The swallowing reflex is initiated by touch rceptors in the pharynx. This reflex involves a series of ordered and coordinated motor impulses to muscles of the pharynx, upper espohogeal sphincter, esophageal striated muscle, esophageal smooth muscle, and lower esophageal sphincter. The motor activity of the stomach mixes food with gastric juice and mechanically subdivides the food. Gastric emptying is closely regulated, which ensures that gastric contents are not emptied into the duodenum at a rate faster than the duodenum and jejunum can neutralize the gastric acid and process the chyme. Hormonal and neural mechanisms initiated by the presence of acid, fats, peptides, and hypertonicity in the duodenum regulate gastric emptying.
Segmentation is the major contractile activity in the small intestine.
Segmental contractions mix and circulate intestinal contents but are not very propulsive. The slow rate of transport of small intestinal contents allows adequate time for digension and absorption. The MMC is characterized by 75 to 90-minute periods of quiescsence interrupted by periods of vigorous and intensely propulsive contractions that last 3 to 6 minutes. The contractile phase of the MMC begins in the stomach and appears to propagate along the entire length of the small intestine. The MMC sweeps the stomach and the small intestine clear of any debris that remains from the previous meal.