AskDefine | Define sphincter

Dictionary Definition

sphincter n : a ring of muscle that contracts to close an opening [syn: anatomical sphincter, sphincter muscle]

User Contributed Dictionary

English

Etymology

From late Latin sphincter, from Greek sphinkter, band, contractile muscle, from sphingein, to bind tight. Compare Sphinx, "the strangler".

Noun

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

Related terms

Translations

  • Czech: svěrač
  • Finnish: sulkijalihas
  • Greek: σφιγκτήρας (sfigktíras)

See also

Extensive Definition

A sphincter is a structure, usually a circular muscle, that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning. There are over 40 different sphincters in the human body; some of these sphincters are microscopic in size.
Many sphincters are used every day in the normal course of digestion. 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 use of the epiglottis is a typical example of an involuntary action by the body.

Examples of sphincters

Sphincters prove effective in the mediation of the entrance or release of liquids and fluids; this is evident in the blowholes of numerous marine mammals, for example.
Sphincters can also 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 also can be voluntarily or involuntarily controlled:
  • Voluntary sphincters are supplied by somatic nerves
  • Involuntary sphincters are stimulated by autonomic nerves
sphincter in Catalan: Esfínter
sphincter in German: Schließmuskel
sphincter in Spanish: Esfínter
sphincter in French: Sphincter
sphincter in Italian: Sfintere
sphincter in Kurdish: Miçînik
sphincter in Dutch: Sluitspier
sphincter in Japanese: 括約筋
sphincter in Korean: 괄약근
sphincter in Polish: Zwieracz
sphincter in Portuguese: Esfíncter

Synonyms, Antonyms and Related Words

O, annular muscle, annulus, areola, aureole, chaplet, circle, circuit, circumference, circus, closed circle, corona, coronet, crown, cycle, diadem, discus, disk, eternal return, fairy ring, garland, glory, halo, lasso, logical circle, loop, looplet, magic circle, noose, orbit, radius, ring, rondelle, round, roundel, saucer, vicious circle, wheel, wreath
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