Basic physiologic functions of intestinal bacterial flora, nutrient flow

An obligatory condition for the assimilation of food is the disassembly of its complex structures into simple compounds, which occurs during the digestion process. The released monomers (amino acids, monosaccharides, fatty acids, etc.) are devoid of species specificity and are predominantly the same for all organisms. In some cases, oligomers (di-, tri-, and occasionally tetramers) may be formed, which can also be assimilated. In higher organisms, the transport of oligomers has been demonstrated using dipeptides as an example. In this case, the assimilation of food is realized in three stages: extracellular (cavity) digestion - membrane digestion - absorption, and in a number of organisms - in four, with the participation of intracellular digestion.

Flow of hormones and other physiologically active compounds

It has recently been shown that endocrine cells of the gastrointestinal tract also synthesize thyroid-stimulating hormone and ACTH, i.e. hormones typical of the hypothalamus and pituitary gland, and pituitary cells - gastrin. Consequently, the hypothalamic-pituitary and gastrointestinal systems turned out to be related in some hormonal effects. There is also evidence that cells of the gastrointestinal tract secrete some steroid hormones.

For a long time, it was believed that the endocrine cells of the gastrointestinal tract secrete hormones and other physiologically active factors that participate primarily in the self-regulation of digestion and absorption of nutrients. However, it is now known that physiologically active substances control not only the functions of the digestive apparatus, but also the most important endocrine and metabolic functions of the entire body. It turned out that the so-called classical hormones of the gastrointestinal tract (secretin, gastrin, cholecystokinin) and a number of unidentified hypothetical hormones, in addition to local, or local, action, perform various functions in regulating other organs. Examples of hormones of general action are also somatostatin and areterin.

Disruption of the endogenous flow of physiologically active factors from the gastrointestinal tract to the internal environment of the body causes serious consequences. We have demonstrated that removal of even part of the endocrine system of the digestive apparatus under certain conditions leads either to death or to serious illness of the animal.

The exogenous flow of physiologically active substances consists mainly of specific substances formed during the breakdown of food. Thus, during the hydrolysis of milk and wheat proteins by pepsin, substances called exorphins are formed, i.e. natural morphine-like (in action) compounds. Under certain conditions, the resulting peptides can penetrate into the blood in certain quantities and participate in the modulation of the general hormonal background of the body. It can also be assumed that some peptides, including those formed during the normal digestion of certain food components, perform regulatory functions. Casomorphin, a product of the hydrolysis of milk protein (casein), belongs to such peptides.

The role of nutrition in the formation of human physiological and psychological standards is further increased by the discovery of the functions of some amino acids as neurotransmitters and their precursors.

Thus, nutrition is not the simple act of eating that can be reduced to enriching the body with nutrients. At the same time, there coexists a complex flow of hormonal factors that are extremely important, and perhaps even vital, for regulating food assimilation, metabolism, and, as has been discovered, some functions of the nervous system.

Bacterial metabolite fluxes

With the participation of the intestinal bacterial flora, three flows are formed, directed from the gastrointestinal tract into the internal environment of the body. One of them is the flow of nutrients modified by the microflora (for example, amines that arise during the decarboxylation of amino acids), the second is the flow of the products of the vital activity of the bacteria themselves, and the third is the flow of ballast substances modified by the bacterial flora. With the participation of the microflora, secondary nutrients are formed, including monosaccharides, volatile fatty acids, vitamins, essential amino acids, etc., substances that seem indifferent at the current level of knowledge, and toxic compounds. It was the presence of toxic compounds that gave rise to the idea of the advisability of suppressing the intestinal microflora, expressed by I. I. Mechnikov. However, it is possible that toxic substances, if their quantity does not exceed certain limits, are physiological and are constant and inevitable companions of exotrophy.

Some toxic substances, in particular toxic amines formed in the digestive system under the influence of bacterial flora, have long attracted attention. Among the amines with high physiological activity, cadaverine, histamine, octopamine, tyramine, pyrrolidine, piperidine, dimethylamine, etc. have been described. A certain idea of the content of these amines in the body is given by the level of their excretion with urine. Some of them significantly affect the state of the body. In various forms of diseases, in particular dysbacteriosis, the level of amines can increase sharply and be one of the causes of disruption of a number of body functions. The production of toxic amines can be suppressed by antibiotics.

