Nowadays, they are found in almost every second adult. At the same time, intermittent nausea, intestinal upset, heaviness in the abdomen or indigestion are worried. But not every person consults a doctor about this. Such an attitude can lead to serious consequences, because any disease is easier to cure at the initial stage. Therefore, if periodically there is discomfort in the abdomen, it is necessary to check the stomach and intestines. The examination will help to detect pathologies in time and prevent complications.
When to see a doctor
Only a doctor can determine if the digestive system is functioning properly. Therefore, in case of disruption of the digestive tract, it is necessary to consult a gastroenterologist. It is especially important to examine children on time, since their pathologies can progress rapidly, which seriously affects the state of the body.
- increased gas production, bloating;
- nausea, periodic vomiting;
- constipation or diarrhea;
- the appearance of pain in the abdomen or side;
- feeling of heaviness after eating;
- frequent belching or heartburn;
- the presence of impurities of mucus, blood or undigested food in the feces;
- decreased appetite.
It is also recommended to periodically examine the gastrointestinal tract for people with chronic pathologies of the digestive system. It can be gastritis, peptic ulcer, pancreatitis, reflux, colitis, duodenitis, biliary dyskinesia. Older people need regular check-ups of their intestines in order to detect the presence of a tumor in time.
Diagnostic procedures
Even an experienced doctor is not always able to determine the cause of the ailment by external symptoms. Moreover, not every person can describe what he feels. Therefore, the diagnosis of gastrointestinal diseases has its own sequence and is not complete without instrumental and laboratory examination. Some pathologies at the initial stage do not show specific symptoms, but gradually progress. Therefore, an examination of the gastrointestinal tract is very important for the timely detection of diseases and the appointment of the correct treatment. It is recommended to periodically pass it even for healthy people.
Before making a preliminary diagnosis and choosing examination methods, the doctor conducts a conversation with the patient. It is necessary to tell in detail about your feelings, how they are provoked when they arise. At the same time, the doctor is interested not only in the patient's complaints. The specialist will definitely ask about habits, diet, and the presence of chronic diseases. It is also very important what parents and close relatives are ill with. After this, the patient is examined. The doctor does this using physical methods.
These include palpation, percussion, and auscultation. At first glance, it may seem that such an external examination is useless to determine the state of internal organs. But for an experienced specialist, even such a survey is informative. First, an examination of the oral cavity is carried out, in which the digestion process begins. The condition of the mucous membrane, teeth, the color of the tongue is important.
The examination begins with a conversation and a general examination of the patient
Then the doctor feels the abdomen of the patient, determining whether the organs of the digestive system are enlarged, whether there are hardenings, scars, enlarged veins. Palpation also allows you to determine the shape of the organs, their soreness and location. Auscultation or listening allows you to hear what sounds the intestines make during work. Percussion is tapping, which allows you to clarify the shape, location and condition of internal organs.
After that, the doctor determines what other methods of examination of the gastrointestinal tract are still needed by the patient. There are quite a few of them, but 2-3 methods are usually chosen. It can be:
- PH-metry;
- fibrogastroduodenoscopy;
- sounding;
- x-ray examination;
- colonoscopy;
- scintigraphy;
- CT or MRI;
- analyzes of blood, urine and feces.
Instrumental examination methods make it possible to assess the state of the mucous membrane of the digestive tract, secretion of gastric juice, acidity level, and motor function. They can be used to detect the presence of tumors, cysts, erosions or ulcers. Usually, for the diagnosis of gastrointestinal diseases, the doctor prescribes EGD and blood tests. Sometimes it is still required, bile ducts and pancreas. Such a complete examination of the digestive system is necessary when the diagnosis is difficult.
If a person doubts whether his digestive organs are working normally and whether he should go to the doctor, you can check the stomach and intestines on your own. To do this, squeeze half a glass of juice from raw beets and leave it for a couple of hours. Then drink and watch the bowel movement. If it happens quickly and the feces are beetroot, then the stomach and intestines are working normally. If the urine becomes colored, and the stool will not last long, you should consult a doctor.
Gastroscopy
To examine the condition of the mucous membrane of the stomach and duodenum, endoscopic examination or fibrogastroduodenoscopy is most often used. This is the most accurate method for detecting gastrointestinal diseases at the initial stage. Gastroscopy is probing. The patient swallows a special flexible tube with a camera at the end. The doctor can use it to examine in detail the condition of the mucous membrane of the esophagus, stomach and duodenum. Probing allows you to diagnose peptic ulcer disease, inflammation of the mucous membrane in time, take gastric juice for analysis to determine its acidity.
Endoscopic examination can cause discomfort to the patient, although modern devices for this make the procedure as comfortable as possible. But many patients refuse it because of fear of pain or gagging. In this case, as well as for examination of the small intestine, capsule intubation may be prescribed. This is a modern, minimally invasive diagnostic method. The patient is offered to swallow a special capsule with a video camera. As it moves through the digestive tract, it will transmit an image to the monitor. Then the capsule comes out naturally.
Gastroscopy is the most informative method for examining the upper digestive tract.
X-ray
X-ray diagnostics is the most accessible and cheapest examination method. It allows you to assess the thickness of the walls of organs, their shape and size, to see the presence of ulcers, erosions and neoplasms.
