Anal sphincter
Updates to Article Attributes
Body
was changed:
The anal sphincter is divided into an internal and external anal sphincter. It surrounds the anal canal.
Gross anatomy
Internal anal sphincter
- continuation of inner rectal muscle
- thickened, circular muscle fibres, up to 5 mm thick
- composed of visceral muscle
External anal sphincter
Composed of skeletal muscle and classically categorised into deep, superficial, and subcutaneous parts:
-
deep part
- circular muscle fibres
- blends with puborectalis part of levator ani (posteriorly and laterally)
- the aforementioned region is called the anorectal ring and is palpable on rectal examination
-
superficial part
- elliptical muscle fibres
- attaches from the tip of the coccyx posteriorly to the perineal body anteriorly
- only part of the sphincter with bony attachment
-
subcutaneous part
- circular muscle fibres
- lower ends curve inwards, lying below the end of the internal sphincter, the intersphincteric groove that results is palpable on examination
Related pathology
-<li>blends with puborectalis part of <a href="/articles/levator-ani-1">levator ani </a>(posteriorly and laterally)</li>- +<li>blends with puborectalis part of <a href="/articles/levator-ani-muscle">levator ani </a>(posteriorly and laterally)</li>
-</ul>- +</ul><h4>Related pathology</h4><ul><li><a title="perianal fistula" href="/articles/perianal-fistula">perianal fistula</a></li></ul>
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