The main role of the microflora of the large intestine is to. Causes of changes in the normal intestinal microflora. Disorders of the human intestinal microflora

From the small intestine, food enters the large intestine. The mucous membrane of the large intestine forms crescent-shaped folds, there are no villi on it. Colon is a continuation of the ileum and is the final section of the gastrointestinal tract. The length of the large intestine is 1–1.65 m. The formation of feces occurs in the large intestine. In the large intestine, there are: the cecum with the appendix, the colon, consisting of the ascending, transverse, descending, sigmoid colons and the rectum, which ends with the anus.

Distinctive features of the large intestine are the presence of longitudinal muscle bands (mesenteric, omental and free), swellings and omental processes.

Cecum is the initial, extended section of the large intestine. A valve is formed at the confluence of the ileum with the large intestine, which prevents the contents of the large intestine from passing into the small intestine. On the lower surface of the caecum, where the muscle bands converge colon, the vermiform appendix (appendix) begins, the length of which ranges from 2 to 20 cm, the diameter is 0.5 - 1 cm. ascending Colon, which is located in the right half of the abdomen up to the liver and passes into the transverse colon, which in turn passes into the descending colon, then into the sigmoid colon.

AT sigmoid colon towards the rectum, the protrusions gradually disappear, the muscle bands pass into a uniform layer of longitudinal muscle fibers, and at the level of the pelvic cape, it passes into the rectum. The rectum ends with the anal (anal) opening, which closes the anal sphincter. In the large intestine, the final absorption of the necessary nutrients, the release of metabolites and salts of heavy metals, the accumulation of dehydrated intestinal contents and its removal from the body take place. It is in the large intestine that the main volume of water is absorbed (5-7 liters per day). The outer muscle layer in the large intestine is located in the form of strips, between which there are swellings (food masses are retained in them, which provides a longer contact with the wall and accelerates the absorption of water). The motility of the colon increases during eating, the passage of food through the esophagus, stomach, duodenum. Inhibitory influences are carried out from the rectum, the irritation of the receptors of which reduces the motor activity of the colon. Eating rich food dietary fiber(cellulose, pectin, lignin), increases the amount of feces and accelerates its movement through the intestines

The microflora of the colon. The last sections of the large intestine contain many microorganisms, primarily bacilli of the genus Bifidus and Bacteroides. They are involved in the destruction of enzymes that come with chyme from the small intestine, the synthesis of vitamins, the metabolism of proteins, phospholipids, fatty acids, and cholesterol. The protective function is that the intestinal microflora in the host organism acts as a constant stimulus for the development of natural immunity. In addition, normal intestinal bacteria act as antagonists in relation to pathogenic microbes and inhibit their reproduction. The activity of the intestinal microflora can be disrupted after prolonged use of antibiotics, resulting in the development of yeast and fungi. Intestinal microbes synthesize vitamins K, B12, E, B6, as well as other biologically active substances, support fermentation processes and reduce decay processes.

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1 Structure and function of the large intestine. Meaning intestinal microflora. The influence of nutritional factors on colon

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);

Availability characteristic swellings, which outside have the appearance of protrusions, and from the inside - bag-shaped depressions;

The presence of processes 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 stool. Mucus is secreted by the cells of the mucous membrane for their formation and movement through the sections of the large intestine.

Lives in the lumen of the large intestine a large number of microorganisms 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 quality composition microorganisms leads to significant damage functional activity organism as a whole. This can occur when the rules of nutrition are violated - the consumption of large quantities of refined foods with low content dietary fiber, excess food, etc.

Under these conditions, the so-called putrefactive bacteria, releasing in the process of life substances 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 the wave-like movements of the colon (peristalsis) and reach the rectum - the last section, which serves to accumulate and excrete them. 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 intestinal tract, however, 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 immune functions 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.

The anti-infective protection performed by intestinal microorganisms is largely associated with the antagonism of representatives 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 the immune response of the macroorganism, stimulation of peristalsis, creation of an unfavorable environment, modification/ deconjugation bile acids(as one of the ways to modify environmental conditions), the 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 provide 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.

Other important function microflora is to convert bilirubin to urobilinogen, which is partially absorbed and excreted in the urine, and partially excreted in the feces.

