The Anatomy of the Large Intestine

Abstract

The large intestine extends from the ileocaecal (ileocolic) junction, where it begins as the caecum, via the ascending, transverse, descending and sigmoid parts of the colon, rectum and anal canal, to the anal verge (the junction of perineal skin and anal mucosa at the anus). Understanding the basic stages in the development of the large intestine will help to explain its normal relationships to other abdominal and pelvic viscera and its peritoneal attachments and neurovascular supply; it will also aid in the interpretation of the presenting features of congenital large bowel disorders such as anorectal malformations and malrotation of the gut. The caecum, vermiform appendix, ascending colon and proximal two thirds of the transverse colon develop from the midgut, whereas the distal one third of the transverse colon, the descending colon, the sigmoid colon, the rectum and the proximal part of the anal canal develop from the hindgut. All are lined by endoderm and innervated by autonomic nerves. The distal part of the surgical anal canal is derived from the proctodaeal ectoderm and underlying mesenchyme and is innervated by spinal nerves. The line of union between the proximal and distal parts of the anal canal corresponds with the region of the anal valves.