When food is not being ingested, both oesophageal sphincters remain closed. The presence of a bolus of food in the pharynx opens the upper oesophageal sphincter and allows the food to pass into the oesophagus. A peristaltic wave consists of a wave of contraction of the circular muscle, followed by a wave of relaxation. These waves of contraction pass along the walls of the oesophagus and move foodstuff towards the stomach. Each peristaltic wave takes about nine seconds to travel the length of the oesophagus. Therefore it is not primarily gravity, but peristalsis, that moves food towards the stomach, although gravity does assist the process. Secondary peristalsis, which arises from within the oesophagus, is controlled by sympathetic stimulation.
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