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<unk>  lumen and blood. The barrier formed by the<unk>  epithelium separates the external environment (the contents of the<unk>  lumen) from the body and is the most extensive and important mucosal surface of body. However, the<unk>  mucin can also be barriers for the host antimicrobial peptides, thus plays a bidirectional barrier for host-microbial interaction. The<unk>  epithelium 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<unk>  lumen. Selective permeability is mediated via two major routes: *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 transport through the spaces that exist between epithelial cells. It is regulated by cellular junctions that are localized in the laminal membranes of the cells. This is the main route of passive flow of water and solutes across the<unk>  epithelium. Regulation depends on the intercellular tight junctions which have the most influence on paracellular transport. Disruption of the tight junction barrier can be a trigger for the development of<unk>  diseases.
Intestinal permeability
Vascular permeability
Digestion
Vasoactivity
Enterohepatic circulation
Muscle tone
Enteroenteric circulation
Indigestion