cabbagehead
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Between your stomach and esophagus is a valved called the upper esophageal sphincter. This valve (hopefully) keeps stomach acid from reaching the esophagus. Normally it only opens to let food pass through. However, if air gets in the stomach it can create discomfort. The sphincter can loosen enough to let some of this air out in a maneuver called an eructation. You and I call this a burp. Adults have enough control of the sphincter to belch when needed, but babies need a little help.
Patting a baby on the back helps move the air bubbles around enough to dislodge them from the stomach and esophagus. Since control of the sphincter is tenuous a little food gets carried along with the air. This is why babies spit up when they belch.
Adults don't normally eat or drink fast enough to get air in our stomachs, so belching is usually limited to times when we drink carbon dioxide-releasing foods like soda and beer. Babies, on the other hand, will drink milk from a bottle as fast as possible, resulting in some air intake. Nursing is done with the bottle pointed downwards to keep milk coming through the nipple instead of air.
 Posted 5299 day ago
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