Gastroduodenal mucus bicarbonate barrier: protection against acid and pepsin.

• Secretion of bicarbonate into the adherent layer of mucus gel creates a pH gradient with a near neutral pH at the epithelial surfaces in stomach and duodenum, providing the first line of mucosal protection against luminal acid. The continuous adherent mucus layer is also a barrier to luminal pepsin thereby protecting the underlying mucosa from proteolytic digestion. Here we review the current state of the gastroduodenal mucus bicarbonate barrier two decades later from when the first supporting experimental evidence appeared. The primary function of the adherent mucus gel layer is a structural one to create a stable unstirred layer to support surface neutralisation of acid and act as a protective physical barrier against luminal pepsin. The emphasis therefore on mucus in this review is on the form and role of the adherent mucus gel layer. The primary function of the mucosal bicarbonate secretion is to neutralise acid diffusing into the mucus gel layer and for there quantitatively to be sufficient secretion to maintain a near neutral pH at the mucus-mucosal surface interface. The emphasis on mucosal bicarbonate in this review is on the mechanisms and control of its secretion and the establishment of a surface pH gradient. Evidence suggests that under normal physiological conditions the mucus bicarbonate barrier is sufficient for protection of the gastric mucosa against acid and pepsin and, even more so, in the duodenum

Keyword

acid/base transporters

CFTR channel

surface pH gradient

mucus gels

trefoil peptides

Publication and Content Type

ref (subject category)

art (subject category)