MadSci Network: Biochemistry

Re: What kind of gas do you fart out?

Date: Tue Sep 23 12:08:18 2003
Posted By: Steve Mack, Post-doc/Fellow, Molecular and Cell Biology
Area of science: Biochemistry
ID: 1064273654.Bc

The medical/scientific term for a fart is flatus, the release of accumulated gastrointestinal gas through the anus. Gastrointestinal gas is a heterogeneous mixture of gasses that have been swallowed and which have passed through the digestive system, gasses that have been released from the bloodstream into the intestine, gasses that have been generated by the interaction of internal fluids, and gasses that have been generated in the intestine by the action of microorganisms.

The exact makeup of this mixture will vary from person to person, depending on what they eat, and how they eat it. For example, you will have a much higher chance of swallowing air if you chew with your mouth open. There may also be a genetic component that contributes to the composition of gastrointestinal gas.

In general, the major components of gastrointestinal gas are Nitrogen (N2), Carbon Dioxide (CO2), Oxygen (O2), Hydrogen (H2) and Methane (CH4). These five gasses represent 99% of the gastrointestinal gasses. Nitrogen is poorly absorbed from the digestive system, and is usually present in proportion to the ammount of atmospheric gas that has been swallowed. Oxygen can pass through the intestinal walls, so the portion of Oxygen will decrease in proportion to the ammount of time that the gas remains in the intestine. Carbon Dioxide can be swallowed, released into the intestine from the body, generated through the interaction of stomach acid with intestinal fluids, and generated by micro-organisms in the intestines. Hydrogen and Methan are also generated by intestinal micro-organisms.

The odors associated with flatus come from some of the compounds that represent the final 1%. These are usually sulfur compounds (e.g., Hydrogen Sulfide) and some nitrogenous compounds (e.g., indoles and skatoles). So, if you eat foods that are rich in sulfur, like eggs and meat, you will produce more bad-smelling gastrointestinal gas.

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