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Belching (also known as burping, ructus, or eructation) is the release of gas from the digestive tract (mainly esophagus and stomach) through the mouth. It is usually accompanied with a typical sound and, at times, an odor.
Belching is generally caused by swallowing air when eating or drinking and subsequently expelling (or inhaling) it, so in this case the expelled gas is mainly a mixture of nitrogen and oxygen. Burps can also be caused by drinking carbonated drinks such as beer, soft drinks, energy drinks or champagne, in which case the expelled gas is primarily carbon dioxide from the drink itself. Common diabetes drugs metformin and Byetta can cause belching, especially at higher doses. This often resolves in a few weeks. Belching combined with other symptoms such as dyspepsia, nausea and heartburn may be a sign of an ulcer or hiatal hernia, and should be reviewed by a physician. Other causes of belching: food allergy, gallbladder problems, acid reflux disease, H. pylori, and gastritis.
The sound of burping is caused by the vibration of the upper esophageal sphincter as the gas passes through it. In microgravity environments, belching is normally associated with regurgitation. The valve at the top of the stomach (the gastroesophageal junction) does not produce a tight seal, and in the absence of gravity, the stomach contents tend to float near this loose seal, making them likely to come up along with the expelled air.
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Babies are particularly subject to accumulation of gas in the stomach while feeding, and this can cause considerable discomfort and agitation unless the child is burped. The act of burping an infant involves placing the child in a position conducive to gas expulsion (for example holding the infant up to the adult's shoulder, with the infant's stomach resting on the adult's chest) and then lightly patting the lower back so that the child burps. Because burping can cause vomiting in infants, a "burp cloth" or "burp pad" is sometimes employed on the shoulder to protect the adult's clothing.
In certain cultures, notably Chinese and Indian, belching, given appropriate contexts, are regarded as being acceptable. In Japan, belching during a meal is considered bad manners. In others, particularly Western cultures, such as North American, French, Italian, and British cultures, belching is deemed socially inappropriate.
Many other mammals, such as cattle, dogs, and sheep also belch. In the case of ruminants, the gas (wind) expelled is actually methane produced as a byproduct of the animal's digestive process. This methane is produced exclusively by a narrow cohert of methanogenic archaea produce this effect; Escherichia coli (E. coli) and other bacteria lack the enzymes and cofactors required for methane production. An average cow is thought to emit between 542 litres (if located in a barn) and 600 litres (if in a field) of methane per day through belching and exhalation, making commercially farmed cattle a major[quantify] contributor to the greenhouse effect. 95% of this gas (wind) is emitted through belching. This has led scientists at the Commonwealth Scientific and Industrial Research Organisation of Perth, Australia, to develop an anti-methanogen vaccine to minimize methane in cattle belchs.
One reason that domesticated cows belch so much is because they are often fed foods that their digestive systems do not process, such as corn and soy. Some farmers have reduced belching in their cows by feeding them alfalfa and flaxseed, which are closer to the grasses that they had eaten in the wild before they were domesticated.
In some animals, a failure to belch successfully can be fatal. This is particularly common among domesticated ruminants that are allowed to gorge themselves on very rich spring clover or alfalfa. The condition, known as bloat, is basically a high pressure buildup of gastric gases and requires immediate veterinary treatment, usually the insertion of a flexible rubber hose down the esophagus—or in extreme cases the lancing of the animal's side with a trochar and cannula—to expel the buildup of gas. Some fish are also known to expel air from their gills; here the belch is produced by gas being expelled from the gas bladder.