Expansion
Mucus and bicarbonate layer, tight junctions, rapid turnover and good blood flow
Expansion
Components of the barrier:
- Mucus layer: an unstirred gel about 200 micrometres thick
- Bicarbonate secretion into the mucus, keeping the epithelial surface at pH 7 while the lumen is at pH 2
- Tight junctions and an apical membrane impermeable to hydrogen ions
- Rapid epithelial turnover, every 3 to 5 days
- Rich mucosal blood flow, removing back-diffused acid and delivering bicarbonate
- Prostaglandins, which stimulate mucus and bicarbonate, promote blood flow and inhibit acid
Barrier failure:
- NSAIDs inhibit prostaglandin synthesis, removing several defences at once
- Helicobacter pylori produces urease and cytotoxins, causing inflammation; antral infection increases gastrin and acid, favouring duodenal ulcers, while body infection causes atrophy and reduced acid, favouring gastric ulcer and cancer
- Alcohol, bile reflux, ischaemia and stress damage the barrier directly
This framework explains treatment: acid suppression, eradication of the organism, and prostaglandin analogues such as misoprostol for NSAID users.