also called
deglutition, the act of passing food from the
mouth, by way of the
pharynx (or throat) and
esophagus, to the
stomach. Three stages are involved in swallowing food.
The first begins in the
mouth. There, food is mixed with
saliva for lubrication and placed on the back of the
tongue. The
mouth closes, and the soft portion of the roof of the mouth (
soft palate) rises so that the passageway between the
nasal and
oral cavities is closed off. The
tongue rolls backward, propelling food into the oral
pharynx, a chamber behind the mouth that functions to transport food and air.
Once food enters the
pharynx, the second stage of swallowing begins.
Respiration is temporarily inhibited as the
larynx, or
voice box, rises to close the
glottis (the opening to the air passage). Pressure within the
mouth and
pharynx pushes food toward the
esophagus. At the beginning of the
esophagus there is a muscular constrictor, the upper esophageal
sphincter, which relaxes and opens when food approaches. Food passes from the
pharynx into the
esophagus; the upper esophageal
sphincter then immediately closes, preventing flow of food back into the mouth.
Once food is in the esophagus, the final phase of swallowing begins. The larynx lowers, the glottis opens, and breathing resumes. From the time food leaves the mouth until it passes the upper sphincter, only about one second of time elapses, during which all these body mechanisms spontaneously occur. After passing the upper sphincter, movements in the esophagus carry food to the stomach. Rhythmic muscular contractions (peristaltic waves) and pressure within the esophagus push the food downward. Folds in the esophageal wall stretch out as materials pass by them and again contract once they have passed. At the lower end of the esophagus, the lower esophageal sphincter relaxes and food enters the stomach; the sphincter then closes again to prevent reflux of gastric juices and food materials.