Descending colon

The descending colon is the part of the large intestine that extends from the left colic (splenic) flexure to the sigmoid colon. It travels downward through the left hypochondriac and left lumbar regions of the abdomen along the lateral border of the left kidney. Near the lower end of the kidney, it curves medially towards the psoas major muscle and then descends between the psoas major and quadratus lumborum muscles to reach the iliac crest, where it continues as the sigmoid colon.

Anatomical relations of descending colon

The descending colon is usually secondarily retroperitoneal, meaning that it is fixed to the posterior abdominal wall. Its anterior and lateral surfaces are covered by peritoneum, while its posterior surface is attached by connective tissue to the posterior abdominal wall. Posteriorly, it is related to the lower and lateral part of the left kidney, the aponeurotic origin of the transversus abdominis, and the quadratus lumborum muscle. Anteriorly, it is crossed by loops of the small intestine.

Compared with the ascending colon, the descending colon is generally smaller in diameter, lies deeper within the abdomen. Like other parts of the colon, it possesses taeniae coli, haustra, and omental appendices.

Function

Its main functions are the absorption of water and electrolytes and the storage and propulsion of fecal material toward the sigmoid colon.