The intestinal system
Why do we need a gut barrier? The intestinal barrier covers a surface of about 400 m2 and requires approximately 40% of the body’s energy expenditure. It prevents against loss of water and electrolytes and entry of antigens and microorganisms into the blodstream and body, while allowing exchange of molecules between the intestine and the rest of the body and allowing absorption from the intestine to the blodsteram of nutrients in the diet. Approximately 80 per cent of our immune system is attached to the gut, and it may therefore be relevant to think of bowel and intestinal flora in the development of autoimmune diseases, just as reactions to food or toxic substances may play a role in the development of diseases. The intestine plays a vital role in our health and in maintaining it.
It is the key organ of the immunity of the digestive tract but also of our overall immune defense. It is also thanks to it, that the nutrients necessary for the functioning of our organism are absorbed and redistributed where our organism demands it.
The barrier formed by the intestinal cells separates the external environment (the contents of the intestinal lumen) from the body and is the most extensive and important mucosal surface of the body, primary consisting of lactic acid bacteria ("Good bacteria"). The intestinal epithelium (coated with villi and microvilli) is composed is composed of a single layer of cells and serves two crucial functions. First, it acts as a barrier, preventing the entry of harmful substances such as foreign antigens, toxins and microorganisms. Second, it acts as a selective filter which facilitates the uptake of dietary nutrients, electrolytes, water and various other beneficial substances from the intestinal lumen. Selective permeability is mediated via two major routes:
Scheme of selective permeability routes of epithelial cells (red arrows). The transcellular (through the cells) and paracellular (between the cells) routes control the passage of substances between the intestinal lumen and blood.
- Transepithelial or transcellular permeability. This consists of specific transport of solutes across the epithelial cells. It is predominantly regulated by the activities of specialised transporters that translocate specific electrolytes, amino acids, sugars, short chain fatty acids and other molecules into or out of the cell.
- Paracellular Permeability: It depends on the transport through the spaces that exist between the epithelial cells. It is regulated by cellular compounds located in the laminal membranes of the cells. This is the main route of passive water flow and solutes through the intestinal epithelium. Regulation depends on intractable tight junctions, which most affect paracellular transport.
The destruction of the tight junction barrier can be a trigger for the development of bowel disease.