One of the types of X-ray examination of the gastrointestinal tract is irrigoscopy. This is the name of the examination with the use of contrast agents. When examining the stomach, the patient is given a capsule of barium to drink, and for a picture of the intestines, this substance is injected through the anus. Barium is opaque to X-rays, which makes it possible to get a more accurate picture.
Ultrasound
Modern devices for ultrasound diagnostics allow you to clearly see the size, location and shape of internal organs, the presence of foreign bodies and tumors. Usually, it is with an ultrasound scan that diagnostics begins when a patient turns to a doctor with complaints of abdominal discomfort. This method can be used for preventive purposes, for the timely detection of tumors, decreased intestinal motility, narrowing of the intestinal lumen, and disruption of the sphincters.
Ultrasound examination of the gastrointestinal tract is also used to confirm the diagnosis and to control the correctness of treatment. It is necessary for gastritis, gastroduodenitis, colitis, irritable bowel syndrome, the presence of polyps or cysts, gallstone disease, pancreatitis. Informative ultrasound for bowel examination. Some preparation is required before the procedure. And before the scan itself, fluid is injected into the intestines. So you can identify the presence of polyps, tumors, narrowing of the intestinal lumen.
Tomography
If difficulties arise in diagnosis, computed tomography may be prescribed. It allows you to obtain information about the shape and size of the digestive system, the condition of bones and muscles, the thickness of the abdominal wall, the presence of foreign bodies. CT is more informative than X-ray, but the radiation exposure from such an examination is less.
More accurate information about the state of the gastrointestinal tract can be obtained using MRI. This allows you to examine the stomach, intestines, liver, pancreas, gallbladder and ducts. An MRI scan allows you to assess the condition of blood vessels and lymph nodes, the presence of stones, cysts, polyps or tumors, and the structure of organ tissues.
Bowel examination
Due to the peculiarities of the structure and location of this organ, it is difficult to examine it. The condition of the duodenum can be determined by endoscopy through the esophagus. But the probe does not penetrate further. The rectum is visible during colonoscopy. But the small intestine is more difficult to examine. To identify its pathology, a comprehensive examination is required using several methods.
The most commonly used colonoscopy is an examination of the rectum with a probe. It is inserted through the anus. With the help of a special camera at its end, you can examine the condition of the intestinal walls, the presence of tumors or stagnation of feces. During the procedure, you can take a sample of the mucous membrane for analysis or even remove small polyps. And retromanoscopy also allows you to assess the condition of the large intestine. In this case, a special probe moves over a distance of more than 30 cm. It is recommended to undergo such an examination for every person after 50 years. This allows early detection of cancer.
Analyzes
Any research methods require some preparation, without which the result can be distorted. It is usually recommended to prepare for the diagnosis 3-5 days before the procedure. There are specific recommendations for each method, the doctor must warn the patient about them. But there are general recommendations that are related to the specifics of the location and functioning of the digestive system.
- Be sure to follow a diet a few days before the examination. To prevent gas formation, it is recommended to avoid legumes, black bread, a lot of fiber, and heavy foods. About 10-12 hours before the procedure, you should not eat at all, sometimes it is forbidden to even drink water.
- It is advisable to exclude alcohol intake and not smoke, especially 12 hours before the examination.
- Sometimes it is recommended to take certain medications to help cleanse the digestive tract and improve digestion. These are enterosorbents, enzymes, drugs against nausea and flatulence.
- When examining the intestines, you need to take laxatives or an enema for several days to cleanse it.
- An anesthetic or antispasmodic can be taken before probing. For some, a sedative is also recommended.
Contraindications
To check your gastrointestinal tract, you first need to see a doctor. It will help you decide which methods are best to use. After all, not all of them are equally informative, in addition, some have contraindications.
Instrumental examination is not carried out if the patient has an infection, fever, acute inflammation. It is also contraindicated in the presence of heart or lung disease, bleeding disorders, allergies to certain drugs.
Regular examination of the gastrointestinal tract will help identify various pathologies at the initial stage. Thanks to this, it will be easier to cure them without complications.
In the gastrointestinal – the human intestinal tract is found obligate (main microflora), facultative (opportunistic and saprophytic microflora) and transient microflora (microorganisms accidentally got into the gastrointestinal tract).
In the esophagus and stomach, a transient microflora is usually determined, which enters them with food or from the oral cavity. Despite the ingestion of a large number of microbes into the stomach, a small number of microorganisms (less than 10 3 CFU / ml) is normally detected in the stomach in healthy people. This is due to the acidic pH of the contents of the stomach and the bactericidal properties of gastric juice, which reliably protects a person from the penetration of pathogenic and opportunistic bacteria into the intestines. Mostly acid-fast bacteria are found in gastric juice. – lactobacilli, yeast fungi. In some people, streptococci are determined in it, S. ventriculus, B. subtilis, anaerobic gram-positive cocci.
In the thickness of the gastric mucosa, anaerobes of Veilonella, bacteroids, and peptococci are found.
When studying healthy children aged 8 – For 15 years, staphylococci, streptococci, enterococci, corynebacteria, peptococci, lactobacilli and propionibacteria were detected in the mucous membrane of the antrum of the stomach. Microbiological examination of stomach contents is relatively rare.
