E. Engel et al., BARRIER FUNCTION OF THE GASTRIC MUCUS GEL, American journal of physiology: Gastrointestinal and liver physiology, 32(6), 1995, pp. 994-999
The gastric epithelium is covered by a continuous layer of secreted mu
cus and bicarbonate. The function of this mucobicarbonate layer in ter
ms of protecting the epithelial cells from luminal acid is controversi
al. Several studies conducted in vitro have shown that gastric mucus c
an slow proton diffusion and can enable the formation of a pH gradient
across the mucobicarbonate layer. In our laboratory, simultaneous mea
surements of intracellular pH and the thickness of the mucus gel overl
ying gastric surface cells in vivo indicated that surface cell acidifi
cation rates and mucus gel thickness were inversely related. This sugg
ests that the gastric mucobicarbonate layer delays proton permeation i
nto gastric surface cells, enabling secreted bicarbonate to neutralize
luminal acid. Several theoretical models, including the effects of mu
cus and bicarbonate secretion, convection, stirring, and Lipids are of
fered as a possible explanation for the experimental observations. Lip
id content and additional unstirred layers outside of the mucus gel ar
e offered as possible explanations for the experimental observations.
On the basis of the available data and theoretical considerations, we
can conclude that all of these factors probably interact in an integra
ted manner to protect the gastric epithelial cells from damage due to
luminal acid.