sphincter

(noun)

a ringlike band of muscle that surrounds a bodily opening, constricting and relaxing as required for normal physiological functioning

Related Terms

Examples of sphincter in the following topics:

  • Blood Flow Through the Body

    • The blood entering some capillary beds is controlled by small muscles called precapillary sphincters .
    • A sphincter is a ringlike band of muscle that surrounds a bodily opening, constricting and relaxing as required for normal physiological functioning.
    • If the precapillary sphincters are open, the blood will flow into the associated branches of the capillary bed.
    • If all of the sphincters are closed, then the blood will flow directly from the arteriole to the venule through the thoroughfare channel.
    • (a) Precapillary sphincters are rings of smooth muscle that regulate the flow of blood through capillaries; they help control the blood flow to where it is needed.

  • Digestive System: Small and Large Intestines

    • The "C-shaped," fixed part of the small intestine, the duodenum, is separated from the stomach by the pyloric sphincter which opens to allow chyme to move from the stomach to the duodenum where it mixes with pancreatic juices.
    • Two sphincters between the rectum and anus control elimination: the inner sphincter is involuntary, while the outer sphincter is voluntary.

  • Digestive System: Mouth and Stomach

    • The movement of chyme from the stomach into the small intestine is regulated by the pyloric sphincter.