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The science of alcohol
The science of alcohol

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1.1 Absorption of ethanol from the gut into the bloodstream

The structure of the digestive tract is illustrated in Figure 1. When foods or drinks are swallowed, they pass from the mouth through the oesophagus into the stomach. Here they are mixed with acid and digestive enzymes and broken down into small fragments before passing into the small intestine through the pyloric sphincter.

The stomach is not very efficient at absorbing the molecules released from digested food and drink; instead these are mainly absorbed by the small intestine. Ethanol is therefore absorbed relatively slowly while it is in the stomach, and most (about 80%) is absorbed in the small intestine (Figure 1). Absorption of ethanol from the small intestine into the blood takes place by passive diffusion across the intestinal cell membranes.

An illustration of the digestive system.
Figure 1 A schematic diagram of the digestive tract and associated organs that make up the digestive system

If the stomach is empty, the pyloric sphincter, which sits between the stomach and the small intestine, will be open. Consequently, if someone drinks alcohol on an empty stomach the ethanol passes straight through the open pyloric sphincter into the small intestine and hence is absorbed more rapidly.

  • Would you expect the concentration of ethanol in the blood to rise more rapidly or more slowly if there is also food in the stomach?

  • You would expect the concentration of ethanol in the blood to rise more slowly when there is food in the stomach. This is because the pyloric sphincter would be closed, so the ethanol mixed with the food would only be gradually released into the small intestine. The ethanol trapped in the stomach is absorbed only very slowly.