Figure 5.

Components of the physiological gut barrier. The number of microorganisms inhabiting the gastro-intestinal tract has been estimated to exceed 10¹⁴. Starting from the gut lumen, we observe microbes (1) in the most superficial layer of the mucous (2). The functional barrier (3) includes the role of gastrointestinal motility ad secretion of gastric acid and bile the epithelial barrier (4) is composed by the collection of gut cells and tight junctions. The immunological barrier (5) includes antimicrobial peptides, toll-like receptors, microbial- (MAMPs) and pathogen- (PAMPs) associated molecular patterns, and B/T lymphocytes. The gut vascular barrier (6) and the ultimate liver barrier (7) are depicted, as well. Adapted from Nicoletti et al. [91].