the secretory and motor activity of the digestive tract, which transforms its microflora
  

MICROFLORA OF THE MOUTH, ESOPHAGUS AND STOMACH

Consider the composition of the normal microflora of different parts of the gastrointestinal tract.

The oral cavity and pharynx carry out preliminary mechanical and chemical processing of food and assess the bacteriological hazard with respect to penetrating substances. human body bacteria.

Saliva is the first digestive fluid that processes food substances and affects the penetrating microflora. General content bacteria in saliva is variable and averages 108 MK/ml.

As part of the normal microflora oral cavity includes streptococci, staphylococci, lactobacilli, corynebacteria, a large number of anaerobes. In total, the microflora of the mouth has more than 200 species of microorganisms.

On the surface of the mucosa, depending on the individual used hygiene products found about 10 3 -10 5 MK/mm2. The colonization resistance of the mouth is carried out mainly by streptococci (S. salivarus, S. mitis, S. mutans, S. sangius, S. viridans), as well as representatives of the skin and intestinal biotopes. At the same time, S. salivarus, S. sangius, S. viridans adhere well to the mucous membrane and dental plaque. These alpha-hemolytic streptococci, which have a high degree histadgesia, inhibit the colonization of the mouth by fungi of the genus Candida and staphylococci.

The microflora transiently passing through the esophagus is unstable, does not show histadhesiveness to its walls and is characterized by an abundance of temporarily located species that enter from the oral cavity and pharynx. In the stomach, relatively unfavorable conditions for bacteria are created due to hyperacidity, exposure to proteolytic enzymes, rapid motor-evacuation function of the stomach and other factors that limit their growth and reproduction. Here, microorganisms are contained in an amount not exceeding 10 2 -10 4 per 1 ml of content.Eubiotics in the stomach master mainly the cavity biotope, the parietal microbiotope is less accessible to them.

The main microorganisms active in the gastric environment are acid resistant representatives of the genus Lactobacillus with or without a histadhesive relationship to mucin, some types of soil bacteria and bifidobacteria. Lactobacilli, despite the short residence time in the stomach, are capable, in addition to their antibiotic action in the stomach cavity, to temporarily colonize the parietal microbiotope. As a result of the joint action of protective components, the bulk of microorganisms that have entered the stomach die. However, in case of malfunction of the mucous and immunobiological components, some bacteria find their biotope in the stomach. So, due to pathogenicity factors, the population of Helicobacter pylori is fixed in the gastric cavity.

A little about the acidity of the stomach: The maximum theoretically possible acidity in the stomach is 0.86 pH. The minimum theoretically possible acidity in the stomach is 8.3 pH. Normal acidity in the lumen of the body of the stomach on an empty stomach is 1.5-2.0 pH. The acidity on the surface of the epithelial layer facing the lumen of the stomach is 1.5-2.0 pH. Acidity in the depth of the epithelial layer of the stomach is about 7.0 pH.

MAIN FUNCTIONS OF THE SMALL INTESTINE

Small intestine - This is a tube about 6m long. It occupies almost the entire lower part abdominal cavity and is the longest part of the digestive system, connecting the stomach to the large intestine. Most of the food is already digested in small intestine with the help of special substances - enzymes (enzymes).

To the main functions of the small intestine include cavity and parietal hydrolysis of food, absorption, secretion, as well as barrier-protective. In the latter, in addition to chemical, enzymatic and mechanical factors, the indigenous microflora of the small intestine plays a significant role. She takes an active part in the cavity and parietal hydrolysis, as well as in the absorption of nutrients. The small intestine is one of the most important links that ensure the long-term preservation of the eubiotic parietal microflora.

There is a difference in the colonization of cavitary and parietal microbiotopes with eubiotic microflora, as well as in the colonization of tiers along the length of the intestine. The cavity microbiotope is subject to fluctuations in the composition and concentration of microbial populations; the wall microbiotope has a relatively stable homeostasis. In the thickness of the mucous overlays, populations with histadhesive properties to mucin are preserved.