The number and composition of microbes in the small intestine varies depending on the section of the intestine. The total number of microbes in the small intestine is no more than 10 4 – 10 5 CFU / ml of content. The low concentration of microbes is due to the action of bile, the presence of pancreatic enzymes, intestinal peristalsis, which ensures the rapid removal of microbes into the distal intestine; the production of immunoglobulins by the cells of the mucous membrane, the state of the intestinal epithelium and mucus secreted by the goblet cells of the intestine containing inhibitors of the growth of microbes. The microflora of the small intestine is represented mainly by gram-positive optional – anaerobic and anaerobic bacteria (enterococci, lactobacilli, bifidobacteria), yeast-like fungi, bacteroids and veilonella are less common, enterobacteria are extremely rare. After eating, the number of microbes in the small intestine can increase significantly, but then, in a short time, it quickly returns to its original level. In the lower parts of the small intestine (in the ileum), the number of microbes increases and can reach 10 7 CFU / ml of contents.
In the large intestine, gram-positive flora changes to gram-negative. The number of obligate anaerobes begins to exceed the number of facultative anaerobes. Representatives of microbes characteristic of the large intestine appear.
The growth and development of microbes in the large intestine is facilitated by the absence of digestive enzymes, the presence of a large amount of nutrients, prolonged presence of food, structural features of the mucous membrane and, in particular, the mucous overlays of the large intestine. They determine the organ tropism of some species of anaerobic bacteria, which, as a result of their vital activity, form products used by the facultative anaerobic flora, which in turn create conditions for the life of obligate anaerobes.
In the human large intestine there are more than 400 species of various microbes, and the number of anaerobes is 100 – 1000 times the number of facultative anaerobes. Obligate anaerobes make up 90-95% of the total composition. They are represented by bifidobacteria, lactobacilli, bacteroids, veilonella, peptostreptococci, clostridia and fusobacteria (Fig. 1)
The share of other microorganisms is 0.1 – 0.01% is a residual microflora: enterobacteria (Proteus, Klebsiella, Serrata), enterococci, staphylococci, streptococci, bacilli, yeast fungi (Fig. 3). Conditionally pathogenic amoebas, Trichomonas, some types of intestinal viruses can live in the intestine.
The role and methods of bacteriological research in the diagnosis of diseases of the gastrointestinal tract
Bacteriological research
Bacteria and fungi are found in large quantities in the intestines and perform a number of important functions: vitamin-forming, protective (due to competition with opportunistic and pathogenic flora), digesting (due to the content of various enzymes in them). Activation in the intestine of any one group (putrefactive, fermentative or pathogenic) leads to a change in the normal ratio of microflora - dysbiosis. Dysbacteriosis complicates the course of most gastrointestinal diseases.
Medicinal dysbacteriosis (fungal, staphylococcal, Pseudomonas aeruginosa, Proteus), which develops during treatment with antibacterial drugs, often proceeds severely, with untimely diagnosis it often leads to sepsis, shock, sometimes fatal.
The diagnosis of dysbiosis is made on the basis of bacteriological examination of feces, that is, by sowing feces on nutrient media with further identification of microorganisms.
Identification of intestinal microbial contamination. Microbial contamination of the intestine is characterized by excessive growth of opportunistic microorganisms (Escherichia, Klebsiella, enterococci, lactobacilli) and suppression of the growth of bifidobacteria and other microorganisms related to protective factors.
The main reasons for the overgrowth of opportunistic microorganisms
- acute gastroenteritis or enterocolitis suffered in the recent past;
- diseases accompanied by impaired digestion and absorption of food in the small intestine (congenital or acquired deficiency of lactase, sucrase and other enzymes of hydrolysis of disaccharides, celiac disease (gluten deficiency), achlorhydria, achilia, secretory pancreatic insufficiency, biliary excretion);
- diseases accompanied by impaired motor function of the small intestine (diverticula, intestinal strictures in Crohn's disease, radiation damage, after surgery on the abdominal organs; obstruction in small intestine tumors; intestinal dyskinesia, for example, in diseases of the biliary tract);
- chronic diseases of internal organs, accompanied by signs of immunodeficiency (HIV infection, diabetes mellitus, infectious diseases, scleroderma, etc.);
- massive long-term therapy with broad-spectrum antibiotics.
As a result of microbial contamination of the intestine, structural changes in its mucous membrane occur (flattening of the villi, inflammatory infiltration of the lamina propria), which leads to persistent impairment of the absorption of water and food, the development of prolonged, refractory to treatment, diarrhea and other dyspeptic disorders and the appearance of signs of malabsorption.
Bacteriological tests to detect bacterial overgrowth in the intestine
Revealing bacterial overgrowth in the intestine is possible in several ways, 2 of which are the most informative:
- bacteriological examination of jejunal aspirates;
- hydrogen breath test.
