Anorectal Anatomy and Physiology

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The Rectum

The rectum and anal canal comprise the last portion of the large intestine. The rectum is located in the pelvis, begins at the level of the sacral promontory, and extends 12 to 18 cm distally. This portion of the enteric tract differs from the colon, and its beginning can be marked by noting where the adventitial taeniae bands have coalesced to form outer longitudinal muscle. The rectum has 2 or 3 curves within its lumen, created by submucosal folds called the valves of Houston. The peritoneum

Anal Continence

Anal continence is very complex, and investigation continues to further elucidate its mechanism. Several types of studies can be used to evaluate anorectal function, including anorectal manometry, electromyography, defecography, nerve stimulation testing, and radiographic studies, including endorectal ultrasound and magnetic resonance imaging (MRI).

Anal continence relies upon the ability of the anorectum to discriminate between the states of fecal matter, solid, liquid, or gas. Its presence

Physiologic testing

Multiple techniques have been developed to assess the physiologic function of the pelvic floor, rectum, and sphincters. In conjunction with a detailed history and physical exam, these techniques should be used to assess and detail function, identify and locate a lesion, or solidify a diagnosis.

Summary

The anorectal area consists of a relatively small but complex region where multiple anatomic and physiologic interactions occur to help aid continence and defecation. A thorough understanding of the anatomy and the available testing modalities is imperative to diagnose and treat the wide range of pathologic conditions that may occur.

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