Along with endogenous histamine, there is exogenous histamine, which is formed mainly in the intestine as a result of bacterial activity. Therefore, the use of antibiotics can lead to a number of shifts in the hormonal status of the body. It is possible that many pathological changes in the body are provoked not by the hyperfunction of the stomach cells secreting histamine, but due to its excessive production in the intestine by bacterial flora. Thus, with hyperproduction of histamine by the bacterial flora of the intestine, stomach ulcers, a tendency to disruption of the hypothalamic-pituitary functions, allergies, etc. appear.

The physiological importance of secondary nutrients is evidenced by the sharp increase in the need for vitamins in humans and animals whose bacterial flora is suppressed by antibiotics.

The transformation of ballast substances in the intestine occurs mainly under the influence of anaerobic microflora.

In addition to the flows listed, there is a flow of substances coming from food contaminated as a result of various industrial and agricultural technologies, or from a contaminated environment. This flow also includes xenobiotics.

It is now firmly established that dietary fiber plays a significant role in normalizing the activity of the gastrointestinal tract (especially the small and large intestines), increases the mass of the muscle layer, affects its motor activity, the rate of absorption of nutrients in the small intestine, the pressure in the cavity of the digestive apparatus, electrolyte metabolism in the body, the mass and electrolyte composition of feces, etc. It is important that dietary fiber has the ability to bind water and bile acids, as well as adsorb toxic compounds. The ability to bind water has a significant effect on the rate of transit of contents along the gastrointestinal tract. There is information in the literature that dietary fiber bran binds 5 times more water than its own weight, and fiber of vegetables such as carrots and turnips - 30 times more. Finally, dietary fiber affects the habitat of bacteria in the intestine and is one of the sources of nutrition for them. In particular, microorganisms use cellulose, hemicellulose and pectin, partially metabolizing them into acetic, propionic and butyric acids.

Dietary fiber is necessary for the normal functioning of not only the digestive system, but also the entire body. A number of disorders, including atherosclerosis, hypertension, ischemic heart disease, gastrointestinal pathology, diabetes, etc., in many cases are not only the result of excessive consumption of proteins and carbohydrates, but also the consequence of insufficient use of ballast substances. There is evidence that the lack of dietary fiber in the diet can provoke colon cancer. Without dietary fiber, the metabolism of not only bile acids, but also cholesterol and steroid hormones is disrupted. (It is amazing that Avicenna and his predecessors were already well aware of the harm of refined foods.)

Many forms of gastrointestinal tract and metabolic pathology can be prevented and treated by adding dietary fiber to the diet. Thus, these fibers can increase glucose tolerance and modify its absorption, which can be used to prevent and treat diabetes, hyperglycemia, and obesity. Increasing the amount of dietary fiber in the diet reduces blood cholesterol levels, which is due to the participation of fiber in the circulation of bile acids. The antitoxic effect of plant dietary fiber has also been shown. At the same time, when using a number of dietary fibers, the absorption of some microelements, especially zinc, is reduced.

Long-term use of dietary fiber reduces the severity of irritable bowel syndrome and diverticulosis of the colon. Dietary fiber helps successfully treat constipation, hemorrhoids, Crohn's disease and other gastrointestinal diseases, and can also serve as a preventive measure against relapses of gastric ulcer and duodenal ulcer. In particular, in chronic pancreatitis, a diet rich in fiber, i.e. dietary fiber, in most cases gives a positive therapeutic effect.

Therefore, it is necessary that the composition of food rations include not only proteins, fats, carbohydrates, microelements, vitamins, etc., but also dietary fiber, which is a valuable component of food.

Thus, on the basis of classical theory, attempts were made to create improved and enriched food by removing dietary fiber, which led to the development of many diseases, the so-called diseases of civilization. At present, the opposite direction is being intensively developed - searches are underway for adequate food rations that correspond to the needs of the body that arose in the course of evolution. In humans, such evolutionarily adequate food includes a significant proportion of substances that have long been unsuccessfully called ballast.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ], [ 8 ], [ 9 ], [ 10 ]