MUCOSAL BARRIER
Implications of a damaged mucosal barrier
A layer of epithelial cells forms the mucosal barrier. The cells form a barrier between the hostile external environment and the internal environment of the body. The epithelial cells are not an absolute barrier; the cells allow selective absorption of water and prevent the absorption of bacteria and toxins. Therefore, the mucosal barrier plays a vital role in the body by avoiding the re-absorption of harmful toxins as well as bacteria. When the mucosal barrier is damaged, it may lead to various implications including diarrhea.
The epithelial cells secrete mucus which gives the mucosal barrier its selective permeability function. Since it is selectively permeable, the mucosal barrier allows absorption of water, ions and small solutes. Defective mucus production can damage the mucosal barrier (Jerrold, 2009, 2). Excessive mucus production by the epithelial cells reduces the permeability of the mucosal barrier. As such, the barrier is unable to absorb ions and water back into the bloodstream. Also, defective mucus production leads to the formation of the unstirred layer (Jerrold, 2009, 2). The unstirred layer contributes to nutrients malabsorption by reducing the permeability of the mucosal barrier.
Tight junctions join the epithelial cells of the mucosal barrier ensure. The tight junction is a specialized connection between adjacent cells membranes which provide that there is no space between them, therefore, creating a barrier. During disease, changes to the components of the wall modify tight junction structure and function, which leads to barrier dysfunction (France et al., 2017). When the tight junction gets breached, the barrier becomes permeable and allows passage of microorganisms, antigens and other foreign proteins into the bloodstream. As such, damage to the tight junction can damage the mucosal barrier by increasing permeability.
When the mucosal barrier is damaged, pathogenic micro bacteria interact with the tight junction, and due to the increased permeability, they enter the bloodstream. Mucosal barrier damage leads to osmotic or malabsorptive diarrhea (Davidson et al., 2007, 5). The absorption of harmful bacteria due to increased permeability triggers an immune defense action from the body. The immune response causes inflammation in the surrounding tissues. The inflammation triggers with the tight function making it more porous. Excessive inflammation as the body triggers the defensive immune response causes abdominal pain and diarrhea. As permeability of the mucosal barrier increases, a rapid cell turnover takes place as the immune response gets triggered. The rapid cell turnover causes abdominal pain and diarrhea.
References
Davidson, G., Kritas, S. and Butler, R., 2007. Stressed mucosa. In Nutrition Support for Infants and Children at Risk (Vol. 59, pp. 133-146). Karger Publishers.
France, M.M. and Turner, J.R., 2017. The mucosal barrier at a glance. J Cell Sci, 130(2), pp.307-314.
Turner, J.R., 2009. Intestinal mucosal barrier function in health and disease. Nature reviews immunology, 9(11), p.799.