The small intestine: barrier, permeability and microbiota

In recent years, there has been growing interest in the comprehension of the physiology of intestinal permeability and mi-crobiota; and how these elements could influence the pathogenesis of diseases. The term intestinal permeability describes all the processes that allow the passage of molecules as water, electrolytes and nutrients through the intestinal barrier by the paracellular or the transcellular transport systems with several implications for self-tolerance and not-self immunity. An increased permeability might induce a more significant interaction of the immune system with unknown external an-tigens. This might favor the onset of several immune-related extra-intestinal diseases including coeliac disease, diabetes mellitus type 1, bronchial asthma and inflammatory bowel diseases. Furthermore, the intestinal permeability interacts every day with microbiota, the complex system of mutualistic inhabitants and commensal microorganisms living in the healthy gut. Microbiota is implicated in physiological functions by actively participating in digestion, absorption, synthesis of vitamins and protection from external aggressions. The critical site where these processes occur is the small intestine to which this updated review is dedicated. Understanding its anatomy, its barrier structure and permeability modulation and its microbiota composition is the essential skill to comprehend the complex pathogenesis of several -not only gastroenterological -diseases. (Cite this article as: Stalla FM, Astegiano M, Ribaldone DG, Saracco GM, Pellicano R. The small intestine: barrier, perme-ability and microbiota. Minerva Gastroenterol 2022;68:98-110. DOI: 10.23736/S2724-5985.20.02808-1)

Automated summary

In recent years, there has been increasing interest in understanding the physiology of intestinal permeability and microbiota and their influence on disease pathogenesis. Intestinal permeability refers to the processes that allow the passage of molecules such as water, electrolytes, and nutrients through the intestinal barrier, and it has implications for immune responses and the development of immune-related diseases. The intestinal permeability also interacts with the microbiota, which plays a crucial role in digestive and protective functions. This review focuses on the small intestine and its anatomy, barrier structure, permeability modulation, and microbiota composition, highlighting their importance in understanding the complex pathogenesis of various diseases, not limited to gastroenterological conditions.