The anal canal is the terminal part of the large intestine.

It is situated between the rectum and anus, below the level of the pelvic diaphragm. It lies in the anal triangle of perineum in between the right and left ischiorectal fossae.

In humans it is approximately 2.5 to 4 cm long, extending from the anorectal junction to the anus. It is directed downwards and backwards. It is surrounded by inner involuntary and outer voluntary sphincters which keep the lumen closed in the form of an anteroposterior slit.

It is differentiated from the rectum by the transition of the internal surface from endodermal to skinlike ectodermal tissue.

The anal canal is divided into two halves, upper and lower. The upper half has longitudinal folds or elevations of tunica mucosa. Its mucosa is lined by simple columnar epithelium. Its lower ends are joined together by folds of mucus membrane called anal valves. The upper half of the anal canal is supplied by the superior rectal artery which is a branch of the inferior mesenteric artery.

The lower half of the anal canal is lined by stratified squamous epithelium that blends with the skin.

A whitish line called Hilton's white line indicates the junction between simple columnar epithelium and stratified squamous epithelium.

Additional images

<gallery> Image:Anorectum.gif |Anatomy of the anus and rectum Image:Gray404.png|Left Levator ani from within. Image:Gray1080.png|The interior of the anal cami and lower part of the rectum. Image:Gray1228.png|Median sagittal section of male pelvis. Image:Gray1230.png|Median sagittal section of female pelvis. </gallery>

See also

• Anal columns
• Anal sinuses
• Anal valves
• Pectinate line
• anus

External links

• - "The rectum and anal canal in the male pelvis."

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