Final answer:
The descending colon begins at the left colic flexure, descends vertically, and ends at the sigmoid colon. It is part of the large intestine, transitions from the retroperitoneal descending colon to the sigmoid colon which is tethered to the posterior abdominal wall by the mesocolon.
Step-by-step explanation:
The descending colon originates at the left colic flexure (also known as the splenic flexure) and descends vertically until it terminates at the sigmoid colon. The cecum marks the beginning of the colon and after the food residue has moved up the ascending colon and across the transverse colon, it reaches the left colic flexure. This point is located immediately inferior to the spleen. From the left colic flexure, the descending colon runs downwards along the left side of the posterior abdominal wall. It ultimately reaches the pelvis, where it transitions into the S-shaped sigmoid colon, which extends toward the midline of the body. Both the ascending and descending colon, along with the rectum, are located retroperitoneally. The mesocolon tethers the transverse and sigmoid colon to the posterior abdominal wall.