The proximal small intestine normally contains a relatively small amount of gram-positive flora, consisting mainly of lactobacilli, streptococci and fungi. The concentration of microorganisms is 10 2 -10 4 per 1 ml of intestinal contents. As we approach the distal parts of the small intestine, the total number of bacteria increases to 10 8 per 1 ml of content, at the same time additional species appear, including enterobacteria, bacteroids, bifidobacteria.

MAIN FUNCTIONS OF THE LARGE INTESTINE

The main functions of the large intestine are reservation and evacuation of chyme, residual digestion of food, excretion and absorption of water, absorption of some metabolites, residual nutrient substrate, electrolytes and gases, formation and detoxification of feces, regulation of their excretion, maintenance of barrier-protective mechanisms.

All of these functions are performed with the participation of intestinal eubiotic microorganisms. The number of microorganisms in the colon is 10 10 -10 12 CFU per 1 ml of content. Bacteria account for up to 60% of stool. Throughout life, a healthy person is dominated by anaerobic species of bacteria (90-95% of the total composition): bifidobacteria, bacteroids, lactobacilli, fusobacteria, eubacteria, veillonella, peptostreptococci, clostridia. From 5 to 10% of the microflora of the colon are aerobic microorganisms: Escherichia, Enterococcus, Staphylococcus, different kinds opportunistic enterobacteria (Proteus, Enterobacter, Citrobacter, Serrations, etc.), non-fermenting bacteria (pseudomonas, Acinetobacter), yeast-like fungi of the genus Candida, etc.

Analyzing the species composition of the colon microbiota, it should be emphasized that, in addition to the indicated anaerobic and aerobic microorganisms, its composition includes representatives of nonpathogenic protozoan genera and about 10 intestinal viruses.Thus, in healthy individuals, there are about 500 types of various microorganisms in the intestines, most of which are representatives of the so-called obligate microflora - bifidobacteria, lactobacilli, non-pathogenic coli and others. 92-95% of the intestinal microflora consists of obligate anaerobes.

1. Predominant bacteria. Due to anaerobic conditions in a healthy person, anaerobic bacteria predominate (about 97%) in the composition of the normal microflora in the large intestine:bacteroids (especially Bacteroides fragilis), anaerobic lactic acid bacteria (eg Bifidumbacterium), clostridia (Clostridium perfringens), anaerobic streptococci, fusobacteria, eubacteria, veillonella.

2. Small part microflora make up aerobic andfacultative anaerobic microorganisms: gram-negative coliform bacteria (primarily Escherichia coli - E.Coli), enterococci.

3. In a very small amount: Staphylococci, Proteus, Pseudomonas, fungi of the genus Candida, certain types of spirochetes, mycobacteria, mycoplasmas, protozoa and viruses

Qualitative and quantitative COMPOUND the basic microflora of the large intestine in healthy people (CFU/g faeces) varies depending on their age group.

On the image features of the growth and enzymatic activity of bacteria in the proximal and distal parts of the large intestine are shown under various conditions of molarity, mM (molar concentration) of short-chain fatty acids (SCFA) and the pH value, pH (acidity) of the medium.

« number of storeys resettlement bacteria»

For a better understanding of the topic, we will give a brief definition.understanding the concepts of what aerobes and anaerobes are

Anaerobes- organisms (including microorganisms) that receive energy in the absence of oxygen access by substrate phosphorylation, the end products of incomplete oxidation of the substrate can be oxidized with more energy in the form of ATP in the presence of the final proton acceptor by organisms that carry out oxidative phosphorylation.

Facultative (conditional) anaerobes- organisms whose energy cycles follow the anaerobic path, but are able to exist even with the access of oxygen (that is, they grow both in anaerobic and aerobic conditions), in contrast to obligate anaerobes, for which oxygen is detrimental.

Obligate (strict) anaerobes- organisms that live and grow only in the absence of molecular oxygen in the environment, it is detrimental to them.

