BIOLOGY Volume 1 - A Guide to General Biology - 2004

8. HETEROTROPHIC NUTRITION

8.3. The Human Alimentary Canal

8.3.5. Peristalsis

The food bolus is propelled along the alimentary tract As a result of Muscle contractions within the outer muscular coat of the gut wall. This coat consists of an outer longitudinal and an inner circular muscle layer (Fig. 8.12). Behind the food bolus, the circular Muscles contract, constricting the lumen of the gut, while ahead of the bolus, the longitudinal muscles contract, shortening and widening that section of the alimentary canal; as a result, the food is pushed forward (Fig. 8.18). This process is known as rhythmic segmentation.

In The Stomach and Small Intestine, another type of movement is possible: pendular movements, in which the walls of these Regions of the digestive tube abruptly and rapidly shorten, tossing the food from one wall to the other and thereby thoroughly mixing it. Strictly speaking, this type of movement is not considered peristaltic. The alimentary tract contracts simultaneously in several places (segmental movements).

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Fig. 8.18. A. Diagram of peristaltic movements in the Esophagus. B. X-ray of the human esophagus. The patient has previously swallowed a barium meal, which is opaque to X-rays. The Muscles of the esophageal section located above the barium meal contract and propel it toward the intestines.