The colon is the medical name for the large bowel. It is the part of the gut or gastrointestinal tract that makes the stool or faeces by absorbing water.

When we eat and drink, the food and drink get swallowed down the oesophagus or gullet into the stomach. Here the digestion process starts with the stomach acid. Bit by bit, the food is made into a liquid to make a nutrient easy to absorb, and then it gets squirted from the stomach into the small intestine.

The liquid food passes down the small intestine (duodenum, jejunum then ileum) the length of all of the small bowel being approximately 180 cm (6 feet). The small intestine absorbs all of the nutrients out of the food mixture, leaving just water, fibre and any other waste products. If this was then discharged from the body, it would be a large volume of fluid and we would become very dehydrated and lose many of our salts. Therefore it is the job of the colon to process this waste, removing the useful water and salts and leaving behind just some solid waste - the stool or faeces.

The colon is split into four parts - the ascending colon, transverse colon, desending colon and sigmoid colon. The small bowel enters the a ascending colon in the right lower abdomen, at the junction called the ileocaecal valve. The first part of the ascending colon is dilated like a sac of bowel and is called the caecum. The appendix comes off the bottom of the caecum.

The ascending colon goes from the right lower abdomen to the right upper abdomen, where it sits just under the liver. It is then turns and runs across the abdomen, where it is called the transverse colon. When it gets to the left ribs by the spleen, it then turns downwards and is called the descending colon. This then runs down the left side of the abdomen until it gets near the pelvis. Here it moves into a 25 cm long segment or mobile colon which is S-shaped and therefore is called the sigmoid colon. The sigmoid colon then empties into the rectum at the pelvis - at a junction called the rectosigmoid junction.

At the start of the colon, the contents are very fluid. By the end of the colon, the contents are very solid and harder to move. This is why when one gets constipated, the pain is often on the left-hand side - at the point of the sigmoid colon.

The colon is an essential structure. There are several diseases that can be associated with it including colonic cancer or inflammation called colitis, ulcerative colitis or Crohn's disease. If the colon is ever removed, the patient has to cope with the waste products which are very fluid and high-volume.

Specialists who specialise in colonic conditions and diseases are either physicians called gastroenterologists or surgeons called colorectal surgeons.