The role of colon bacteria living in close symbiosis with the human body is invaluable. These microorganisms are of great importance. The microflora of the large intestine is involved in the process of digestion of food, prevents the development of putrefactive processes, fights infection and improves immunity. The destruction of intestinal bacteria can lead to a number of problems, at first glance, have nothing to do with digestion. Normal microflora is, without exaggeration, good health and longevity.

Peculiarities

The microorganisms that live in the large intestine are closely related to each other. The large intestine has 17 families, 45 genera and at least 500 species of stable microflora. If it is easier to approach the classification of intestinal bacteria, they are conditionally divided into 3 groups:

• home;
• concomitant;
• residual.

The main group is bifidobacteria and bacteroids. They have the largest part of the composition (about 90%). The associated microflora includes lactobacilli, escherichia and enterococci. They make up 9%. Residual - citrobacter, enterobacter, yeast, staphylococcus - do not matter much. They are the least. The lower colon is characterized by a large number of such bacteria, especially in comparison with other parts of the digestive tract. Normal microflora takes over the formation of the reaction of the immune system. This is done by a little inflammation. The vital activity of bacteria ends with the formation of organic acids, from which pathogenic microorganisms do not multiply. Bacteria synthesize a number of vitamins that have a positive effect on the mucosa, participate in the decomposition of proteins and water (hydrolysis). In this way, bacteria participate in the process of digestion of food.

Functions of bacteria in the human large intestine

Every function of the colon is not complete without bifidobacteria. In combination with lactobacilli, eubacteria, propionbacteria and bacteroids, they are necessary for protein hydrolysis and carbohydrate fermentation. The same microorganisms that live in the mucosa in the colon, decompose coarse fiber and increase peristalsis. Escherichia, thanks to the secreted enzymes, synthesize vitamins and essential acids. Bifido- and lactobacilli stimulate the lymph circulation in the intestines, participate in the formation of immunoglobulins and produce interferon, a substance that helps fight infection. Anaerobic microorganisms contribute by producing a substance that affects the digestive and cardiovascular systems, as well as the hematopoietic system.

The qualitative and quantitative composition of the microflora is influenced by many external and internal factors. Vegetarians have more enterococci and eubacteria. Predominance in the nutrition of plant foods contributes to the reproduction of this group of bacteria. Those who often eat meat and animal fats multiply clostridia and bacteroids. At the same time, the number of bifidobacteria and enterococci decreases. To create the conditions that are necessary for the reproduction of bifidobacteria, milk and dairy products play an important role. The microflora is regulated in a natural way, thanks to antimicrobial substances that are synthesized by the colon mucosa. No wonder experts put proper nutrition in the first place. Even the slightest imbalance of the necessary bacteria (destruction of some and an increase in the number of others) can lead to unpleasant consequences - dysbacteriosis.

Dysbacteriosis

Violations of the quantitative values ​​of the bacteria that make up the microflora is called dysbacteriosis. Significantly reduced bifidobacteria and lactobacilli. Dysbacteriosis of the large intestine does not occur from scratch. The cause may be a congenital pathology, surgical intervention long-term use of antibiotics. The antibiotic is especially dangerous. Its action is based on the destruction of certain types of intestinal bacteria and stimulation of the growth of pathogenic microflora with opportunistic pathogens. It must be remembered that the latter is present in the intestine, but its reproduction is inhibited by normal microflora. Diseases of the colon. Do not self-diagnose and do not start treatment intestinal disorders on the advice of friends and acquaintances. To diagnose dysbacteriosis, it is usually enough to sow feces on the microflora. Sometimes other specific tests are used - breath tests with carbon or with glucose and hydrogen.

