Introduction | Anatomy | Abstracting, Coding, & Staging | Treatment | Hands-on Exercise |
Anatomy of Colon and Rectum
Anatomy of the Colon and Rectum | Layers of Bowel Wall | Regional Lymph Nodes | Unit Review & Quiz |

The entire colon is about 5 feet (150 cm) long, and is divided into five major segments. The rectum is the last anatomic segment before the anus.

The ascending and descending colon are supported by peritoneal folds called mesentery.

The right colon consists of the cecum, ascending colon, hepatic flexure and the right half of the transverse colon. The left colon consists of the left half of the transverse colon, splenic flexure, descending colon, and sigmoid. Click here to see Figure 1.

Parts of Colon and Rectum

Cecum (proximal right colon)--6 x 9 cm pouch covered with peritoneum
Appendix--a vermiform (wormlike) diverticulum located in the lower cecum
Ascending colon--20-25 cm long, located behind the peritoneum
Hepatic flexure--lies under right lobe of liver
Transverse colon--lies anterior in abdomen, attached to gastrocolic ligament
Splenic flexure--near tail of pancreas and spleen
Descending colon--10-15 cm long, located behind the peritoneum
Sigmoid colon--loop extending distally from border of left posterior major psoas muscle
Rectosigmoid segment--between 10 and 15 cm from anal verge
Rectum--12 cm long; upper third covered by peritoneum; no peritoneum on lower third which is also called
the rectal ampulla. About 10 cm of the rectum lies below the lower edge of the peritoneum (below the
peritoneal reflection), outside the peritoneal cavity.
Anal canal--most distal 4-5 cm to anal verge

Click here to see Figure 2.