Bacteriological examination of jejunal aspirates |
With microbial contamination, it can reveal a significant increase in the total number of microorganisms in 1 ml of intestinal juice (more than 100 / ml), as well as the predominance of opportunistic microflora. For the study, a long two-meter polyethylene probe is used, inserted through an endoscope with a biopsy channel to a depth of about 35 cm beyond the gatekeeper. | ||||||||||
Hydrogen breath test |
Belongs to a group of numerous indirect methods for determining bacterial colonization of the small intestine. It is based on the ability of most bacteria to enzymatically break down carbohydrates, during which hydrogen is formed, which, after being absorbed into the blood, is excreted from the body during respiration. The study is carried out in the morning on an empty stomach. First, an initial sample of exhaled air is obtained, for this the patient takes a deep breath and maximum exhalation into a modified Haldane-Priestley tube. At the end of the expiration, 30 ml of air is drawn into a plastic syringe. Then the patient takes 50 g of lactulose (or glucose) orally. Samples of exhaled air (30 ml each) are collected for 3 hours every 20 minutes in the manner described. All samples obtained are analyzed on a hydrogen analyzer. Normally, the amount of hydrogen in exhaled air increases moderately, and the peak in hydrogen concentration occurs 2 hours or more after the start of the study. With bacterial overgrowth in the small intestine, the peak concentration of H 2 (more than 20 r / min) is usually achieved within the first hour. The hydrogen breath test is quite simple and safe, although its sensitivity is lower than that of a bacteriological study of jejunal aspirate. Microhelminthological methods are used to detect eggs or larvae of helminths. Native smears or fixed stained preparations are prepared for research. When examining enterobiasis, methods of scraping from perianal folds with a wooden spatula or cotton swab are used. From the scrapings, preparations are prepared, which are examined under a microscope. To control the treatment, the entire portion of feces is sent to the laboratory on the days of taking the antihelminthic agent. X-ray research methodsThe X-ray method for examining the intestines gives an idea of \u200b\u200bthe location of various parts of the intestine, their shape, the state of the motor-evacuation function (tone and peristalsis), allows you to identify inflammation in the intestinal mucosa, diagnose expansion or narrowing, determine changes in the relief of the mucous membrane and assess the motor activity of the intestine ... Basic methods:
Endoscopic methods of bowel examinationColonoscopy
Along with X-ray examination, endoscopy is currently considered as the main method for diagnosing diseases of the stomach and intestines at the earliest stages of their development. Colonoscopy is used to diagnose the following diseases:
Among all the known instrumental research methods, only with endoscopy it is possible to study in detail the smallest changes in the mucous membrane, to recognize the sources of bleeding, and to carry out dynamic monitoring of the course of pathological processes. In addition, with the help of endoscopy, various surgical and therapeutic procedures can be performed directly under visual control. The colonoscopy method is quite safe, but it requires special skills due to the anatomical features of the colon, which has a number of natural curves and physiological sphincters. Before colonoscopy, it is advisable to carry out sigmoidoscopy and digital examination of the rectum.
Preparing a patient for a planned colonoscopy:
The study is carried out by the doctor in the position of the patient lying on his left side. After the examination, the patient must be monitored and calm. If necessary, a targeted biopsy of the colon mucosa may be performed during colonoscopy. SigmoidoscopyThrough sigmoidoscopy, pathological changes in the mucous membrane can be detected (malignant and benign neoplasms, inflammatory processes, ulceration, hemorrhoids, fistulas). In the study, you can get smears and scrapings from the mucous membrane for bacteriological and cytological examination, conduct a biopsy, some therapeutic and surgical manipulations. Preparing the patient for the study: The examination is carried out by the doctor in the supine position of the patient with raised and extended lower extremities (when using a flexible rectoscope) or in the knee-elbow position (when using a rigid rectoscope). The rectoscope is inserted to a depth of 25-30 cm. After the examination, the patient must be monitored and calm. LaparoscopyLaparoscopy is a method of visually examining the abdominal cavity through an endoscope (laparoscope) inserted through the abdominal wall. Examination of the abdominal cavity, if necessary, is combined with targeted biopsy of the liver and sometimes the pancreas. Laparoscopy is performed for urgent diagnosis and emergency surgery (for example, peritonitis or ascites of unknown origin, suspected mesenteric thrombosis and intestinal infarction), as well as for endoscopic operations on the abdominal organs. Laparoscopy allows you to determine the size of some organs of the abdominal cavity, to assess the nature of their surface, the color of the serous membrane, the presence of focal superficial formations, etc. Since laparoscopy is an invasive method, it is performed only in a surgical hospital in compliance with all the rules of asepsis and antiseptics. Contraindications for laparoscopy:
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In recent years, in connection with the use of special flexible fiber optic endoscopes, colonoscopy has become one of the most important diagnostic methods.BASIC FUNCTIONS OF NORMAL INTESTINAL MICROFLORA
Normal microflora (normal flora) of the gastrointestinal tract is a necessary condition for the vital activity of the body. The microflora of the gastrointestinal tract in the modern sense is considered as the human microbiome ...
Normoflora (microflora in a normal state) orThe normal state of microflora (eubiosis) - it is qualitative and quantitativethe ratio of various populations of microbes of individual organs and systems, which maintains the biochemical, metabolic and immunological balance necessary to maintain human health.The most important function of microflora is its participation in the formation of the body's resistance to various diseases and ensuring the prevention of colonization of the human body by foreign microorganisms.
