Protective systems of the gastrointestinal tract

Last reviewed by: Aleksey Portnov , medical expert, on 01.06.2018

The theory of adequate nutrition attaches great importance to systems protecting the body from the penetration of various harmful substances into its internal environment. The intake of nutrients in the gastrointestinal tract should be considered not only as a way of replenishing energy and plastic materials, but also as an allergic and toxic aggression. Indeed, nutrition is associated with the danger of penetration into the internal environment of the body of various kinds of antigens and toxic substances. Only thanks to a complex system of protection, the negative aspects of nutrition are effectively neutralized.

First of all, we should note a system that is still referred to as mechanical, or passive. This means a limited permeability of the gastrointestinal mucosa for water-soluble molecules with a relatively small molecular weight (less than 300-500) and impermeability for polymers, including proteins, mucopolysaccharides and other substances with antigenic properties. However, for cells of the digestive apparatus during postnatal development, endocytosis is characteristic, which contributes to the introduction of macromolecules and foreign antigens into the internal environment of the organism. There are data that cells of the gastrointestinal tract of adult organisms are also capable of absorbing large molecules, including unsplit ones. Such processes are designated by Mr. Volkheimer as a perforation. In addition, when passing food through the gastrointestinal tract, a significant amount of volatile fatty acids is formed, some of which, when absorbed, cause a toxic effect, while others - a local irritant effect. As for xenobiotics, their formation and absorption in the gastrointestinal tract vary depending on the composition of the properties and the contamination of the food.

There are several other mechanisms that prevent the entry of toxic substances and antigens from the enteric environment into the internal environment, two of which are transformational ones. One such mechanism is associated with glycocalysis, which is impenetrable for many large molecules. Exceptions are molecules that undergo hydrolysis by enzymes (pancreatic amylase, lipase, proteases) adsorbed in glycocalyx structures. In this connection, the contact of allergic and toxic reactions of unsplit molecules with the cell membrane is hampered, and molecules undergoing hydrolysis lose their antigenic and toxic properties.

Another transformation mechanism is caused by enzyme systems localized on the apical membrane of intestinal cells and splitting oligomers up to monomers capable of absorption. Thus, the enzyme systems of glycocalyx and lipoprotein membrane serve as a barrier preventing the entry and contact of large molecules with the membrane of intestinal cells. An important role can play intracellular peptidases, considered by us as an additional barrier and as a mechanism of protection against physiologically active compounds.

To understand the mechanisms of protection, it is important that the human mucosa of the human small intestine contains more than 400,000 plasma cells per 1 mm. In addition, about 1 million lymphocytes were detected per 1 c m 2 of the intestinal mucosa. Normally, the jejunum contains 6 to 40 lymphocytes per 100 epithelial cells. This means that in the small intestine, in addition to the epithelial layer separating the enteral and internal environments of the body, there is still a powerful leukocyte layer.

The intestinal immune system is part of the body's immune system and consists of several different compartments. The lymphocytes of these compartments have many similarities with non-intestinal lymphocytes, but they also have unique features. In this case, populations of different lymphocytes of the small intestine interact due to migration of lymphocytes from one compartment to another.

The lymphatic tissue of the small intestine is about 25% of the entire intestinal mucosa. It is presented in the form of accumulations in Peyer's patches and lamina propria (individual lymph nodes), as well as a population of disseminated lymphocytes localized in the epithelium and lamina propria. The mucosa of the small intestine contains macrophages, T-, B- and M-lymphocytes, intraepithelial lymphocytes, target cells, etc.

Immune mechanisms can act in the cavity of the small intestine, on its surface and in the lamina propria. At the same time, intestinal lymphocytes can spread to other tissues and organs, including the mammary glands, female genital organs, lymphatic bronchial tissue, and participate in their immunity. Damage to the mechanisms that control the body's immunity and the immune sensitivity of the small intestine to antigens can make a difference in the pathogenesis of violations of the local immunity of the intestine and in the development of allergic reactions.

Non-immune and immune mechanisms to protect the small intestine protect it from foreign antigens.

Although the mucosa of the digestive tract potentially serves as an area through which antigens and toxic substances can penetrate into the internal environment of the body, an effective duplicate protection system, including both mechanical (passive) and active protection factors, operates here. In this case, the systems that produce antibodies and the cellular immunity system interact in the intestine. It should be added that the protective functions of the hepatic barrier, which realizes the absorption of toxic substances by means of cupfer cells, are supplemented by a system of antitoxic reactions in the epithelium of the small intestine.


The discovery of the general patterns of assimilation of nutrients equally valid for the most primitive and for the most highly developed organisms inevitably led to the formation of a new evolutionary reasoned theory suitable for the interpretation of the assimilatory processes not only of man but also of other groups of organisms. The theory of adequate nutrition proposed by us is not a modification of the classical, but a new theory with a different axiomatics. At the same time, one of the basic postulates of the classical theory, according to which the intake and expenditure in the body of nutrients must be balanced, the new theory entirely accepts.