The human large intestine, unlike other parts of the digestive tract, is abundantly populated by microorganisms. The content of microbes in the colon is 10 11 -10 12 per 1 ml of content. About 90% of the microflora of the colon is obligate anaerobic bifidobacteria And bacteroids. Lactic acid bacteria, Escherichia coli, streptococci are found in smaller numbers. Colon microorganisms perform a number of important functions. Enzymes produced by bacteria can partially break down plant fibers that are not digested in the overlying sections of the digestive tract - cellulose, pectins, lignins. The microflora of the colon synthesizes vitamins K and group B(B 1, B 6, B 12), which can be absorbed in the large intestine in small quantities. Microorganisms are also involved in enzyme inactivation digestive juices. The most important function of the colon microflora is the ability to protect the body from pathogenic bacteria entering the digestive tract. Normal microflora prevents reproduction in the intestine pathogenic microorganisms and their entry into the internal environment of the body. Violation of the normal composition of the microflora of the colon with long-term use antibacterial drugs accompanied by active reproduction of pathogenic microbes and leads to a decrease in the body's immune defenses.

defecation. defecation(colon emptying) is a strictly coordinated reflex act, which is carried out as a result of coordinated motor activity of the muscles of the final sections of the large intestine and its sphincters and includes involuntary and arbitrary components. Non-arbitrary component defecation consists in peristaltic contraction of the smooth muscles of the wall of the distal colon (descending colon, sigmoid and rectum) and relaxation of the internal anal sphincter. This process is initiated stretching fecal masses of the walls of the rectum and is carried out with the help of local reflexes that close in the neurons of the intestinal wall, as well as spinal reflexes that close in the neurons of the sacral region spinal cord(S 2- S 4), where is located spinal defecation center. Efferent nerve impulses from this center along the parasympathetic fibers of the pelvic and pudendal nerves cause relaxation of the internal anal sphincter and increased rectal motility.

The urge to defecate occurs when the rectum is filled to 25% of its volume. However, in the absence of conditions, after some time, the rectum stretched with fecal masses adapts to an increased volume, the smooth muscles of the intestinal wall relax and the internal anal sphincter contracts. At the same time, the external anal sphincter, formed by striated muscles, remains in a state of tonic contraction. If there are appropriate conditions for defecation, an arbitrary component joins the involuntary component, which consists in relaxing the external anal sphincter, contracting the diaphragm and abdominal muscles which increases intra-abdominal pressure. To turn on an arbitrary component of defecation, it is necessary to excite centers medulla oblongata, hypothalamus and cortex hemispheres. If the sacral spinal cord is damaged, the defecation reflex disappears completely. In case of spinal cord injury, sacral departments the involuntary component of the reflex is preserved, but the ability to arbitrary act defecation.

6. SUCTION - this is the process of transferring nutrients, water, ions, vitamins, microelements from the lumen of the digestive tract into the blood and lymph.

Nutrients are absorbed in the form of monomers formed during the digestion of food in the gastrointestinal tract. Active and complete absorption occurs with the formation of a sufficient amount of monomers in the process of splitting nutrients, good blood supply to the mucous membrane of the digestive tract, and subject to the full functional activity of the cells of the mucous membrane, through which monomers of nutrients are transported into the internal environment of the body. A small amount of water and ions is absorbed through the intercellular spaces.

IN various departments digestive tract absorption is carried out with different intensity. In the oral cavity, nutrients are practically not absorbed due to the short stay of food. However, some drugs (validol, nitroglycerin) when they are in the oral cavity (“resorption”) quickly enter the bloodstream due to the abundant blood supply to its mucosa. Water, ions, glucose, alcohol, a small amount of amino acids are absorbed in the stomach. The most active absorption processes occur in the small intestine, the surface area of ​​which increases significantly due to the circular folds of the mucosa and intestinal villi and microvilli. Intestinal villi have a dense network of capillaries characterized by high permeability. The rhythmic contraction of the villi contributes to a better contact of their surface with the contents of the intestine and facilitates the outflow of blood and lymph with absorbed monomers due to compression of the blood and lymphatic vessels. The large intestine mainly absorbs water. In the rectum, glucose, amino acids, and vitamins can be absorbed in small amounts, which is used for medicinal purposes when prescribing nutritional enemas.