The gastrointestinal tract is one of the most complex microecological environments of the human body, in which, on the total area of \u200b\u200bthe mucous membrane, which is about 400 m 2, there is an extremely high and varied (over 1000 speciesheterogeneous bacteria, viruses, archaea and fungi - ed.) the density of microbial contamination, in which the interaction between the protective systems of the macroorganism and microbial associations is very delicately balanced. It is believed that bacteria make up 35 to 50% of the volume of the human colon, and their total biomass in the gastrointestinal tract is close to 1.5 kg.However, bacteria are unevenly distributed in the digestive tract. If the density of microbial colonization in the stomach is low and is only about 10 3 -10 4 CFU / ml, and in the ileum - 10 7 -10 8 CFU / ml, then already in the area of \u200b\u200bthe ileocecal valve in the colon, the density gradient of bacteria reaches 10 11 -10 12 CFU / ml. Despite such a wide variety of bacterial species inhabiting the gastrointestinal tract, most can be identified only molecularly and genetically.
Also, in any microbiocenosis, including intestinal, there are always species of microorganisms that are constantly living - 90% related to the so-called. obligate microflora ( synonyms: the main, autochthonous, indigenous, resident, obligatory microflora), which is assigned a leading role in maintaining symbiotic relations between the macroorganism and its microbiota, as well as in the regulation of intermicrobial relations, and there are also additional (concomitant or facultative microflora) - about 10% and transient ( random species, allochthonous, residual microflora) - 0.01%.
The main types intestinal microbiota are Firmicutes, Bacteriodetes, Actinobacteria, Proteobacteria, Fusobacteria, Verrucomicrobia, Tenericutesand Lentisphaerae.
Among commensal bacteria cultured from the gastrointestinal tract, more than 99.9% are obligate anaerobes, of which the dominant are childbirth : Bacteroides, Bifidobacterium, Eubacterium, Lactobacillus, Clostridium, Faecalibacterium, Fusobacterium, Peptococcus, Peptostreptococcus, Ruminococcus, Streptococcus, Escherichia and Veillonella... The composition of bacteria found in different parts of the gastrointestinal tract is highly variable.
Magnification density microorganisms and biodiversity is observed along the gastrointestinal tract in the caudal-cervical direction. Differences in intestinal composition are also observed between the intestinal lumen and the mucosal surface. Bacteroides, Bifidobacterium, Streptococcus, Enterococcus, Clostridium, Lactobacillus and Ruminococcus are predominant childbirth in the intestinal lumen, while Clostridium, Lactobacillus, Enterococcus and Akkermansia are predominant on the surface associated with the mucous membrane, i.e. this is andmicrobiota, respectively (or in another way - luminal and mucous). The microbiota associated with the mucosa plays a very important role in maintaining homeostasis, given its proximity to the intestinal epithelium and the main immune system of the mucosa [3 ]. This microbiota may play an important role in maintaining host cellular homeostasis or in triggering inflammatory mechanisms.
Once this composition is established, the gut microbiota remains stable throughout adulthood. There are some differences between the gut microbiota of the elderly and young adults, primarily related to the prevalence of childbirth Bacteroides and Clostridium in the elderly and type Firmicutes in young adults. Three variants of the human gut microbiota have been proposed, classified as enterotypes based on the variation of the levels of one of the three childbirth: Bacteroides (enterotype 1), Prevotella (enterotype 2) and Ruminococcus (enterotype 3). These three options, apparently, do not depend on body mass index, age, gender or nationality [,].
Depending on the frequency and constancy of the detection of bacteria, the entire microflora is divided into three groups (Table 1).
Table 1. Microbiocenosis of the gastrointestinal tract.
Microflora type |
Main representatives |
|
|
Permanent (indigenous, resistant) |
Obligate (main)(90%) |
Bacteroids, bifidobacteria |
|
Optional (concomitant) (~ 10%) |
Lactobacillus, Escherichia, Enterococci, Clostridia * |
|
|
Random (transient) |
Residual (<1%) |
Klebsiella, proteus, staphylococcus, citrobacter, yeast |
However, this division is extremely arbitrary.... Directly in the colon human, bacteria of the genera Actinomyces, Сitrobacter, Сorynebacterium, Peptococcus, Veillonella, Аcidominococcus, Аnaerovibrio, Вutyrovibrio, Acetovibrio, Campylobacter, Disulfomonas, Roseburia, Ruminococcus, Spomonlenella. In addition to these groups of microorganisms, you can also find representatives of other anaerobic bacteria (Gemiger, Anaerobiospirillum, Metanobrevibacter, Megasphaera, Bilophila), various representatives of the non-pathogenic protozoan genera Chilomastix, Endolimax, Entamoeba, Enteromonas) and more than ten intestinal viruses and the same 75 species of bacteria, and more than 90% of the bacteria in the colon belong to the types Bacteroidetes and Firmicutes - Qin, J .;et al... A human gut microbial gene catalog established by metagenomic sequencing.Nature.2010 , 464 , 59-65.).
