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How does peristalsis move food through the esophagus?

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Diagram of the human digestive system viewed from the front, showing and labeling organs including the mouth, teeth, tongue, salivary glands, pharynx, esophagus, liver, stomach, gallbladder, pancreas, large intestine, small intestine, appendix, rectum, and anus. — digestion The human digestive system as seen from the front.

Peristalsis is an involuntary, wavelike contraction of the circular and longitudinal muscles that moves food through the esophagus and into the stomach.1

The process functions through the following mechanisms:

Primary Peristaltic Contractions: These waves originate in the pharynx during the act of swallowing. The advancing wave creates a pressure gradient that sweeps the bolus ahead of it.2
Secondary Peristaltic Contractions: If a bolus is too large or the primary wave is too weak to move it effectively, local distension of the esophageal wall triggers secondary waves. These contractions originate around the bolus to propel it forward.2
Sphincter Coordination: As the bolus reaches the junction with the stomach, the lower esophageal sphincter relaxes, allowing the food to enter the stomach.2

While gravity can assist in moving liquids when a person is in an upright position, the high-pressure contractions of the peristaltic wave ensure that transport occurs regardless of body orientation.2