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1 Structure and function of the large intestine. Importance of intestinal microflora. Influence of nutritional factors on the large intestine

The structure and functions of the large intestine

The large intestine is the last section of the gastrointestinal tract and consists of six sections:

The caecum (cecum, cecum) with an appendix (vermiform appendix);

ascending colon;

Transverse colon;

descending colon;

Sigmoid colon;

Rectum.

The total length of the large intestine is 1-2 meters, the diameter in the region of the caecum is 7 cm and gradually decreases towards the ascending colon to 4 cm. Distinctive features large intestine compared to the small intestine are:

The presence of three special longitudinal muscle cords or ribbons that begin near the appendix and end at the beginning of the rectum; they are located at an equal distance from each other (in diameter);

The presence of characteristic swellings, which look like protrusions on the outside, and bag-shaped depressions on the inside;

The presence of processes of the serous membrane 4-5 cm long, which contain adipose tissue.

The cells of the mucous membrane of the colon do not have villi, since the intensity of absorption processes in it is significantly reduced.

In the large intestine, water absorption ends and feces are formed. Mucus is secreted by the cells of the mucous membrane for their formation and movement through the sections of the large intestine.

In the lumen of the colon, a large number of microorganisms live, with which the human body normally establishes symbiosis. On the one hand, microbes absorb food residues and synthesize vitamins, a number of enzymes, amino acids and other compounds. At the same time, a change in the quantitative and especially qualitative composition of microorganisms leads to significant violations functional activity organism as a whole. This can happen when the rules of nutrition are violated - the consumption of large quantities of refined foods with a low content of dietary fiber, excess food, etc.

Under these conditions, the so-called putrefactive bacteria begin to predominate, releasing substances in the process of vital activity that have Negative influence per person. This condition is defined as intestinal dysbiosis. We will talk about it in detail in the section on the colon.

Fecal (fecal) masses move through the intestines due to wave-like movements colon(peristalsis) and reach the rectum - the last section, which serves for their accumulation and excretion. In its lowest section there are two sphincters - internal and external, which close anus and open during bowel movements. The opening of these sphincters is normally regulated by the central nervous system. The urge to defecate in a person appears with mechanical irritation of the receptors of the anus.

Importance of intestinal microflora

The human gastrointestinal tract is inhabited by numerous microorganisms, the metabolism of which is closely integrated into the metabolism of the macroorganism. Microorganisms inhabit all parts of the gastrointestinal tract, but in the most significant quantities and diversity are presented in the large intestine.

The most important and studied functions of the intestinal microflora are the provision of anti-infective protection, stimulation of the immune functions of the macroorganism, nutrition of the colon, absorption of minerals and water, synthesis of B and K vitamins, regulation of lipid and nitrogen metabolism, regulation of intestinal motility.

Anti-infective protection performed by intestinal microorganisms is largely associated with the antagonism of representatives of the normal microflora in relation to other microbes. The suppression of the activity of some bacteria by others is carried out in several ways. These include competition for substrates for growth, competition for fixation sites, induction of an immune response of a macroorganism, stimulation of peristalsis, creation of an unfavorable environment, modification/deconjugation of bile acids (as one of the ways to modify environmental conditions), and synthesis of antibiotic-like substances.

The metabolic effects of the normal intestinal microflora associated with the synthesis of short chain fatty acids (SCFA) have been well studied. The latter are formed as a result of anaerobic fermentation of di-, oligo- and polysaccharides available to bacteria. Locally, SCFA determine the decrease in pH and provide colonization resistance, and also take part in the regulation of intestinal motility. The formation of butyrate is extremely important for the epithelium of the colon, because. it is butyrate that colonocytes use to meet their energy needs. In addition, butyrate is a regulator of apoptosis, differentiation and proliferation processes, and therefore anticarcinogenic effects are associated with it. Finally, butyrate is directly involved in the absorption of water, sodium, chlorine, calcium and magnesium. Therefore, its formation is necessary to maintain the water and electrolyte balance in the body, as well as to provide the macroorganism with calcium and magnesium.

