Retroperistalsis

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. Food then moves in the opposite direction, often from the duodenum into the stomach.

Retroperistalsis occurs pathologically during vomiting and physiologically at first part of duodenum where it protects from high acidity of food, and also at terminal ileum, where an amount of water and electrolyte is absorbed to assist defecation.

Peristalsis is the wormlike movement by which the alimentary canal or other tubular organs with both longitudinal and circular muscle fibers propel their contents, consisting of a wave of contraction passing along the tube. Increased peristalsis means faster movement of ingesta through the gut and less absorption of fluid, both tending to diarrhea. Reduced peristalsis means a longer alimentary sojourn, greater inspissation of ingesta and a tendency to constipation. See also peristaltic, paralytic ileus. Peristalsis, involuntary movements of the longitudinal and circular muscles, primarily in the digestive tract but occasionally in other hollow tubes of the body, that occur in progressive wavelike contractions. Peristaltic waves occur in the esophagus, stomach, and intestines. The waves can be short, local reflexes or long, continuous contractions that travel the whole length of the organ, depending upon their location and what initiates their action.

In the esophagus, peristaltic waves begin at the upper portion of the tube and travel the whole length, pushing food ahead of the wave into the stomach. Particles of food left behind in the esophagus initiate secondary peristaltic waves that remove leftover substances. One wave travels the full length of the tube in about nine seconds. The peristaltic-wave contractions in the esophagus of humans are weak compared with those of most other mammals. In cud-chewing animals, such as cows, reverse peristalsis can occur so that the food is brought back from the stomach to the mouth for rechewing.

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