Flatulence

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]

Flatulence is the presence of a mixture of gases known as flatus in the digestive tract of mammals expelled from the rectum. It is more commonly known as ‘farting‘, ‘passing gas’, or ‘passing wind’ (UK).

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]

Flatus is expelled under pressure through the anus, whereby, as a result of the voluntary or involuntary tensing of the anal sphincter, the rapid evacuation of gases from the lower intestine occurs. Depending upon the relative state of the sphincter (relaxed/tense) and the positions of the buttocks, this often results in an audible crackling or trumpeting sound, but gas can also be passed quietly. The olfactory components of flatulence include skatole, indole, and sulfurous compounds.^[1] The non-odorous gases are mainly nitrogen (ingested), carbon dioxide (produced by aerobic microbes or ingested), and hydrogen(produced by some microbes and consumed by others), as well as lesser amounts of oxygen (ingested) and methane (produced by anaerobic microbes).^[2] Odors result from trace amounts of other components (often containing sulfurcompounds, see below).

Flatus is expelled under pressure through the anus, whereby, as a result of the voluntary or involuntary tensing of the anal sphincter, the rapid evacuation ofgases from the lower intestine occurs. Depending upon the relative state of the sphincter (relaxed/tense) and the positions of the buttocks, this often results in an audible crackling or trumpeting sound, but gas can also be passed quietly. The olfactory components of flatulence include skatole, indole, and sulfurous compounds.^[3] The non-odorous gases are mainly nitrogen (ingested), carbon dioxide (produced by aerobic microbes or ingested), and hydrogen(produced by some microbes and consumed by others), as well as lesser amounts of oxygen (ingested) and methane (produced by anaerobic microbes).^[4] Odors result from trace amounts of other components (often containing sulfurcompounds, see below).

Nitrogen is the primary gas released. Carbon dioxide is often present, especially in persons who drink carbonated beverages in quantity. Methane andhydrogen, lesser components, are flammable, and so flatus is susceptible to catching fire. Not all humans produce flatus that contains methane. For example, in one study of the feces of nine adults, only five of the samples contained bacteria capable of producing methane.^[5]Similar results are found in samples of gas obtained from within the rectum.

The gas released during a flatus event frequently has a foul odor which mainly results from low molecular weight fatty acids such as butyric acid(rancid butter smell) and reduced sulfur compounds such as hydrogen sulfide (rotten egg smell) and carbonyl sulfide that are the result of protein breakdown. The incidence of odoriferous compounds in flatus increases from herbivores, such as cattle, through omnivores to carnivorousspecies, such as cats or dogs. Flatulence odor can also be caused by the presence of large numbers of microflora bacteria and/or the presence of feces in therectum.

The major components of the flatus by percentage are:^[6]

• Nitrogen – 20% – 90%
• Hydrogen – 0% – 50%
• Carbon Dioxide – 10% – 30%
• Oxygen – 0% – 10%
• Methane – 0% – 10%

The noises commonly associated with flatulence are caused by the vibration of the anal sphincter, and not by the buttocks. The sound varies depending on the tightness of the sphincter muscle and velocity of the gas being propelled, as well as other factors such as water and body fat. The auditory pitch (sound) of the flatulence outburst can also be affected by the anal embouchure. Among humans, farting sometimes happens accidentally, such as incidentally to coughing or sneezing; on other occasions, farting can be voluntarily elicited by tensing the rectum or “bearing down” and subsequently releasing the anal sphincter. Humans are also known to flatulate during sleep, largely due to the relaxed state of body muscles, which results in the average person flatulating about 10-20 times through any given night.

Flatus is brought to the rectum via peristalsis, which also causes feces to descend from the large intestine, and may cause a similar feeling of urgency and discomfort. Nerve endings in the rectum usually enable individuals to distinguish between flatus and feces, although loose stool can confuse the individual, occasionally resulting in accidental defecation.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Carlos A Lopez, M.D. [2]

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

• Acetaminophen
• Albuterol
• Biliary disease
• Caffeine
• Cystic fibrosis
• Clostridium difficile
• Diverticulitis
• Lisinopril
• Irritable bowel syndrome
• Intermittent bowel obstruction
• Malabsorption
• Obesity

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