Alcohol's role in gastrointestinal tract disorders

Abstract

When alcohol is consumed, the alcoholic beverages first pass through the various segments of the gastrointestinal (GI) tract. Accordingly, alcohol may interfere with the structure as well as the function of GI-tract segments. For example, alcohol can impair the function of the muscles separating the esophagus from the stomach, thereby favoring the occurrence of heartburn. Alcohol-induced damage to the mucosal lining of the esophagus also increases the risk of esophageal cancer. In the stomach, alcohol interferes with gastric acid secretion and with the activity of the muscles surrounding the stomach. Similarly, alcohol may impair the muscle movement in the small and large intestines, contributing to the diarrhea frequently observed in alcoholics. Moreover, alcohol inhibits the absorption of nutrients in the small intestine and increases the transport of toxins across the intestinal walls, effects that may contribute to the development of alcohol-related damage to the liver and other organs.

The pathway of alcohol metabolism. Once in the liver, alcohol is converted into acetaldehyde, and the acetaldehyde is converted into acetate. The enzyme alcohol dehydrogenase (ADH) assists the chemical reaction in (i.e., catalyzes) the first half of alcohol metabolism, and the enzyme aldehyde dehydrogenase (ALDH) catalyzes the second half. NAD⁺ is a coenzyme that plays an accessory role in enzyme catalysis.

Figure 1

Schematic representation of the human gastrointestinal tract. The small intestine comprises the duodenum, the ileum, and the jejunum.

Figure 2

Schematic illustration of the villi lining the small intestine. These villi serve to increase the internal surface area of the intestine and thus enhance the absorption of nutrients.

Figure 3

Schematic presentation of the possible causes and consequences of mucosal injury, increased permeability of the intestinal mucosa to macromolecules, and bacterial overgrowth in the small intestine of chronic alcohol abusers. Thickness of arrows indicates strength of association between phenomena. (For definitions, see glossary, pp. 93–96.)