Anal sphincter
Citation, DOI, disclosures and article data
At the time the article was created Aaron Wong had no recorded disclosures.
View Aaron Wong's current disclosuresAt the time the article was last revised Khalid Alhusseiny had no financial relationships to ineligible companies to disclose.
View Khalid Alhusseiny's current disclosures- Internal anal sphincter
- Anal sphincters
- Anal sphincter complex
- External anal sphincter
The anal sphincter is divided into internal and external anal sphincters. It surrounds the anal canal.
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Gross anatomy
Internal anal sphincter
continuous with the inner circular layer of rectal smooth muscle
thickened, circular fibers, up to 5 mm thick
External anal sphincter
Composed of skeletal muscle and classically categorized into deep, superficial, and subcutaneous parts:
-
deep part
circular muscle fibers
blends with puborectalis part of levator ani (posteriorly and laterally)
this region is called the anorectal ring and is palpable on rectal examination
-
superficial part
elliptical muscle fibers
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 fibers
-
lower ends curve inwards, lying below the end of the internal sphincter
the intersphincteric groove that results is palpable on examination
Innervation
internal anal sphincter: parasympathetic and sympathetic fibers from the superior and inferior hypogastric plexus
external anal sphincter: somatic fibers from the pudendal nerve (inferior rectal and deep perineal branches)
Related pathology
References
- 1. McMINN. Lasts Anatomy Regional and Applied. CHURCHILL LIVINGSTONE. (2003) ISBN:B0084AQDG8. Read it at Google Books - Find it at Amazon
- 2. Dobben A, Felt-Bersma R, ten Kate F, Stoker J. Cross-Sectional Imaging of the Anal Sphincter in Fecal Incontinence. AJR Am J Roentgenol. 2008;190(3):671-82. doi:10.2214/AJR.07.2920 - Pubmed
- 3. Rociu E, Stoker J, Eijkemans M, Laméris J. Normal Anal Sphincter Anatomy and Age- and Sex-Related Variations at High-Spatial-Resolution Endoanal MR Imaging. Radiology. 2000;217(2):395-401. doi:10.1148/radiology.217.2.r00nv13395 - Pubmed
- 4. Abdool Z, Sultan A, Thakar R. Ultrasound Imaging of the Anal Sphincter Complex: A Review. Br J Radiol. 2012;85(1015):865-75. doi:10.1259/bjr/27314678 - Pubmed
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