Finally, the participation of the colon microflora in lipid metabolism. 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 ileum, conjugated cholic acid in the colon, it 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 cholesterol synthesis. 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 chemical compounds, among which vitamin K1 is distinguished - phylloquinone - plant origin, as well as vitamin K2 - a group of compounds called menaquinones - synthesized by microflora in small intestine. The synthesis of menaquinones is stimulated with a lack of phyloquinone in the diet and may increase with overgrowth small intestinal 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).

Fulfillment of the above and many others 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 must be eliminated under conditions reduced values pH, which is provided by short-chain fatty acids formed as a result of the metabolism of prebiotics. The detoxifying effect of non-digestible disaccharides (lactulose) is quite 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 on a natural or artificial feeding. 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 mixtures based on cow's milk without prebiotics, streptococci, bacteroids, representatives of Enterobacteriacea are predominant. Accordingly, the spectrum of bacterial metabolites in the intestine changes, as well as the nature of metabolic processes. 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. The laxative effect when taken in sufficient doses is provided by sources high concentration sugar, honey, beet 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 products devoid of ballast substances ( 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 end section digestive tract participates 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 by the body nutrients. 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.

The digestibility of nutrients is influenced by many factors: the composition of food, including the amount of ballast compounds, the technological processing of products, their combination, functional state 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.

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Physiology of nutrition

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The digestive tract is open system, through which the contact of the macroorganism with the external environment, including the microorganisms present in it, is carried out. The macroorganism and its microflora are in a state of dynamic equilibrium. The interactions between the macroorganism and the microbial associations inhabiting it are in the nature of symbiosis, that is, they turn out to be beneficial for both parties.

The vital activity of the intestinal microflora consumes up to 10% of the energy received and 20% of the volume of food taken by a person.

Biomass of microorganisms inhabiting the intestines of an adult healthy person, is 2.5 - 3 kg (approximately 5% of its total weight) and includes up to 450 - 500 various kinds microorganisms.

The large intestine contains about 1.5 kg of various microorganisms. About 2 billion microbial cells (representatives of 17 families, 45 genera, 500 species) are found in 1 gram of the contents of the caecum. The population density of microorganisms increases to distal department small intestine, increases sharply in the large intestine, reaching maximum values at the level of the colon. The human large intestine most colonized by microorganisms. The number of bacteria in the faeces can reach 5x10 12 CFU / g of content (the number of colony-forming microorganisms - colony-forming units - per 1 gram of feces). In the rectum, the density of seeding is up to 400 billion bacteria per 1 gram of content.

The composition of the microflora of the colon of a healthy person.

The dominant group characteristic of eubiosis in healthy adults is anaerobic bacteria, which account for up to 90-98% of the total number of intestinal microorganisms. Anaerobic microorganisms are microbes that can exist without free oxygen.

In contrast to them, the vital activity of aerobic flora is possible only in the presence of free oxygen. Aerobic and conditionally anaerobic bacteria, represented by Escherichia coli, streptococci, enterococci, make up no more than 5-10% of the total autoflora inhabiting the human intestine.

The ratio between intestinal anaerobes and aerobes is normally 10:1.

Anaerobic microflora (90-98%):

Bifidobacteria.

Bacteroids.

Lactobacilli.

Fusobacteria.

Anaerobic cocci.

Veylonella.

· Clostridia.

Aerobic microflora (less than 10%):

· Escherichia coli.

Streptococci (Enterococcus, Hemolyzing Streptococcus).

· Staphylococci.

Klebsiella.

Campylobacter.

Serrations.

Enterobacter.

Citrobacter.

Yeast-like mushrooms.

Proteus.

Classification of the normal microflora of the large intestine of a healthy person.

Normal intestinal microflora in quantitative ratios is represented by three main groups:

Basic or obligate microflora. Mandatory for the colon. These are mainly gram-positive non-spore anaerobes - bifidobacteria and gram-negative bacteroids. It makes up 90-95% of human microbiocenosis.

Associated microflora. Represented mainly by aerobes - lactobacilli, coccal forms, coli(E.coli). In total, these microorganisms do not exceed 5% of the microbiocenosis. Lactobacilli and E.coli are synergists of bifidobacteria.

