The absorption of alcohol in the mouth and oesophagus is minimal because of the rapid passage of the alcohol through these structures; approximately 20% of ingested alcohol is absorbed in the stomach and the rest is absorbed in the small intestine.
Depending on the volume of alcohol ingested, a small quantity may reach the colon and be absorbed there.
Factors affecting the Rate of Absorption
There are a variety of factors which affect the rate at which alcohol is absorbed, and consequently, the rapidity with which the blood alcohol concentration rises:
- If the mucous membrane of the stomach or small intestine is covered by mucus or food, absorption is delayed as the surface area of contact between the alcohol and the mucous membrane has been decreased.
- If the blood supply to the mucous membrane is increased as a result of congestion, inflammation or the ingestion of warm liquids, absorption will be increased.
- The rate of absorption of alcohol depends on the concentration gradient between the alcohol in the stomach and small intestine and the alcohol in the blood of the capillaries in the stomach and intestinal wall; the smaller the gradient, the slower the absorption.
- Absorption of alcohol in the small intestine may be decreased if gastric motility is reduced by medicines such as sympathomimetics, very high alcohol concentrations or in cases of nausea and shock.
- Gastric motility and associated alcohol absorption is increased by the intake of large volumes of food and liquids.
- Gastric motility is increased in persons with gastritis and peptic ulceration.
- The presence of irritating substances in the stomach may cause pyloric sphincter contraction and a delay in gastric emptying, thereby delaying alcohol absorption.
- Psychological factors may unpredictably affect pyloric sphincter function and consequent alcohol absorption in the small intestine.
- Certain surgical procedures such as gastrectomy or gastro-jejunostomy will accelerate the passage of gastric contents into the small intestine with more rapid absorption of alcohol.
- The higher the alcohol content of a beverage, the slower the absorption rate because of secretion of excessive mucus, pyloric sphincter spasm and suppression of gastric motility.
- Large volumes of beverage make contact with a large surface area of mucous membrane and also increase gastric motility with resultant faster absorption of alcohol.
- The presence of carbohydrates in beer delays alcohol absorption.
- Alcohol absorption is accelerated where beverages contain gas such as carbon dioxide.
- Warm beverages are absorbed faster than cold ones with faster alcohol absorption.
- Foodstuffs which are fatty in nature or which have a high protein or carbohydrate content delay alcohol absorption by reducing contact between the alcohol and the mucous membranes.
- Fatty foods also delay gastric emptying with associated retardation of alcohol absorption in the small intestine.
- Parasympathetic agents such as carbachol, pilocarpine, atropine and belladona increase gastric motility and relaxation of the pyloric sphincter, thereby increasing alcohol absorption in the small intestine.
- Ingestion of levulose, nicotine and caffeine delay alcohol absorption.
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