General topography
The colon (colon) is located in the abdominal cavity and lesser pelvis. Its main topographical feature is the formation of a frame around the loops of the small intestine.
Depending on the direction of its course and location, four parts are distinguished:
- ascending colon (colon ascendens);
- transverse colon (colon transversum);
- descending colon (colon descendens);
- the sigmoid colon (colon sigmoideum).
Right half of the colon
The ascending colon originates from the cecum. It is located in the right part of the abdominal cavity, ascending up to the level of the right hypochondrium. Its posterior surface lies against the posterior abdominal wall, as it is situated retroperitoneally. In the region of the right hypochondrium, the colon bends to form the right colic flexure (flexura coli dextra) and continues into the next section.
The transverse colon begins at the right flexure and runs to the left, ending at the left colic flexure (flexura coli sinistra). It lies in the upper floor of the abdominal cavity, and its projection usually corresponds to the level of the cartilage of the 10th rib. Unlike the ascending part, it is covered by the peritoneum on all sides (intraperitoneally) and has its own mesentery—mesocolon transversum. The presence of the mesentery provides this segment with significant anatomical mobility.
Left half and transition to the lesser pelvis
The descending colon begins at 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 cavity of the lesser pelvis. Its length averages 54–55 cm, although this parameter can vary greatly among individuals. The sigmoid colon, like the transverse colon, is completely covered by the peritoneum and has a mesentery (mesocolon sigmoideum), which determines its high degree of mobility. The colon ends by transitioning into the rectum; this transition is projected at the level of the 3rd sacral vertebra.
Briefly: answers to topical questions
Where is the left colic flexure (flexura coli sinistra) topographically located?
The left colic flexure (flexura coli sinistra) is located in the left hypochondrium at the level of the 9th rib cartilage or the eighth intercostal space. Topographically, it lies approximately 4 cm higher and deeper (dorsally) than the right colic flexure. Superiorly, the flexure approaches the lower pole of the spleen, and posteriorly it adjoins the left kidney, from which it is separated by the 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 tenia coli.
- Omental appendices (appendices epiploicae / omentales) — projections of the serous membrane containing adipose tissue.
Which arteries supply blood to 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 to the middle section of the ascending colon; its ascending branch goes to the right colic flexure and anastomoses with the middle colic artery.
- Middle colic artery (a. colica media) enters the mesentery of the transverse colon and divides into right and left branches. The right branch anastomoses with a. colica dextra and is connected to the right flexure and the right half of the transverse colon; the left branch goes to the left half of the transverse colon and anastomoses with a. colica sinistra.
Which vein receives venous drainage from the descending and sigmoid colon?
Venous drainage from the descending and sigmoid colon flows into the inferior mesenteric vein (v. mesenterica inferior).
The following tributaries drain into this venous collector:
- 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 roots of the hepatic portal vein.
What ligaments fix the right and left colic flexures?
The provided sources describe the fixation of only the left colic flexure.
- Phrenicocolic ligament (lig. phrenicocolicum) — stretched between the parietal peritoneum of the diaphragm and the left colic flexure. It serves as a kind of "hammock" for the lower pole of the spleen.
Information about the ligamentous apparatus of the right colic flexure is absent in the sources.
What is the autonomic innervation of the right and left halves of the colon?
The autonomic innervation of the colon has topographic features described for the parasympathetic division.
- Parasympathetic innervation: is provided by branches of the vagus nerve (n. vagus), which innervate the smooth muscles of the gastrointestinal tract down to the left colic flexure (the right half and the transverse colon).
- Sympathetic innervation: is derived from the celiac (plexus coeliacus) and superior mesenteric (plexus mesentericus superior) plexuses.
Specific sources of innervation for the left half of the colon (below the left flexure) are not detailed in the texts.
To remember the mobility of the parts: the "vertical" segments (ascending and descending) are retroperitoneally fixed and immobile, whereas the "horizontal/tortuous" segments (transverse and sigmoid) possess a mesentery and are freely movable.
Class and exam questions
At junction sites: the right colic flexure (flexura coli dextra) marks the transition of the ascending colon into the transverse colon, and the left colic flexure (flexura coli sinistra) marks the transition of the transverse colon into the descending colon.
At junction sites: the right colic flexure (flexura coli dextra) is located in the right hypochondrium where the ascending colon transitions into the transverse colon, and the left colic flexure (flexura coli sinistra) marks the transition of the transverse into the descending colon.
Which parts of the colon are retroperitoneal?
The ascending and descending colons are situated retroperitoneally. Their posterior surfaces lie against the posterior abdominal wall.
Where is the sigmoid colon located and what is its length?
It lies in the left iliac fossa and the pelvic cavity. The average length is 54–55 cm, though significant individual variations are possible.
What else to study on this topic
- Structure of the colonic wall
- Sphincters of the large intestine
- Blood supply to the colon
- Venous and lymphatic drainage
- Innervation of large intestine segments
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