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Colon

Colon

For medical students2 min readUpdated 2026-10-10

The colon is an extended segment of the large intestine that topographically forms a frame surrounding the loops of the small intestine. Anatomically, it is divided into four consecutive parts, each with specific features of fixation to the posterior abdominal wall.

RegionsIncludes the ascending, transverse, descending, and sigmoid parts.
MobilityThe transverse and sigmoid sections possess their own mesentery and are highly mobile.
Sigmoid LengthAverages 54–55 cm, though subject to significant individual variations.
Lower BoundaryTransitions into the rectum strictly at the level of the third sacral vertebra.

General Topography

The colon (colon) is located in the abdominal cavity and lesser pelvis. Its main topographical feature is the formation of a frame surrounding the loops of the small intestine.

Depending on the direction of its course and location, four parts are distinguished:

Right Half of the Colon

The ascending colon begins at the cecum. It is localized in the right part of the abdominal cavity, ascending up to the level of the right hypochondrium. Its posterior surface is adjacent to the posterior abdominal wall, as it is located retroperitoneally. In the right hypochondrium, the colon bends to form the right colic flexure (flexura coli dextra) and continues into the next segment.

The transverse colon begins at the right flexure and courses to the left, ending at the left colic flexure (flexura coli sinistra). It lies in the upper floor of the abdominal cavity, with its projection typically corresponding to the cartilage of the 10th rib. Unlike the ascending part, it is covered by peritoneum on all sides (intraperitoneally) and has its own mesentery — mesocolon transversum. The presence of a mesentery provides this segment with considerable anatomical mobility.

Left Half and Transition to the Lesser Pelvis

The descending colon begins at the flexura coli sinistra and descends along the left side of the abdominal cavity to the level of the iliac crest. Like the ascending part, it is firmly fixed, lies retroperitoneally, and contacts the posterior abdominal wall with its posterior surface.

The sigmoid colon is located in the left iliac fossa, from where it descends into the lesser pelvis cavity. Its length averages 54–55 cm, though this parameter can vary widely among individuals. The sigmoid colon, similar to the transverse colon, is completely covered by peritoneum and has a mesentery (mesocolon sigmoideum), which accounts for its high degree of mobility. The colon terminates by transitioning into the rectum; this transition is projected at the level of the third sacral vertebra.

Mnemonic

To remember segment mobility: 'vertical' parts (ascending and descending) are fixed retroperitoneally and immobile, while 'horizontal/tortuous' parts (transverse and sigmoid) possess a mesentery and are freely movable.

Frequently asked questions

Where topographically is the left colic flexure (flexura coli sinistra) located?

The left colic flexure (flexura coli sinistra) is located in the left hypochondrium at the level of the 9th rib cartilage or the 8th intercostal space. Topographically, it lies approximately 4 cm higher and deeper (dorsally) than the right colic flexure. Superiorly, the flexure approaches the inferior pole of the spleen, and posteriorly it abuts the left kidney, separated from it by peritoneum and retroperitoneal adipose tissue.

What external anatomical features (surface structures) distinguish the colon from the small intestine?

The colon is distinguished from the small intestine by a larger diameter, a grayish-ash color, and the presence of specific structures on its external surface.

External anatomical features include:

  • Teniae coli (teniae coli) — three longitudinal bands of the outer muscular layer (tenia libera, tenia mesocolica, tenia omentalis).
  • Haustra (haustrae coli) — characteristic transverse sacculations of the wall between the teniae.
  • Epiploic appendices (appendices epiploicae / omentales) — pouches of the serous coat containing adipose tissue.
Which arteries supply the ascending and transverse colon?

The ascending and transverse colon are supplied by branches of the superior mesenteric artery.

  • Right colic artery (a. colica dextra) runs toward the middle section of the ascending colon; its ascending branch heads toward the right colic flexure and anastomoses with the middle colic artery.
  • Middle colic artery (a. colica media) runs into the mesentery of the transverse colon and divides into right and left branches. The right branch anastomoses with the a. colica dextra and supplies the right flexure and right half of the transverse colon; the left branch runs to the left half of the transverse colon and anastomoses with the a. colica sinistra.
Into which vein does venous drainage from the descending and sigmoid colon empty?

Venous drainage from the descending and sigmoid colon empties into the inferior mesenteric vein (v. mesenterica inferior).

This venous collecting system receives:

  • Left colic vein (v. colica sinistra) — drains blood from the descending colon.
  • Sigmoidal veins (vv. sigmoideae) — collect blood from the wall of the sigmoid colon.

The inferior mesenteric vein itself is one of the tributaries forming the hepatic portal vein.

By which ligaments are the right and left colic flexures fixed?

The provided sources describe the fixation only of the left colic flexure.

  • Phrenicocolic ligament (lig. phrenicocolicum) — spans between the parietal peritoneum of the diaphragm and the left colic flexure. It serves as a sort of 'hammock' for the inferior pole of the spleen.

Information regarding the suspensory apparatus of the right colic flexure is not provided in the sources.

What is the autonomic innervation of the right and left halves of the colon?

Autonomic innervation of the colon exhibits topographical features described for the parasympathetic division.

  • Parasympathetic innervation: provided by branches of the vagus nerve (n. vagus), which innervate the smooth muscle of the gastrointestinal tract up to the left colic flexure (right half and transverse colon).
  • Sympathetic innervation: derived from the celiac (plexus coeliacus) and superior mesenteric (plexus mesentericus superior) plexuses.

Specific sources of innervation for the left half of the colon (distal to the left flexure) are not detailed in the texts.

What are the transition points between segments of the colon?

At segment transitions: the right colic flexure (flexura coli dextra) is located in the right hypochondrium at the transition of the ascending colon to the transverse colon, and the left colic flexure (flexura coli sinistra) is at the transition of the transverse colon to the descending colon.

Which parts of the colon lie retroperitoneally?

The ascending and descending colons are located retroperitoneally. Their posterior surfaces are apposed to the posterior abdominal wall.

Where is the sigmoid colon located and what is its length?

It lies in the left iliac fossa and the cavity of the lesser pelvis. The average length is 54–55 cm, though significant individual variations occur.

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