Gastric Protection
The stomach does a very good job digesting the food that nourishes us, but remarkably, it also does a very good job not digesting itself. The reason for this is that there is a layer of mucus 0.5 -- 1.0 mm thick lining the wall of the stomach which affords this protection. The mechanism by which the mucus layer is formed and maintained, and the way in which mucus aids in protecting the stomach is not well understood. It is also not understood how acid can be secreted into the stomach with a pH of about 2, while maintaining a pH of about 7 next to the cell wall.
A proposition for how this might work has been suggested by Schreiber et al. They hypothesize that the mucus that is secreted from the base of the gastric pits acts as a buffer of hydrogen and as such transports secreted protons toward the lumen of the stomach, keeping the pH in the pit high. However, as the mucin approaches the lumen of the stomach, the pH lowers, catalyzing the pH dependent activation of pepsin (from pepsinogen), causing mucin to degrade and releasing the bound hydrogen into the lumen. (see the above figure.)
The overall goal of this project is to develop a model of the secretion, flow and degradation of mucin in the gastric pit, taking into account the important ions such as hydrogen, sodium, and as we know from our mucin secretion project , calcium, and other important chemicals including pepsin and bicarbonate, in order to gain an understanding of how the mucin layer is maintained and how it functions to provide acid protection and transport.
Publications on gastric protection
Frank Lynch and J. P. Keener, Transport of Gastric Juice Through the Gastric Mucus Layer, in preparation.
