The rectum is the final part of the large intestine and a continuation of the sigmoid colon. The rectum extends between the rectosigmoid junction and the anal canal and is typically 10 to 12 cm in length.

It has several bends or flexures: sacral, anorectal, and lateral flexures. The rectum ends with a dilated ampulla. The superior third of the rectum lies mesoperitoneally (it is covered by the peritoneum from the anterior aspect and both lateral sides), the middle third is retroperitoneal (covered by the peritoneum only from the anterior side), and the lower third is extraperitoneal (is not associated with the peritoneum).

The typical characteristics of the large intestine, such as taenia coli and haustra, are not found in the rectum.

Functionally, the rectum is involved in the temporary storage of the feces and defecation.

The anal canal is the continuation of the rectum and the final part of the gastrointestinal tract. It extends from the anorectal junction to the anus, and its length is 3 to 4 cm. The anal canal lies completely extraperitoneal.

This canal can be subdivided into three zones:

Columnar zone - in this zone, the mucous membrane forms folds (anal columns), which are produced by arterial cavernous bodies (anal cushions) in the submucosa; anal columns are interconnected at their distal ends by transverse folds (anal valves); behind the anal valves lie crypts of Morgagni into which the excretory of the anal glands open; all anal valves form the dentate line where the intestinal mucosa ends, and the squamous epithelium begins;
Intermediate zone - about 1 cm long zone distally from the dentate line that is lined by anal mucosa;
Cutaneous zone - the zone below the anal verge (anocutaneous line) located between the internal and external anal sphincter and covered by perianal skin.

The anal canal has an important role in defecation and maintaining fecal continence. It is surrounded by a muscular sphincter system that tightly closes the lumen.

Unlock with Premium

Rectum and anal canal