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Flatulence Physiology

By Dr Ananya Mandal, MD

Flatulence is a normal biological process referring to the release of flatus or gas from the digestive system via the back passage.

Causes of flatulence

Aerophagia or swallowing air

When a person ingests food or water, they also swallow small amounts of air. This air accumulates within the gut and passes into the small intestine, the rectum and finally out of the body via the anus.

Carbohydrate intake

Many of the foods we eat are carbohydrates, which contain complex sugars and plant cellulose. Some of these carbohydrates cannot be digested and absorbed by the body and are therefore passed down the intestine into the colon where they form the bulk of a stool. These are called unabsorbable carbohydrates. Such carbohydrates may undergo fermentation by bacteria in the intestine, which gives rise to gases that then get trapped in the abdomen and are passed as wind via the anus. Some examples of common foods that can cause this type of gas and flatulence include broccoli, beans, cabbage, cauliflower, pulses, lentils, raisins, prunes, applies, onions and brussel sprouts. Drinks with sorbitol (such as sugar-free products) can also lead to excessive flatulence.

Mechanism of flatulence

Sensory nerve endings present in the rectum and anal canal can detect pressure exerted by the bulk of a stool. As this pressure mounts, a person feels the urgency to pass the stool. The flatus that gathers in the lower intestine and colon also exerts pressure and triggers a need to pass wind.

Flatulence often makes a sound, as the flatus passes through the tight anal sphincter. The speed the gas is passed at, the tightness of the sphincter and other factors such as water and body fat content, determine the type and pitch of the sound. Flatulence can occur accidentally when pressure within the abdomen is suddenly raised due to coughing, sneezing, sexual intercourse or laughing, for example.

Components of the flatus

The flatus is mainly composed of nitrogen, hydrogen and carbon dioxide. The carbon dioxide content is higher among people who drink carbonated beverages regularly. The flatulence is usually only foul smelling when it contains gases that smell such as sulphur, although it is normal for the flatus to smell a bit.

Reviewed by , BSc

Further Reading

Last Updated: Jul 2, 2014

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