Swallowing (deglutition) is initiated voluntarily. It is divided into three phases: buccal, pharyngeal, and esophageal. In the buccal phase, the tongue pushes the bolus against the soft palate and back of the mouth. The soft palate elevates to seal off the nasopharynx and the swallowing reflex is triggered in the medulla oblongata.
In the pharyngeal phase, breathing is inhibited in the brainstem respiratory center and the epiglottis closes to block the trachea. In the esophageal phase, food is propelled down the esophagus by peristalsis. In peristalsis, circular muscle in the esophageal wall contracts behind the bolus and relaxes in front of it. The lower esophageal sphincter is the entrance to the stomach. It closes once the bolus passes through.
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