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A time-space diagram of a peristaltic wave after a water swallow. High-pressure values are red, zero pressure is blue-green. The ridge in the upper part of the picture is the high pressure of the upper esophageal sphincter which only opens for a short time to let water pass.
Retroperistalsis is the reverse of the involuntary smooth muscle contractions of peristalsis.It usually occurs as a precursor to vomiting.Local irritation of the stomach, such as bacteria or food poisoning, activates the emetic center of the brain which in turn signals an imminent vomiting reflex.