In addition, the decrease in pH associated with the formation of SCFAs leads to the fact that ammonia, which is formed in the colon in connection with the microbial metabolism of proteins and amino acids, passes into ammonium ions and in this form cannot freely diffuse through the intestinal wall into the blood, but excreted in the feces in the form of ammonium salts.

Another important function of the microflora is to convert bilirubin to urobilinogen, which is partly absorbed and excreted in the urine and partly excreted in the feces.

Finally, the participation of the colon microflora in lipid metabolism seems to be extremely important. Microbes metabolize cholesterol that enters the large intestine into coprostanol and then into coprostanone. Acetate and propionate formed as a result of fermentation, having been absorbed into the bloodstream and reaching the liver, can affect the synthesis of cholesterol. In particular, it has been shown that acetate stimulates its synthesis, while propionate inhibits it. The third way of influence of microflora on lipid metabolism in the macroorganism is associated with the ability of bacteria to metabolize bile acids, in particular, cholic acid. Unabsorbed in the distal regions ileum conjugated cholic acid in the colon undergoes deconjugation by microbial choleglycine hydrolase and dehydroxylation with the participation of 7-alpha-dehydroxylase. This process is stimulated by an increase in the pH values ​​in the intestine. The resulting deoxycholic acid binds to dietary fiber and is excreted from the body. With an increase in pH, deoxycholic acid is ionized and well absorbed in the large intestine, and when it decreases, it is excreted. The absorption of deoxycholic acid provides not only replenishment of the pool of bile acids in the body, but is also an important factor stimulating the synthesis of cholesterol. An increase in pH values ​​in the colon, which may be associated with various reasons, leads to an increase in the activity of enzymes leading to the synthesis of deoxycholic acid, to an increase in its solubility and absorption and, as a result, an increase in the blood level of bile acids, cholesterol and triglycerides. One of the reasons for the increase in pH may be the lack of prebiotic components in the diet, which disrupt the growth of normal microflora, incl. bifido- and lactobacilli.

Another important metabolic function of the intestinal microflora is the synthesis of vitamins. In particular, B vitamins and vitamin K are synthesized. The latter is necessary in the body for the so-called. calcium-binding proteins that ensure the functioning of the blood coagulation system, neuromuscular transmission, bone structure, etc. Vitamin K is a complex of chemical compounds, among which are vitamin K1 - phylloquinone - of plant origin, as well as vitamin K2 - a group of compounds called menaquinones - synthesized microflora in the small intestine. The synthesis of menaquinones is stimulated with a lack of phyloquinone in the diet and may increase with excessive growth of the small intestine microflora, for example, while taking drugs that reduce gastric secretion. Conversely, the use of antibiotics, leading to the suppression of the small intestine microflora, can lead to the development of antibiotic-induced hemorrhagic diathesis(hypoprothrombinemia).

The fulfillment of the listed and many other metabolic functions is possible only if the normal microflora is fully provided with the nutrients necessary for its growth and development. The most important energy sources for it are carbohydrates: di-, oligo- and polysaccharides that do not break down in the lumen of the small intestine, which are called prebiotics. The microflora receives nitrogenous components for its growth to a large extent during the breakdown of mucin, a component of mucus in the large intestine. The resulting ammonia should be eliminated under conditions of low pH values, which is ensured by short-chain fatty acids formed as a result of the metabolism of prebiotics. The detoxifying effect of non-digestible disaccharides (lactulose) is well known and has long been used in clinical practice. For normal life, colon bacteria also need vitamins, some of which they synthesize themselves. At the same time, part of the synthesized vitamins is absorbed and used by the macroorganism, but the situation is different with some of them. For example, a number of bacteria living in the colon, in particular, representatives of Enterobacteriacea, Pseudomonas, Klebsiella, can synthesize vitamin B12, but this vitamin cannot be absorbed in the colon and is inaccessible to the macroorganism.

