Disorders of the Anal Sphincters

  • N. W. Read
  • Wei Ming Sun
Part of the Topics in Gastroenterology book series (TGEN)


The anal sphincter is really two sphincters in one. It consists of an inner ring of smooth muscle, which is contiguous with the smooth muscle of the rectum, and an outer striated muscle ring, which is linked functionally to the puborectalis fibers of the levator ani complex (Fig. 1). The internal sphincter (IAS) is not under conscious control, but like all other smooth muscle sphincters, relaxes when the bowel immediately proximal to it contracts or is distended. The external sphincter (EAS) and puborectalis are under conscious control and tend to contract together, increasing the sphincter resistance and accentuating the anorectal angulation.


Irritable Bowel Syndrome Pelvic Floor Anal Sphincter Anal Canal Internal Anal Sphincter 
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Copyright information

© Plenum Publishing Corporation 1989

Authors and Affiliations

  • N. W. Read
    • 1
  • Wei Ming Sun
    • 1
  1. 1.Department of Human Gastrointestinal Physiology and NutritionRoyal Hallamshire HospitalSheffieldEngland

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