Colon

The colon is part of the digestive system.

Function of the colon

The colon is also called the large bowel and follows the small bowel forming the last part of the digestive system. It has several parts:

• the caecum (from which the appendix begins);
• the ascending colon (right colon);
• the transverse colon;
• the descending colon (left colon);
• the sigmoid colon;
• and the rectum.

Its main role is to remove waste, absorb water, maintain water balance and absorb certain vitamins. The chyle which comes from the small intestine has already had almost all (90%) of its nutrients absorbed by the digestive system. Chyle mixes with mucus and intestinal bacteria in the colon to form faecal matter. Bacteria which can digest fibres form new molecules that the colon can then absorb.

Its pH is between 4.5 and 7.5.

Structure of the colon

The colon is 1 to 1.5 meters long and 4 to 8 centimetres in diameter (the rectum and caecum respectively). It is composed of several layers, from the inside to the outside consisting of:

• a mucosa which contains no valves or valvules;
• a highly vascularised innervated sub-mucosa;
• circular (internal) and longitudinal (external);
• smooth muscles and a serous lining (peritoneum).