What is the mechanism of antiperistalsis that occurs during vomiting? Why the peristaltic waves normally don't propagate in anal to oral direction? Please give logical explanation with authentic sources. :)
Because of the mechanism of descending inhibition. Distension of the esophagus and intestine causes a reflex action that leads to circular muscular contraction just above the bolus/chymus. Longitudinal muscle also contracts (shortens) .