In this regard, the nature of the child's nutrition to a large extent determines the degree of integration of microflora into his own metabolism. This is especially pronounced in children of the first year of life who are breastfed or artificially fed. The intake of prebiotics (lactose and oligosaccharides) with human milk contributes to the successful development of the normal intestinal microflora of a newborn child with a predominance of bifido- and lactoflora, while with artificial feeding with formulas based on cow's milk without prebiotics, streptococci, bacteroids, representatives of Enterobacteriacea are predominant. Accordingly, the spectrum of bacterial metabolites in the intestine and the nature of metabolic processes also change. So, the predominant SCFAs with natural feeding are acetate and lactate, and with artificial feeding - acetate and propionate. Protein metabolites (phenols, cresol, ammonia) are formed in large quantities in the intestines of formula-fed children, and their detoxification, on the contrary, is reduced. Also, the activity of beta-glucuronidase and beta-glucosidase is higher (typical for Bacteroides and Closridium). The result of this is not only a decrease in metabolic functions, but also a direct damaging effect on the intestines.

In addition, there is a certain sequence of formation of metabolic functions, which should be taken into account when determining the diet of a child in the first year of life. So normally, the breakdown of mucin is determined after 3 months. life and is formed by the end of the first year, deconjugation of bile acids - from the 1st month. life, the synthesis of coprostanol - in the 2nd half of the year, the synthesis of urobilinogen - in 11-21 months. The activity of beta-glucuronidase and beta-glucosidase in the normal development of intestinal microbiocenosis in the first year remains low.

Thus, the intestinal microflora performs numerous functions that are vital for the macroorganism. The formation of a normal microbiocenosis is inextricably linked with rational nutrition intestinal bacteria. An important component nutrition are prebiotics, which are part of human milk or as part of mixtures for artificial feeding.

Influence of nutritional factors on the large intestine

The most important irritants of the colon are dietary fiber, B vitamins, especially thiamine. A laxative effect when taken in sufficient doses is provided by sources of high concentrations of sugar, honey, beetroot puree, carrots, dried fruits (especially plums), xylitol, sorbitol, mineral water rich in magnesium salts, sulfates (such as Batalineka). Violations of the motor and excretory functions of the large intestine develop with the predominant consumption of refined and other foods devoid of dietary fiber (white bread, pasta, rice, semolina, eggs, etc.), as well as with a lack of vitamins, especially group B.

The delay in the release of decay products (constipation) causes an increase in the intake toxic substances to the liver, which aggravates its function, leads to the development of atherosclerosis, other diseases, to early aging. Overloading the diet with meat products increases the processes of decay. So, indole is formed from tryptophan, it contributes to the manifestation of the action of some chemical carcinogens. To suppress the activity of putrefactive microflora in the large intestine, II Mechnikov considered it expedient to consume lactic acid products.

An excess of carbohydrates in the diet causes the development of fermentation processes.

Thus, the final section of the digestive tract is involved in the excretion of toxins from the body, and also performs a number of other functions. With the help of nutrition, it is possible to influence the activity of the large intestine and the microflora inhabiting it.

The concept of the coefficient of assimilation. Comparing the composition of food and excrement excreted through the large intestine, it is possible to determine the degree of absorption of nutrients by the body. So, to determine the digestibility of this type of protein, the amount of nitrogen in food and feces is compared. As you know, proteins are the main source of nitrogen in the body. On average, despite the diversity of these substances in nature, they contain about 16% nitrogen (hence, 1 g of nitrogen corresponds to 6.25 g of protein). The absorption coefficient is equal to the difference between the amounts of nitrogen in consumed products and feces, expressed as a percentage; it corresponds to the proportion of protein retained in the body. Example: the diet contained 90 g of protein, which corresponds to 14.4 g of nitrogen; 2 g of nitrogen was excreted with excrement. Consequently, 12.4 g of nitrogen was retained in the body, which corresponds to 77.5 g of protein, i.e. 86% of the administered with food.

