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The rectum is part of the distal part of the gastrointestinal tract; it is between the sigmoid colon and anus.


Pathologists generally agree that: the rectum starts/the sigmoid ends at the place where serosa ends on the posterior aspect of the bowel. In other words, the peritoneal reflection is the landmark that separates the sigmoid colon and rectum.

Notes on the definition

  • On a practical level, the (anatomic/pathologic) definition is not easy to apply from the lumen, i.e. the definition is not practical in the endoscopic context.
  • There are several definitions for the rectum.[1][2]
    • This is likely due to the above practical issue.


  • In a survey of surgeons:[2]
    • 67% defined it by an anatomical landmark
      • 35% of all respondents considered the peritoneal reflection the proximal boundary of the rectum.
    • 30% defined the proximal boundary as a distance from the anal verge.

See also


  1. Massalou D, Moszkowicz D, Mariage D, Baqué P, Camuzard O, Bronsard N (April 2018). "Is it possible to give a single definition of the rectosigmoid junction?". Surg Radiol Anat 40 (4): 431–438. doi:10.1007/s00276-017-1954-4. PMID 29218384.
  2. 2.0 2.1 Kenig, J.; Richter, P. (Sep 2013). "Definition of the rectum and level of the peritoneal reflection - still a matter of debate?". Wideochir Inne Tech Maloinwazyjne 8 (3): 183-6. doi:10.5114/wiitm.2011.34205. PMID 24130630.