Residual microflora (conditionally pathogenic or facultative microflora). This group includes staphylococci, candida, proteus, Pseudomonas aeruginosa, enterobacteria, campylobacter. The share of this group normally does not exceed 1% of the total number of microorganisms.

When used as a criterion for the constant or periodic presence of bacteria in the intestine, the microflora of healthy people is divided into several types:

Indigenous, or resident, or obligate (bibifidobacteria, lactobacilli, E. coli, bacteroids, enterococci).

Facultative, or non-permanent (staphylococci, proteus, clostridia, campylobacter, klebsiella, micrococci, some Escherichia.).

Random, or transient (Pseudomonas aeruginosa, pathogenic enterobacteria).

By localization in the intestine, microorganisms can also be divided into the following two groups, which differ from each other in quantitative and quality characteristics:

Mucoid (mucosal) microflora (M-microflora), which includes microorganisms (mainly bifidobacteria and lactobacilli), closely associated with the epithelium of the intestinal mucosa.

Cavitary microflora (P-microflora), represented by microorganisms that are localized in the intestinal lumen (bacteroids, veillonella, enterobacteria).

Depending on the nutrients that are broken down by the microflora, bacteria are divided into:

Proteolytic bacteria - bacteroids, proteus, clostridia, E. coli.

Saccharolytic bacteria - bifido- and lactobacilli, enterococci.

Features of microflora various departments human digestive tract.

Oral cavity.

AT oral cavity find about 300 species of bacteria, they are mainly represented by aerobes. 1 ml of saliva contains up to 10 9 microbial cells.

Due to the bactericidal and proteolytic action of acidic gastric juice, its contents on an empty stomach are sterile or total microbes in the stomach is no more than 10 3 cells in 1 ml.

Immediately after a meal, this figure can increase to 10 5 -10 7 cells in 1 ml of gastric contents.

In the stomach of healthy people, bacteria resistant to the action of of hydrochloric acid: L. fermentum, L. acidophialus, L. coli, L. brevis, yeast-like fungi genus Candida, streptococci, staphylococci.

Small intestine.

The contents of the small intestine in the proximal sections are sterile or close in composition to the gastric one. So, in the duodenum and jejunum of a healthy person total number microorganisms does not exceed 10 3 -10 5 microbial cells in 1 ml.

The dominant representatives of the microflora are staphylococci, streptococci, lactobacilli. Representatives of the Enterobacteriaceae family are normally absent.

As you approach ileum diplostreptococci, lactic acid bacilli, enterococci can be sown (in the amount of not more than 10 3 -105 microbial cells per 1 ml). In the ileum, the number of microbes approaches the composition of the colon microflora, their number reaches 10 5-10 8 bacteria per 1 ml. The ileocecal (bauginian) valve is a transitional zone between the microbiocenoses of the small and large intestine. In healthy people, it is a reliable obstacle to the spread of the microflora of the colon to the higher located sections of the gastrointestinal tract.

Colon.

1 ml of the contents of the colon contains 10 9 -10 12 bacteria, among which anaerobes (bifidobacteria, bacteroids) predominate.

The microbial spectrum and metabolic activity of microflora depend on the nature of nutrition. In people, long time located on vegetarian diet With large quantity vegetable fiber, the content of lactobacilli, enterococci, coliform bacteria (that is, microbes that contribute to the functional activity of the local immunity system) increases. With a predominance in the diet meat products there is an increase in the titer of Escherichia, Clostridia, the content of acidophilic bacteria decreases. Excessive alcohol consumption causes the death of bifidobacteria.

The physiological balance of the qualitative and quantitative composition of the microflora under conditions full health called "eubiosis" or normobiocenosis "

Table 1. Qualitative and quantitative composition of the main microflora of the large intestine in healthy people (CFU/g feces).

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 for a large number of 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 in the intestine pathogenic microbes, 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, are formed organic acids, 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 acid), mediators that affect the functions of the digestive and cardiovascular systems as well as on 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 substances 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 big influence on the level of population of microbes in each section of the intestinal tract, preventing their spread in the proximal direction. Therefore, violations motor activity intestines contribute to the occurrence of dysbacteriosis (changes in the quantitative ratios and composition of the microflora).