Gas in the body

QUESTION : How is gas formed inside the human body?

R. P. Rammohan, Hyderabad

ANSWER : In human body gases can enter the gastrointestinal tract from three different sources: (1) swallowed air, (2) gases formed as a result of bacterial action, and (3) gases that diffuse from the blood into the gastrointestinal tract.

Most of the gases in the stomach are nitrogen and oxygen derived from swallowed air. In a normal person belching expels most of these gases.

Small intestine usually contains only small amounts of gas. Much of these is air that passes from the stomach into intestinal tract. In addition, considerable amount of carbon dioxide is also found. It is because of the reaction between acidic gastric juice and bicarbonate in pancreatic juice. Usually the liberated carbon dioxide in this reaction is absorbed through the intestinal mucosa. But sometimes it is too rapid that it cannot be fully absorbed. In such condition it begins to accumulate in the small intestine.

The large intestine contains varying amounts of oxygen, nitrogen, carbon dioxide, methane, and hydrogen. Among these oxygen and nitrogen are derived from swallowed air. The other gases, which occupy greater proportion, are derived from bacterial action. When the methane and hydrogen become suitable mixed with oxygen from swallowed air, an actual explosive mixture is occasionally formed.

Certain foods like cluster beans, cabbage, onion, cauliflower and corn are known to cause expultion of flatus through the anus. Some foods contain unabsorbed fermentable types of carbohydrates, which serve as a suitable medium for gas forming bacteria. When irritant foods, such as vinegar, irritate the large intestine excess gas results. This irritation also promotes rapid peristaltic expulsion of the gases before they can be absorbed.

The amount of gases entering or forming in the large intestine each day averages 7-10 litres. Whereas the average amount of gases expelled through the anus is usually only about 0.6 litres. The remainder is absorbed through the intestianal mucosa.

S. Palaniappan, Pudukkottai, T. N.

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