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The gastric mucosal barrier is an example of superb natural engineering. It has to withstand a most hostile chemical environment of highly acidic and proteolytic gastric juice which rapidly kills swallowed microorganisms and breaks down ingested foodstuffs. Despite the gastric mucosa being composed of similar organic molecules to microorganisms and food it is undamaged by the highly corrosive juice which it secretes.
Most epithelial surfaces exposed to a harsh environment protect themselves by means of a multilayered squamous epithelium such as that of the mouth or oesophagus, or by keratinised squamous epithelium such as the skin. Despite the gastric mucosa having to withstand a far harsher chemical environment than any of the above, it consists of only a simple columnar epithelium. It is chilling to think that it is only a single epithelial cell which separates us from our highly corrosive gastric juice. Squamous epithelium may be likened to an old-fashioned battleship protected by thick armour plating. In contrast, the gastric epithelium is more like a modern warship with a light thin hull but highly sophisticated defence systems.
Most of the human gastric mucosa has glands containing parietal cells and it is this acid secreting mucosa which has the most elegant means of protection from the acid it secretes. Such is the effectiveness of this protective system that even Helicobacter pylori infection rarely causes ulceration in the acid secreting region of the stomach. Ulcers usually occur in non-acid secreting mucosa such as the duodenum, pre-pyloric region, or on areas of gastric intestinal metaplasia where the parietal cells have undergone atrophy.1
The first line of defence is the unstirred layer of mucus lining the epithelial surface and gastric pits. …