Peristalsis in the Digestive System
Peristaltic waves are produced by contractions of smooth muscles. One set of smooth muscles contract behind the chewed food to keep it from moving back into the mouth. Another set of smooth muscles then pushes the food forward along the digestive tract.
The process looks much like an earthworm propelling itself along through the ground. It also looks like an ocean wave traveling through the muscle. The muscle contracts creating a narrowing that slowly moves down the length esophagus, or other part of the digestive tract. These waves of narrowing muscle push the food and fluid in front of them as they move along. A wave pushing food along the esophagus takes about 8 to 9 seconds to travel from the mouth to the stomach.
In the esophagus, the waves only occur when there is food being swallowed. A single wave may be enough to push the food into the stomach. However, in the small intestines, the peristaltic waves are more continuous. Since the stomach only releases food into the small intestine in little spurts, the waves must repeat over and over again until all of the food is released from the stomach and is moved along the small intestine into the large intestine.
Peristaltic waves in the large intestine occur only one to three times per day. They help to propel feces along the large intestine, through the colon, to the rectum for expulsion from the body.