The Digestive System and the Liver - Peristalsis



The mechanical action called peristalsis , affected by muscles in the walls of all the organs of the gastrointestinal tract, first comes into play in the esophagus. Two layers of muscles in-termesh in the intestinal walls: the inner layer encircles the esophagus in a series of rings; the outer layer stretches lengthwise along the tube. These two sets of muscles work in tandem to produce the basic action of persistalsis, called a peristaltic wave .

The alternative contraction and relaxation of the muscles—closing behind swallowed food and opening in front of it—combine to move both liquid and solid food (medical term, bolus ) along the digestive tract. Gravity, in a sense, is left behind once food enters the esophagus. Because of peristalsis, we can swallow lying down or even standing on our heads; and astronauts are able to eat in near zero-gravity or under weightless conditions.

Peristalsis has another important function besides moving food through the body. The constricting and relaxing muscles serve also to knead, churn, and pummel the solid remains of the food left after our teeth have done their best.



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