Colon Anatomy and Development

Colon Structure

• The colon is approximately 150 cm in length, starting from the ileocecal junction.
• The cecum and proximal transverse colon develop from the midgut, while the distal third of the transverse, descending, and sigmoid colon and the rectum are hindgut structures.

Comparing Colon and Small Bowel

• The colon differs from the small bowel in five key ways: caliber, degree of fixation, appendices epiploicae, teniae coli, and haustra.

Colon Diameter

• The diameter of the colon is variable, with the cecum having an average diameter of 7.5 cm and the sigmoid colon having an average diameter of 2.5 cm.

Colon Fixation

• A considerable amount of the colon is retroperitoneal and fixed along the posterior abdominal sidewall.

Appendices Epiploicae

• The colon has small fat tags on the serosal surface called appendices epiploicae, which are absent on the cecum, appendix, and rectum.

Teniae Coli

• The entire colon has three distinct longitudinal bands known as teniae coli, which are the condensation of the longitudinal muscle fibers in the outer layer of the bowel wall.
• The teniae coli converge at the appendix and at the rectum, making these structures void of teniae.

Haustra

• The colon has outpouchings of bowel wall between the tenia coli called haustra.

Colon Layers

• The bowel wall of the colon has the same layers as those of the small intestine: mucosa, submucosa, muscularis, and serosa.

Histologic Difference

• The major histologic difference between the colon and small intestine is that the colon has no villi (i.e., mucosal crypts of Lieberkühn), resulting in a more uniform surface with less absorptive area.