Rectum

Dr Henry Knipe et al.

The rectum is the last part of the large intestine. It is located within the pelvis and is the continuation of the sigmoid colon after the rectosigmoid junction and continues as the anal canal at the angle created by puborectalis

At the level of the S3 vertebral body, the sigmoid colon loses its mesentery and becomes the rectum. As the rectum passes in front of the sacrum, it takes an AP concave shape. It also is sinuous and takes on three bends when viewed anteriorly. The taenia coli also flatten and fuse to form an outer longitudinal muscular layer, thus the rectum does not have the distinctive haustra nor epiploic appendages that the rest of the large intestine has. The rectum is approximately 15 cm long. 

If demarcated from a purely gastrointestinal perspective, the rectum extends from rectosigmoid junction to proximal anorectal sphincter. Its upper third is covered by peritoneum anteriorly and laterally, mid third only anterior and its lower third is not covered.

The lower part of the rectum is dilated and is called the rectal ampulla and there are three semilunar transverse rectal folds (valves of Houston), which project into the rectum.

The rectum continues on as the anal canal at the level of the coccyx tip. It takes on an acute angle, the perineal flexure, as it passes through the puborectalis muscle and is the anal canal after this point. 

Relations
  • upper rectum: inferior mesenteric plexus
  • middle and lower rectum: superior and inferior hypogastric plexus

Lymphatics run with superior rectal vessels to the inferior mesenteric group to the drain the upper third. The lower two-thirds drain along the middle rectal vessels to the internal iliac group. 


Abdominal and pelvic anatomy
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Article Information

rID: 22765
Section: Anatomy
Synonyms or Alternate Spellings:
  • Rectal anatomy

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