Federal government websites often end in. Before sharing sensitive information, make sure you're on a federal government site. The site is secure. NCBI Bookshelf. Abdelwahab Ahmed ; Tafline C. Arbor ; Waqar A. Authors Abdelwahab Ahmed 1 ; Tafline C. Arbor 2 ; Waqar A. Qureshi 3. The anal canal is the terminal part of the gastrointestinal tract that conveys material from the rectum to the anus. While it is typically around 2. The anal canal plays a vital role as a defense against organisms that might enter the body, it differentiates between solid, liquid, and gas, and it contributes to fecal continence.
Often not evaluated in the absence of symptoms, pathologies of the anal canal may be treated with wide-ranging measures as conservative as a sitz bath to as significant as surgical resection or radiation. The anal canal serves as a channel connecting the rectum to the end of the gastrointestinal system, the anus.
It is located within the anal triangle of the perineum and in between the fat-filled and wedge-shaped ischioanal, or ischiorectal, fossae that accommodate its expansion for the passage of fecal material. The transition from the rectum to the anus can be identified by the anorectal junction, or anorectal ring, which appears as a bend in the gastrointestinal tract and is supported by the puborectalis muscular sling. The anorectal junction is also the site where muscular fibers of its two sphincters blend superiorly with those of the puborectalis muscle.
The two functionally and anatomically distinct sphincters surrounding the anal canal are the internal anal sphincter and the external anal sphincter. Its function is dependent on the integrity of the rectoanal inhibitory reflex RAIR , which involves the reflexive relaxation of the internal anal sphincter in the presence of rectal distension.
It maintains a resting pressure in the absence of rectal distension. Thus, the internal anal sphincter's resting pressure is widely used as a direct measure of its functionality and is often assessed when evaluating a variety of pathologies. The external anal sphincter EAS is under voluntary control. The external anal sphincter maintains its tone to keep the orifice of the anal canal closed and relaxes upon defecation.
