constrictor muscle
Quick Summary
A constrictor muscle is a ring-like muscle that contracts to close an opening or cavity in the body. These muscles are crucial for various bodily functions. For example, the sphincter pylori muscle controls the passage of food from the stomach to the small intestine. In excretion, the sphincter ani externus keeps the anal opening closed, and the sphincter urethrae provides voluntary control over urination. The eye also has a sphincter pupillae muscle within the iris that constricts the pupil in bright light. Smooth muscle, which is found in many internal organs, relies on its constrictive abilities for the proper functioning of systems like the cardiovascular and gastrointestinal tracts.1234
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