Protective Effects of Gastric Mucus

The gastric mucosa is continuously exposed to many noxious factors and substances. How the gastric mucosa maintains structural integrity and resists auto-digestion by substances such as acid and pepsin puzzled clinicians and investigators for more than 200 years. The gastric epithelium must also resist damage from extrinsic agents, including Helicobacter pylori (H. pylori) and noxious ingestions such as ethanol and nonsteroidal anti-inflammatory drugs (NSAIDs). The luminal surface of the stomach is covered by a viscoelastic mucus gel layer that acts as a protective barrier against the harsh luminal environment. The structural characteristics of this barrier are primary indicators of its physiological function and changes of its composition have been identified in gastrointestinal pathologies. This chapter presents recent insights into the implication of the gastric mucus barrier as “no mucus, no protection”. While acid, pepsin, and H. pylori are thought to be major factors in the pathophysiology of gastritis, the importance of the mucosal defense system has also been emphasized. Gastric ‘cytoprotection’ refers to a reduction or prevention of chemically induced acute hemorrhagic erosions by compounds such as prostaglandin (PG) and SH derivatives without inhibiting acid secretion in rodents (Robert, 1979; Szabo et al., 1981). Since the concept of ‘cytoprotection’ was introduced, increasing attention has been paid to the effect of medications on the gastric mucosal defensive mechanisms. Although the exact mechanisms of the mucosal defense system are unknown, it involves one or more of the naturally occurring gastric mucosal defensive factors such as mucus metabolism. For estimation of the gastroprotective function, many drugs have been investigated for their activity to protect the gastric mucosa from a variety of necrotizing agents such as ethanol and HCl. Considerable information has accumulated about the gastroprotective function of the mucus that covers the mucosal surface of the stomach.