Nutrient digestibility is influenced by many factors: food composition, including the amount of ballast compounds, technological processing of products, their combination, the functional state of the digestive apparatus, etc. Digestibility deteriorates with age. This must be taken into account when selecting products and methods of their technological processing for the diets of the elderly. The degree of digestibility is affected by the volume of food, so it is necessary to distribute the mass of food into several meals during the day, taking into account living conditions and health status.

Bacterial intestinal flora in healthy children of different ages, its physiological role. The concept of eubiosis and dysbacteriosis

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Bacterial preparations used for the prevention of dysbacteriosis and treatment intestinal diseases in children

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The influence of harmful factors on the fetus

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Restorative correction of the functional reserves of the organism of students in the university complex

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In a healthy child, from the moment of birth, there is a rapid colonization of the intestine by bacteria that are part of the intestinal and vaginal flora of the mother. Bacteria can be found in the cavities of the gastrointestinal tract a few hours after birth ...

Intestinal dysbiosis and chronic infections: urogenital, etc.

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Normoflora (cultivation, preparations)

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Features of care for patients with diseases of the gastrointestinal tract

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Physiology of Nutrition

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Microflora of the large intestine. The role of the microflora of the large intestine in the process of digestion and the formation of the immunological reactivity of the body.

Colon is a habitat a large number microorganisms. They form an endoecological microbial biocenosis (community). The microflora of the large intestine consists of three groups of microorganisms: the main ( bifidobacteria And bacteroids- almost 90% of all microbes), concomitant ( lactobacilli, Escherechia, enterococci- about 10%) and residual ( citrobacter, enterobacter, proteas, yeast, clostridia, staphylococci, etc. - about 1%). In the large intestine is maximum amount microorganisms (compared to other parts of the digestive tract). There are 1010-1013 microorganisms per 1 g of feces.

Normal microflora of a healthy person participates in the formation of the immunological reactivity of the human body, prevents the development of pathogenic microbes in the intestines, synthesizes vitamins (folic acid, cyanocobalamin, phylloquinones) and physiologically active amines, hydrolyzes toxic metabolic products of proteins, fats and carbohydrates, preventing endotoxemia (Fig. 11.16) .

In the process of life microorganisms relating to normal microflora, organic acids are formed, which reduce the pH of the medium and thereby prevent the reproduction of pathogenic, putrefactive and gas-forming microorganisms.

bifidobacteria, lactobacilli, eubacteria, propionbacteria And bacteroids enhance the hydrolysis of proteins, ferment carbohydrates, saponify fats, dissolve fiber and stimulate intestinal motility. Bifido- and eubacteria, as well as Escherichia due to their enzyme systems, they participate in the synthesis and absorption of vitamins, as well as essential amino acids. Bacterial modulins bifido- And lactobacilli stimulate the intestinal lymphoid apparatus, increase the synthesis of immunoglobulins, interferon and cytokines, inhibiting the development of pathogenic microbes. In addition, modulins enhance the activity of lysozyme. Anaerobic bacteria produce biologically active substances (beta-alanine, 5-aminovaleric and gamma-aminobutyric acids), mediators that affect the functions of the digestive and cardiovascular systems, as well as the hematopoietic organs.

per composition microbial community of the large intestine influenced by many endogenous and exogenous factors. Thus, plant foods increase enterococci And eubacteria, animal proteins and fats promote reproduction clostridia And bacteroids, but reduce the amount bifidobacteria And enterococci, dairy food leads to an increase in the number bifidobacteria.

The natural regulator of the intestinal microflora are antimicrobial agents produced by the intestinal mucosa and contained in digestive secrets (lysozyme, lactoferrin, defenins, secretory immunoglobulin A). Normal intestinal peristalsis, which moves the chyme in the distal direction, has a great influence on the level of microbial population of each section of the intestinal tract, preventing their spread in the proximal direction. Therefore, violations of the motor activity of the intestine contribute to the occurrence of dysbacteriosis (changes in the quantitative ratios and composition of the microflora).