The colon is the part of the large intestine extending between the cecum and rectum. It consists of four parts: ascending, transverse, descending, and sigmoid.

Its ascending and descending portions are mesoperitoneal, while the transverse and sigmoid parts lie intraperitoneally.

Among the main functions of the colon is fluid and electrolyte reabsorption. In addition, the gut microflora located in the colon generates energy through a process called fermentation.

The ascending colon begins in the right iliac fossa, passes through the right flank and into the right hypochondriac region. It ends at the right colic (hepatic) flexure, which marks the junction of the ascending and transverse colon. The ascending colon lies mesoperitoneally, and it is connected to the posterior abdominal wall by the Toldt’s fascia. Between the ascending colon and the lateral part of the abdominal wall lies a deep vertical groove or recess called the right paracolic gutter. The ascending colon is actively involved in fluid and electrolyte reabsorption, gradually forming fecal matter.

The transverse colon is the part of the colon between the right and left colic flexures, extending through the right hypochondriac, epigastric, and left hypochondriac regions of the abdomen. It lies intraperitoneally. Superior to the transverse colon is the greater curvature of the stomach and the gastrocolic ligament. The greater omentum hangs over and extends inferiorly to the transverse colon. The transverse colon is attached to the posterior wall of the omental bursa via the transverse mesocolon - a peritoneal mesentery. This attachment forms two abdominal compartments called supracolic and infracolic compartments. The left colic flexure is located at the junction of the transverse and descending colon and lies just below the spleen. This bend is more acute, higher, and more posterior than the right colic flexure. The left colic flexure is attached to the diaphragm by the phrenicocolic ligament.

The descending part of the colon extends between the left colic flexure and the sigmoid colon. It spans the left hypochondriac region, left flank, and left iliac fossa. Located between the descending colon and the lateral part of the abdominal wall is the left paracolic gutter. The descending colon is located mesoperitoneally and is attached to the posterior abdominal wall via the Toldt's fascia.

The sigmoid colon is S-shaped and is the final segment of the colon. It begins above the pelvic inlet, passing from the left iliac fossa to the second/third sacral vertebra. Here the rectosigmoid junction marks the part where the sigmoid colon ends and the rectum begins. The sigmoid colon is intraperitoneal and is connected to the pelvic wall by the sigmoid mesocolon.

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Colon