As noted above, the division of gastrointestinal tract microorganisms into groups of "constancy and importance" is rather arbitrary. Science does not stand still, and taking into account the emergence of new culture-independent methods for identifying microbiota (DNA sequencing, fluorescent in situ hybridization (FISH), the use of Illumina technology, etc.), and the reclassification of a number of microorganisms carried out in connection with this, the view on the composition and role of healthy human intestinal microbiota has changed markedly. As it turned out, the composition of the gastrointestinal microbiome depends on human accessories. A new understanding of the dominant species also appeared - a refined phylogenetic tree microbiota of the human gastrointestinal tract (about this and not only see the sections "" & " ".
There is a close relationship between the colonies of microorganisms and the intestinal wall, which allows them to be combined into a singlemicrobial tissue complex, which is formed by microcolonies of bacteria and the metabolites they produce, mucus (mucin), epithelial cells of the mucous membrane and their glycocalyx, as well as stromal cells of the mucous membrane (fibroblasts, leukocytes, lymphocytes, neuroendocrine cells, cells of the microvasculature, etc.). It is necessary to remember about the existence of another population part of the microflora -cavity(or as stated above - translucent), which is more variable and depends on the rate of intake of food substrates through the alimentary canal, in particular dietary fibers, which are a nutrient substrate and play the role of a matrix on which intestinal bacteria are fixed and form colonies. Cavity (luminal) Flora dominates in the fecal microflora, which makes it necessary to evaluate with extreme caution changes in various microbial populations detected during bacteriological research.
The stomach contains little microflora, much more of it in the small intestine and especially a lot in the large intestine. It should be noted that suctionfat-solubleessential substances vitamins and trace elements occurs mainly in the jejunum. Therefore, the systematic inclusion in the diet and probiotic products and dietary supplements thatmodulate the intestinal microflora (microbiota), which regulates the processes of intestinal absorption,becomes a very effective tool in the prevention and treatment of nutritional diseases.
Intestinal absorption - this is the process of the entry of various compounds through the layer of cells into the blood and lymph, as a result of which the body receives all the substances it needs.
The most intense absorption occurs in the small intestine. Due to the fact that small arteries branching into capillaries penetrate into each intestinal villi, the absorbed nutrients easily penetrate into the body's fluids. Glucose and proteins, broken down to amino acids, are absorbed into the bloodstream mediocre. The blood, which carries glucose and amino acids, is sent to the liver, where carbohydrates are deposited. Fatty acids and glycerin - a product of fat processing under the influence of bile - are absorbed into the lymph and from there enter the circulatory system.
In the picture on the left (diagram of the structure of the villi of the small intestine): 1 - cylindrical epithelium, 2 - central lymphatic vessel, 3 - capillary network, 4 - mucous membrane, 5 - submucosa, 6 - muscle plate of the mucous membrane, 7 - intestinal gland, 8 - lymphatic canal ...
One of the meanings of microflora large intestine lies in the fact that it is involved in the final decomposition of undigested food residues.In the large intestine, digestion is completed by hydrolysis of undigested food debris. During hydrolysis in the large intestine, enzymes from the small intestine and enzymes from intestinal bacteria are involved. There is absorption of water, mineral salts (electrolytes), the breakdown of plant fiber, the formation of feces.
Microflora plays a significant (!) role inperistalsis, secretion, absorption and cellular composition of the intestine. Microflora is involved in the decomposition of enzymes and other biologically active substances. Normal microflora provides colonization resistance - protection of the intestinal mucosa from pathogenic bacteria, suppressing pathogenic microorganisms and preventing the infection of the body.Bacterial enzymes break down undigested in the small intestine. The intestinal flora synthesizes vitamin K and b vitamins, a number of irreplaceable amino acids and enzymes necessary for the body.With the participation of microflora in the body, the exchange of proteins, fats, carbons, bile and fatty acids occurs, cholesterol, pro-carcinogens (substances that can cause cancer) are inactivated, excess food is utilized and feces are formed. The role of normal flora is extremely important for the host organism, which is why its violation (dysbacteriosis) and the development of dysbiosis in general leads to serious metabolic and immunological diseases.
The composition of microorganisms in certain parts of the intestine depends on many factors:lifestyle, nutrition, viral and bacterial infections, and medication, especially antibiotics. Many diseases of the gastrointestinal tract, including inflammatory ones, can also disrupt the gut ecosystem. Common digestive problems result from this imbalance: bloating, indigestion, constipation or diarrhea, etc.
For more information on the role of the gut microbiome in maintaining gastrointestinal health, see: (see incl. links at the bottom of this section).
In the figure: Spatial distribution and concentration of bacteria along the human gastrointestinal tract ( averaged data).
The gut microflora (gut microbiome) is an unusually complex ecosystem. One individual has at least 17 families of bacteria, 50 genera, 400-500 species, and an indefinite number of subspecies. The intestinal microflora is divided into obligate (microorganisms that are constantly part of the normal flora and play an important role in metabolism and anti-infectious protection) and facultative (microorganisms that are often found in healthy people, but are opportunistic, i.e., capable of causing diseases with a decrease resistance of the macroorganism). The dominant representatives of the obligate microflora are bifidobacteria.
