Large Intestine

Frequently asked questions

What parts comprise the colon?

The colon forms a frame surrounding the loops of the small intestine and is divided into four regions:

• Ascending colon (colon ascendens).
• Transverse colon (colon transversum).
• Descending colon (colon descendens).
• Sigmoid colon (colon sigmoideum).

Where do all three taeniae coli anatomically converge?

All three taeniae coli converge on the cecum at the base of the vermiform appendix. At this point, the longitudinal muscle bundles merge into a continuous muscle layer.

This anatomical feature has great clinical significance: the convergence point serves as a reliable landmark for surgeons when locating the base of the appendix during surgery. The taeniae coli represent grouped segments of the outer longitudinal muscular layer, which are absent on the appendix and the rectum.

Which arteries supply blood to the large intestine?

Blood supply to the segments of the large intestine is provided by branches of the superior and inferior mesenteric arteries and their anastomoses:

• Ileocolic artery (a. ileocolica) and its branches — supply the cecum and appendix.
• Right colic artery (a. colica dextra) and anastomoses — supply the ascending colon.
• Middle colic artery (a. colica media) — runs into the transverse mesocolon and divides into right and left branches.
• The right branch of the a. colica media anastomoses with the a. colica dextra and supplies the right half of the transverse colon.
• The left branch of the a. colica media runs to the left half of the transverse colon and anastomoses with the a. colica sinistra — a key anastomosis between the superior and inferior mesenteric arteries forming part of the marginal artery of Drummond.

How do the various segments of the large intestine relate to the peritoneum?

Different segments of the large intestine have varying peritoneal relationships.

Large Intestine Segment	Peritoneal Relationship	Presence of Mesentery
Cecum	Intraperitoneal in 97% of cases	Intraperitoneal without a distinct mesentery; pathological mobility may occur via a common mesentery with the small intestine
Appendix	Intraperitoneal	Has a mesoappendix
Ascending colon	Mesoperitoneal in 70.8% of cases; covered anteriorly and laterally, devoid of peritoneum posteriorly	Has a mesentery along its entire length in 1/3 of cases
Transverse colon	Intraperitoneal	Has a well-developed mesentery — mesocolon transversum
Descending colon	Mesoperitoneal in 55% of cases	May present with a pronounced mesentery or a mesentery along a short segment
Sigmoid colon	Intraperitoneal	Has a well-developed mesentery

What are the main functions of the large intestine?

The large intestine performs four key functional tasks ensuring completion of digestive processes and fecal formation. These include:

• Absorption — intensive reabsorption of water from chyme.
• Fecal formation — binding indigestible food residues through active mucus production, facilitating their passage through the gut.
• Excretory function — elimination of heavy metal salts, phosphates, calcium, and magnesium ions from the blood into the lumen.
• Bacterial activity — resident microflora synthesize vitamins (K and B12 group) and partially break down cellulose.

Additionally, external self-regulation mechanisms control rectal emptying (defecation).

How can you distinguish the large intestine from the small intestine on a histological or gross specimen?

The large intestine has a larger diameter, prominent longitudinal muscular bands (taeniae coli), sacculated haustra, and fatty omental appendices.

Are there villi in the large intestine?

No, the mucosa of the large intestine completely lacks intestinal villi, but it contains numerous deep crypts.

Where does the large intestine begin and end?

It begins at the ileocecal junction and ends at the anal opening of the rectum.