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internal anal sphincter

 

Definition: a smooth muscle ring, formed by an increase of the circular muscle fibers of the rectum, situated at the upper end of the anal canal, internal to the outer voluntary external anal sphincter. This sphincter is maximally contracted when the rectal ampulla is “at rest”—empty or relaxed to accommodate a distending fecal mass. It is inhibited with filling of the ampulla, increased distension, and peristalsis.

Synonym(s): musculus sphincter ani internusTA, internal sphincter muscle of anus

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

© Copyright 2018 Wolters Kluwer. All Rights Reserved. Review date: Sep 19, 2016.

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