Table 1 shows the most famousthe functions of the intestinal microflora (microbiota), while its functionality is much broader and is still being studied
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Table 1. Main functions of the intestinal microbiota |
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Main functions |
Description |
|
Digestion |
|
|
Protective functions |
Synthesis of immunoglobulin A and interferons by colonocytes, phagocytic activity of monocytes, plasma cell polyiferation, formation of colonization resistance of the intestine, 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 (catalyzes the decarboxylation reaction of keto acids, is a carrier of aldehyde groups); В 2 (electron carrier with NADH); B 3 (transfer of electrons to O 2); B 5 (precursor of coenzyme A, is involved in lipid metabolism); B 6 (carrier of amino groups in reactions involving amino acids); At 12 (participation in the synthesis of deoxyribose and nucleotides); |
|
Detoxification function |
incl. neutralization of certain types of drugs and xenobiotics: acetaminophen, nitrogen-containing substances, bilirubin, cholesterol, etc. |
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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 of 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 course of digestion and absorption in the intestine, takes part in the maturation of cells of the immune system, which enhances the protective properties of the body, etc. ...The two main functions of normal microflora are: barrier against pathogenic agents and stimulation of an immune response: BARRIER ACTION. Intestinal microflora hassuppressing effect on the reproduction of pathogenic bacteria and thus prevents pathogenic infections.
For example, bacteria of the parietal (mucous) microflora occupy certain receptors on the surface of epithelial cells. Pathogenic bacteriathat 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. (in particular, propionic acid bacteria P. freudenreichii have fairly good adhesive properties and adhere to intestinal cells very reliably, creating the aforementioned protective barrier. Also, the bacteria of the permanent microflora help maintain intestinal motility and the integrity of the intestinal mucosa. So, bacteria - commensals of the large intestine during the catabolism of non-digestible 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 the barrier functions of the mucin layer mucus (increase the production of mucins and the protective function of the epithelium). INTESTINAL IMMUNE SYSTEM. More than 70% of immune cells are concentrated in the human intestine. The main function of the intestinal immune system is to prevent bacteria from entering the bloodstream. The second function is to eliminate pathogens (disease-causing bacteria). This is provided by two mechanisms: congenital (inherited by the child from the mother, people have antibodies in the blood from birth) and acquired immunity (appears after foreign proteins enter the bloodstream, for example, after suffering an infectious disease). Upon contact with pathogens, the body's immune defense is stimulated. When interacting with Toll-like receptors, the synthesis of various types of cytokines is triggered. The intestinal microflora affects specific accumulations of lymphoid tissue. This stimulates the cellular and humoral immune response. The cells of the intestinal immune system actively produce secretory immunolobulin A (LgA), a protein that is involved in providing local immunity and is an 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 defense.The normal intestinal microflora plays a particularly important role in the life of the body of newborns and children. Due 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 medium, 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 in the picture Left: Colony of acidophilus bacillus (x 1100), On right: Destruction of Shigella flexneri (a) (Shigella Flexner is a species of bacteria, causative agents of dysentery) under the action of bacteriocin-producing cells of acidophilus bacillus (x 60,000)
It should be especially noted that in the intestine, almost all microorganismshave a special form of coexistence called biofilm. Biofilm iscommunity (colony)microorganisms located on any surface, the cells of which are attached to each other. Usually cells are immersed in an extracellular polymeric substance secreted by them - mucus. It is the biofilm that performs the main barrier function against the penetration of pathogens into the blood, by eliminating the possibility of their penetration to epithelial cells. For more information on biofilm, see: HISTORY OF STUDYING THE GIT MICROFLORA COMPOSITION The history of studying the composition of the microflora of the gastrointestinal tract (GIT) began in 1681, when the Dutch researcher Anthony Van Leeuwenhoek first reported on his observations of bacteria and other microorganisms found in human feces, and put forward a hypothesis about the coexistence of various 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 doctor Robert Koch continued his research in this direction and created a technique for isolating pure cultures, which makes it possible to identify specific bacterial strains, which is necessary to distinguish between pathogenic and beneficial microorganisms. In 1955 Peretz L.G. showed that intestinal coli of healthy people is one of the main representatives of normal microflora and plays a positive role due to its strong antagonistic properties in relation to pathogenic microbes. Studies begun more than 300 years ago on the composition of intestinal microbiocenosis, its normal and pathological physiology and the development of ways to positively influence the intestinal microflora continue at the present time. HUMAN AS A HABITAT FOR BACTERIAThe 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 live 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, in numbers - up to 10 14 CFU / g. Previously, it was believed that the composition of the microbiocenosis of the gastrointestinal tract includes 17 families, 45 genera, more than 500 species of microorganisms (recent data - about 1500 species) constantly corrected. Taking into account the 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 numbers 400 thousand genes, which is 12 times the size of the human genome. Exposed analysis on the homology of the sequenced 16S rRNA genes, parietal (mucosal) microflora of 400 different parts of the gastrointestinal tract, obtained by endoscopic examination of different parts of the intestines of volunteers. As a result of the study, it was shown that the parietal and luminal microflora includes 395 phylogenetically separate groups of microorganisms, of which 244 are completely new. At the same time, 80% of new taxa identified during molecular genetic research belong to uncultured microorganisms. Most of the putative new phylotypes of microorganisms are