Sphincter

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Sphincter
Identifiers
FMA75004
Anatomical terms of muscle

A sphincter is a circular

faeces.[2]

Functioning

Each sphincter is associated with the lumen (opening) it surrounds. As long as the sphincter muscle is contracted, its length is shortened and the lumen is constricted (closed). Relaxation of the muscle causes it to lengthen, opening the lumen and allowing the passage of liquids, solids, or gases.

This is evident, for example, in the

.

Many sphincters are used every day in the normal course of

acids
and other stomach contents from pushing up and into the oesophagus, but opens to let swallowed food pass into the stomach.

Classifications

Sphincters can be further classified into functional and anatomical sphincters:[citation needed]

  • Anatomical sphincters have a localised and often circular muscle thickening to facilitate their action as a sphincter.
  • Functional sphincters do not have this localised muscle thickening and achieve their sphincteric action through muscle contraction around (extrinsic) or within (intrinsic) the structure.

Sphincters can also be voluntarily or involuntarily controlled:

Examples

ileocaecal valve and sphincter

References

  1. ^ .
  2. ^ Emanuel, Linda L.; Ferris, Frank D.; von Gunten, Charles F.; Hauser, Joshua M.; Von Roenn, Jamie H. (February 11, 2010). "The Last Hours of Living: Practical Advice for Clinicians". Medscape.