According to the theory of balanced nutrition, food, which is a complex structure and consists of nutrients, ballast substances and in some cases toxic products, undergoes mechanical, physicochemical and, in particular, enzymatic processing. As a result, useful components of food are extracted and converted into species-specific compounds that are absorbed in the small intestine and provide energy and plastic needs of the body. (Many physiologists and biochemists compare this process with the extraction of valuable components from ore.) From the ballast substances, some elements of the digestive juices, dropped cells of the epithelial layer of the gastrointestinal tract, as well as a number of products of the vital activity of the bacterial flora, partially utilizing nutrients and ballast, secrets are formed , which are ejected from the body. From this scheme of food assimilation follow the principles of calculating the amount of nutrients that enter the body together with food, evaluate its merits, etc.

According to the theory, adequate nutrition, as well as the transition from a hungry state to a satisfied one, is caused not only by nutrients, but also by various vital regulatory compounds coming from the intestinal to the internal environment of the body. Such regulating compounds are primarily hormones produced by numerous endocrine cells of the gastrointestinal tract, which in number and variety exceed the entire endocrine system of the body. Regulatory compounds include also hormone-like factors, such as food derivatives, formed due to the action of enzymes on the digestive apparatus of the macroorganism and bacterial flora on it. In some cases, it is not possible to draw a clear line between regulatory and toxic substances, such as histamine.

From the point of view of the classical theory of feeding the microflora of the digestive system in monogastric organisms, including humans (but not ruminants), it is not even a neutral, but rather a harmful attribute. From the standpoint of the theory of adequate nutrition, the bacterial flora of the gastrointestinal tract, not only in ruminants, but also, apparently, in all or the vast majority of multicellular organisms is a necessary participant in assimilation of food. It has now been established that in the food activity of numerous organisms in the digestive system, not only does it extract some useful part of it - primary nutrients, but also the transformation of various food components under the influence of microflora, as well as the enrichment of its vital activity products. As a result, the unused portion of the nutrient becomes an active part of the enteric environment that possesses a number of important properties.

For complex organisms, it is fair to assume that in the metabolic sense they are superorganismic systems in which the host interacts with a specific microflora. Under the action of microflora, secondary nutrients are formed, which are extremely important, and in many cases necessary. The source of secondary nutrients are ballast nutrients involved in the regulation of many local functions of the body.

Assimilation of food, in accordance with the classical theory of nutrition, reduces to the enzymatic hydrolysis of its complex organic structures and the extraction of simple elements - the proper nutrients. Hence a number of fundamental ideas about the advisability of enriching food, that is, the separation of nutrient-containing components from ballast, as well as the use of ready-made nutrients as final products of cleavage, suited or even injected blood, etc. In contrast, according to the theory of adequate nutrition, there is not only the splitting of food, but also the preparation of nutrients and physiologically active substances as a result of exposure to the microflora of the gastrointestinal tract, per hour ballast substances. In this way, many vitamins, volatile fatty acids and the necessary essential amino acids are formed, which significantly affects the body's needs for food coming from outside. The ratio between primary and secondary nutrients can vary widely, depending on the species and even individual characteristics of the microflora. In addition, along with secondary nutrients under the influence of the bacterial flora, toxic substances are formed, in particular toxic amines. The activity of bacterial flora, which is an obligatory component of multicellular organisms, is closely related to a number of important features of the macroorganism.

As repeatedly noted, the development of the theory of adequate nutrition relies on general biological and evolutionary patterns, as well as on the achievements of a number of sciences, in particular biology, chemistry, physics and medicine. Indeed, for the biologist, not only the "formula", but also the technology of any process is extremely important, since evolution is in the direction of optimizing the technology of biological processes. In biological systems, much depends on the technology of processes, since their high efficiency, and sometimes the very possibility, is associated with the realization of certain intermediate links. Insufficient efficiency of their implementation or their interaction disrupts the functioning of the system as a whole. This presentation explains some fundamental differences between theories of balanced and adequate nutrition. The first theory, in essence, is determined by the balanced formula of nutrition, the second, besides such a formula, takes into account the technology of nutrition, that is, the technology of food assimilation processes by various groups of organisms.

Finally, the theory of adequate nutrition is one of the central elements of the interdisciplinary science of trophology. The unification of many sections of biological and medical sciences concerning various aspects of assimilation of food by biological systems of varying degrees of complexity (from the cell and the organism to the ecosystems and the biosphere) into one science is necessary for understanding the fundamental unity of nature. This is also important for characterizing the processes of interaction in the biosphere on the basis of trophic connections, that is, for considering the biosphere as a trophosphere. But in not less, and perhaps more, the formation of trophology, including the theory of adequate nutrition, is essential for various medical sciences, as trophism of tissues and its disorders, various problems of gastroenterology, theoretical and applied aspects of nutrition science is in fact, irrationally separated parts of one common problem - the problems of food assimilation by organisms standing at different levels of the evolutionary ladder. This problem should be considered from some unitary positions on the basis of broader and deeper than before views.

Thus, the theory of adequate nutrition is, so to speak, the theory of balanced nutrition, in which "biological wings" have grown. This means that the theory of adequate nutrition is applicable not only to a person or one particular group of animals, but also to a variety of animal species and, moreover, to all groups of organisms.

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