representatives of the genera Firmicutes and Bactero-ides. The total number of species is approaching 1500 and requires further clarification. The gastrointestinal tract through the sphincter system communicates with the external environment of the world around us and at the same time through the intestinal wall - with the internal environment of the body. Thanks to this feature, its own environment has been created in the gastrointestinal tract cavity, which can be divided into two separate niches: chyme and mucous membrane. The human digestive system interacts with various bacteria, which can be designated as "the endotrophic microflora of the human intestinal biotope." Human endotrophic microflora is divided into three main groups. The first group includes eubiotic indigenous or eubiotic transient microflora useful for humans; to the second - neutral microorganisms that are constantly or periodically sown from the intestines, but do not affect human life; to the third - pathogenic or potentially pathogenic bacteria ("aggressive populations"). CAVITY AND PARALLEL GIT MICROBIOTOPESIn microecological terms, the gastrointestinal biotope can be divided into tiers (oral cavity, stomach, intestines) and microbiotopes (cavity, parietal, and epithelial). The ability to be applied 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 the eubiotic or aggressive group, are the main criteria characterizing a microorganism interacting with the gastrointestinal tract. Eubi-o-tic bacteria are involved in the creation of colonization resistance of the organism, which is a unique mechanism of the system of anti-infectious barriers. Cavity microbiotope throughout the gastrointestinal tract is heterogeneous, its properties are determined by the composition and quality of the contents of one or another tier. The tiers have their own anatomical and functional features, therefore their contents differ in the composition of substances, consistency, pH, speed of movement and other properties. These properties determine the qualitative and quantitative composition of the cavity microbial populations adapted to them. Parietal microbiotope is the most important structure that limits the internal environment of the body from the external one. 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, beneficial or harmful to humans, arises - what we call symbiosis.
Today it is known that the microflora of the intestinal mucosa differs significantly from the microflora of the intestinal lumen and feces. Although every adult's gut is inhabited by a certain combination of predominant bacterial species, the composition of the microflora can vary depending on 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 affect the composition of the intestinal microflora more than nutrition.
Note to the picture: ALF - fundus of the stomach, AOZ - antrum of the stomach, duodenum - duodenum (:Chernin V.V., Bondarenko V.M., Parfenov A.I. Participation of the luminal and mucous 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, No. 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, then there are aerotolerant anaerobes (lactobacilli, etc.), then anaerobes, even higher, facultative ...The luminal microflora is the most variable and sensitive to various exogenous influences. Changes in diet, environmental impact, drug therapy, primarily affect the quality of the luminal microflora. See also: The number of microorganisms of mucosal and luminal microflora The mucous microflora is more resistant to external influences than the luminal microflora. The relationship between mucous and luminal microflora is dynamic, and is determined by the following factors:
MICROFLORA OF ORAL CAVITY, ESOPHAGUS AND STOMACHConsider the composition of the normal microflora of different parts of the gastrointestinal tract.
Saliva is the first digestive fluid that processes nutrients and affects the penetrating microflora. The total content of bacteria in saliva is variable and averages 10 8 MC / ml. The composition of the normal microflora of the oral cavity includes streptococci, staphylococci, lactobacilli, corynebacteria, a large number of anaerobes. In total, the microflora of the mouth has more than 200 types of microorganisms. On the surface of the mucous membrane, depending on the hygiene products used by the individual, about 10 3 -10 5 MK / mm2 are found. 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, possessing a high degree of histadhesion, inhibit the colonization of the mouth by fungi of the genus Sandida and staphylococci.
The main microorganisms active in the gastric environment are acid-fast representatives of the genus Lactobacillus, with or without histadhesion to mucin, some types of soil bacteria and bifidobacteria. Lactobacilli, despite the short residence time in the stomach, are capable, in addition to the antibiotic effect in the stomach cavity, to temporarily colonize the parietal microbiotope. As a result of the joint action of the protective components, the bulk of the microorganisms that enter the stomach die. However, if the mucous and immunobiological components are disrupted, some bacteria find their biotope in the stomach. So, due to the factors of pathogenicity in the gastric cavity, the population of Helico-bacter pylori is fixed.
BASIC FUNCTIONS OF THE SMALL INTESTINAL Small intestine
is a tube about 6m long. It occupies almost the entire lower abdomen and is the longest part of the digestive system, connecting the stomach to the large intestine. Most of the food is already digested in the small intestine with the help of special substances - enzymes (enzymes). To the main functions of the small intestineinclude cavity and parietal hydrolysis of food, absorption, secretion, and 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 cavity and wall hydrolysis, as well as in the processes of absorption of nutrients. The small intestine is one of the most important links ensuring long-term preservation of the eubiotic parietal microflora. There is a difference in the colonization of cavity 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 parietal 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 one approaches the distal parts of the small intestine, the total number of bacteria increases to 10 8 per 1 ml of contents, while additional species appear, including enterobacteria, bacteroids, and bifidobacteria. BASIC FUNCTIONS OF THE LARGE INTESTINAL
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In 1886, one of the founders of the doctrine of intestinal infections F. Esherich 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 that 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 embodiment of Mechnikov's ideas was the use of acidophilic lactobacilli for therapeutic purposes, which began in the United States in 1920-1922. Domestic researchers began to study this issue only in the 50s of the XX century.
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