The tutor discusses the use of sphincters in the digestive system.

A sphincter is a ring of muscle that, when tightened, can restrict passage between two areas. The digestive system uses them at either end of the stomach. At the front end, the cardiac sphincter keeps acidified food from spilling back up. At the exit, the pyloric sphincter controls the entry of acidified food into the duodenum. Its release is coordinated with the arrival of pancreatic juice, which contains sodium bicarbonate to neutralize the acid.

The anal sphincter, which controls the exit of feces from the body, is perhaps a familiar example of one.

Source:

Mader, Sylvia S. Inquiry into Life, 9th ed. Toronto: McGraw-Hill, 2000.

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