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A complicated act, usually initiated voluntarily but always completed reflexively, whereby food is moved from the mouth through the pharynx and esophagus to the stomach. It occurs in the following three stages.
SYN: SEE: deglutition
In the first stage, food is placed on the surface of the tongue. The tip of the tongue is placed against the hard palate; then elevation of the larynx and backward movement of the tongue forces food through the isthmus of the fauces in the pharynx.
In the second stage, the food passes through the pharynx. This involves constriction of the walls of the pharynx, backward bending of the epiglottis, and an upward and forward movement of the larynx and trachea. This may be observed externally with the bobbing of the Adam's apple. Food is kept from entering the nasal cavity by elevation of the soft palate and from entering the larynx by closure of the glottis and backward inclination of the epiglottis. During this stage, respiratory movements are inhibited by reflex.
In the third stage, food moves down the esophagus and into the stomach. This movement is accomplished by momentum from the second stage, peristaltic contractions, and gravity. With the body in an upright position, liquids pass rapidly and do not require assistance from the esophagus. However, second-stage momentum and peristaltic contractions are sufficient to allow liquids to be drunk even when the head is lower than the stomach.
Difficulty in swallowing is called dysphagia. SEE: dysphagia;