A sphincter is an anatomical structure, or a circular muscle, that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning. Sphincters are found in many animals; there are over 50 in the human body, some microscopically small, in particular the precapillary sphincters.[1]



Sphincters prove effective in the mediation of the entrance or release of liquids and fluids; this is evident, for example, in the blowholes of numerous marine mammals.

Many sphincters are used every day in the normal course of digestion and vision. For example, the epiglottis is used to seal off the windpipe when swallowing, so as to ensure that no food or liquid enters the lungs. The function of the epiglottis is a typical example of an involuntary action by the body.


Sphincters can be further classified into functional and anatomical sphincters:

  • 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 indirectly through muscle contraction around (extrinsic) or within (intrinsic) the structure.

Sphincters can also be voluntarily or involuntarily controlled:

Examples of sphincters

Diagram of Ileocaecal valve and sphincter


  1. ^ a b Vander, Arthur; Sherman, James; & Luciano, Dorothy (1994). Human Physiology: The Mechanism of Body Function (Sixth Edition, International Edition). McGraw Hill, Inc. pp. 437–440. ISBN 0-07113761-0. 

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  • sphincter — [ sfɛ̃ktɛr ] n. m. • 1548; mot lat. d o. gr. ♦ Muscle annulaire disposé autour d un orifice naturel qu il resserre et ferme en se contractant. Sphincter de l anus; sphincter anal, vaginal. ● sphincter nom masculin (bas latin sphincter, du grec… …   Encyclopédie Universelle

  • Sphincter — Sphinc ter, a. (Anat.) Of, pertaining to, or designating, a sphincter; as, a sphincter muscle. [1913 Webster] …   The Collaborative International Dictionary of English

  • sphincter — 1570s, from M.Fr. sphincter, from L.L. sphincter contractile muscle, from Gk. sphinkter band, anything that binds tight, from sphingein to squeeze, bind, of unknown origin. First used in anatomical sense by Galen …   Etymology dictionary

  • Sphincter — Sphinc ter, n. [NL., fr. ??? to bind tight.] (Anat.) A muscle which surrounds, and by its contraction tends to close, a natural opening; as, the sphincter of the bladder. [1913 Webster] …   The Collaborative International Dictionary of English

  • Sphincter — (gr.), der Schließmuskel, s.d …   Pierer's Universal-Lexikon

  • sphincter — ► NOUN Anatomy ▪ a ring of muscle surrounding and serving to guard or close an opening such as the anus. ORIGIN Greek sphinkt r, from sphingein bind tight …   English terms dictionary

  • sphincter — [sfiŋk′tər] n. [LL < Gr sphinktēr < sphingein, to draw close < IE * spheig < base * spēi , to flourish, grow thick > SPEED, SPARE] Anat. a ring shaped muscle that surrounds a natural opening in the body and can open or close it by… …   English World dictionary

  • sphincter — A muscle that encircles a duct, tube, or orifice in such a way that its contraction constricts the lumen or orifice. SYN: musculus s. [TA], s. muscle [TA]. [G. sphinkter, a band or lace] s. of ampulla s. of hepatopancreatic ampulla. anatomic s.… …   Medical dictionary

  • Sphincter — Als Schließmuskel bezeichnet man in der Biologie einen Muskel, der ein Gehäuse o.ä. verschließt. So zieht der Schließmuskel der Muscheln die beiden Schalenhälften zusammen. In der Anatomie der Wirbeltiere ist ein Schließmuskel (griech. Sphinkter) …   Deutsch Wikipedia

  • Sphincter — Un sphincter est un muscle circulaire situé autour d’un conduit naturel (tube digestif, vessie, etc.). Sa contraction permet de fermer totalement ou partiellement un orifice ou un conduit du corps. Sa commande peut être volontaire ou automatique… …   Wikipédia en Français

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