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Physiology of the Gastrointestinal Tract and Intestinal Microflora

At the level of the human gastrointestinal tract it colonizes a large population of microorganisms, the large intestine being by far the host of the highest bacterial density, with 10¹¹ to 10¹² CFU / gram. Advances in molecular biology in recent years have allowed a more detailed investigation of the intestinal microbiota, which has led to the description of this set of microorganisms as a true „forgotten organ” of our body.

A balanced intestinal flora is an important factor for our health. This flora is an ecosystem with almost 2 million genes, an ensemble called the microbiome, which numerically exceeds human genes, belonging to a number of over 300-500 bacterial species.

If, initially, it was thought that the flora is simply saprophytic and has no definite roles, research has shown that it is rather a symbiosis: by ensuring the nutrient substrate and the environment conducive to the development of bacteria, they contribute to the health of the human being in many ways. First, the microbiota plays an important role in digestion, maintaining the integrity of the intestinal epithelial barrier, and developing local immunity. Undigested or unabsorbed carbohydrates are broken down by bacterial enzymes, short-chain fatty acids are produced, which are used as an energy source for the colonic mucosa. Moreover, short-chain fatty acids contribute to the development of epithelial cells, their proliferation and differentiation.

The intestinal microbiota is a balanced ecosystem, but this balance can be disturbed by environmental factors. Microbiotic imbalance (or intestinal dysbiosis) is associated with unfavorable consequences for the host. The presence of high levels of pathogens (bacteria with unfavorable potential) can influence the disease state. The consequences of disturbing the intestinal flora are varied: after a long treatment with antibiotics, for example, the intestinal flora is partially destroyed, creating the opportunity to colonize with other pathogenic microorganisms (eg colitis with Clostridium difficile and necrotizing enterocolitis of the newborn or premature baby).

Irritable bowel syndrome is a common condition that involves problems with intestinal motility, visceral sensitivity, but also the intestinal microbiota. In patients with irritable bowel syndrome, quantitative and qualitative differences were found in the microbiota in the mucosa and in the feces, compared to healthy individuals.

„Bacterial overcrowding” is also a pathological condition. Abnormally high levels of microorganisms in the gut can cause diarrhea, discomfort, excess gas, abdominal pain.

Most bacteriological studies have shown the importance of intestinal dysbiosis in initiating and amplifying the inflammatory response characteristic of inflammatory bowel disease (IBD). In other cases, the permeability of the intestinal wall may increase in the context of pathologies or infectious processes, and the bacterial flora may translocate to the submucosal areas and, eventually, to the general circulation, producing a particularly severe septic damage. It seems that this is the mechanism that can influence various septic processes in seriously ill patients in ATI services.

According to recent research, qualitative changes in the intestinal flora have the potential to be implicated in a condition that can be called the disease of the 21st century: obesity.

It seems that the predominance in the intestinal flora of bacterial strains that can influence the level of absorbable nutrients may play an important role in the genesis and evolution of obesity.

Recent research also confirms the association between intestinal dysbiosis and type II diabetes and the potential for effective modulation of the intestinal microbiome in the control of this pathology. In children, the involvement of the microbiome in the development of allergies is recognized. The neonatal period and early childhood are ideal for a proper colonization of the intestinal microbiome, for the development of the immune system and to achieve a balance between tolerance and reactivity.

In this context, the concept of microbiota is a topical issue, analyzed in medical events and a research topic for practitioners around the world.

The development of the fields of molecular biology – genomics, metagenomics, metabolomics – offers new perspectives and ensures the detailed research of the involvement of the microbiota in the health of the host.