Hereditary diseases of the digestive system
Digestion of complex food substances( polymers) is carried out in the cavity of the small intestine, where the initial stages of the cleavage of proteins, fats, carbohydrates and nucleic acids occur. This cavity digestion, in which the leading role is played by enzymes of the pancreas. The subsequent stages and stages of digestion are performed on the inner surface of the intestine - membranes of epithelial cells. This membrane, or pristenochnoe, digestion, occurring under the influence of intestinal enzymes, as well as enzymes of the pancreas. Spatially membrane digestion occupies an intermediate position between extracellular and intracellular digestion and is carried out by enzymes localized on the structures of the cell membrane.
Some diseases in the clinic are studied much better and more detailed. This applies primarily to the pathology of the cleavage. The pathology of absorption is less studied and therefore less frequently detected. This is not only about hereditary forms of malabsorption syndrome, but also about its secondary manifestations in various acquired digestive system diseases. Moreover, among the currently known diseases of cleavage, two main forms predominate-disaccharidase insufficiency and enterokinase deficiency. A sharp deficiency of digestive enzymes occurs in diseases such as celiac disease and cystic fibrosis. At the same time, impaired absorption is represented by a significantly wider range of diseases and includes, in addition to cystic fibrosis, malabsorption of various nutrients, impaired absorption of calcium and phosphorus, enteropathic acrodermatitis( a skin disease that develops against a background of digestive enzymes), congenital chloride diarrhea, secretory diarrhea, as well as many other diseases.
If we characterize the hereditary pathology of intestinal transport from molecular biological positions, we can say that this pathology is caused by gene mutations leading to the exclusion of the synthesis of specific vectors through the membranes of intestinal cells or to such changes in their structure that sharply impair the absorption of the corresponding compounds. Membrane digestion is carried out on the outer surface of intestinal cells, forming a brush border with the glycocalyx localized on the surface of the microvilli. Glycocalix is an education that plays an extremely important role in the functioning of the digestive system and the entire body as a whole.
Intestinal cell( enterocyte) has a cylindrical shape, somewhat widened in the upper( apical) part and covered with a plasma membrane. On the apical surface of each enterocyte is about 3-4 thousand microvilli, i.e. on 1 mm2 of the intestinal surface there are 50-200 million microvilli. It is estimated that due to microvilli the surface of the small intestine increases approximately 40 times. Such an increase in the intestinal surface facilitates the incorporation of a large number of different enzyme and transport proteins into the membrane.
Glycocalix is a component of the membrane and forms on the apical surface of the enterocytes a layer up to 0.1 μm in thickness. It provides not only the mechanical strength of the plasma membrane, but also represents a molecular "sieve" that transmits molecules depending on their size and charge, has a negative charge, is characterized by considerable hydrophilicity and gives the transport processes a selective character. Glycocalix is not only a functional and diffusion barrier that prevents the penetration of bacteria, but also a specific barrier that determines the permeability of nutrients. At the same time, the apical membrane due to glycocalysis is practically inaccessible for many high-molecular compounds. At the same time, glycocalyx is easily permeable to molecules of those nutrients for which there are corresponding enzymes in its space of
.Consequently, glycocalyx is a structure that can serve as a regulator of the activity of various enzymes and a regulator of the permeability of nutrients. Atrophy of glycocalyx can be the cause of the damaging effect of the toxic substances of the digestive lump on the membrane of the intestine. A characteristic feature of the glycocalyx of the brush border of the enterocytes is the high rate of its renewal. Rapid renewal of the glycocalyx ensures the efficient functioning of the brush border, since by the dropping of the "mature" glycocalyx, a peculiar effect of constant purification is created. Glycocalix is highly developed in the apical part of microvilli of intestinal cells.
In the glycocalysis, the fixed enzymes of the pancreas are mainly localized, as well as some others. These enzymes act on virtually all major types of nutrients.