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Digestive health centre

Colon conditions, tests and treatments

The colon is part of digestive system, also known as the large intestine.

The colon performs tasks in the human waste disposal system, removing water, salt and some nutrients, forming poo or stool.

Muscles line the colon's walls, squeezing the contents along.

Billions of helpful bacteria coat the inner walls of the colon and its contents, helping to maintain a healthy balance in the body.

Picture of the colon

The ileum (last part of the small intestine) connects to the caecum (first part of the colon) in the lower right abdomen. The rest of the colon is divided into four parts:

  • The ascending colon travels up the right side of the abdomen.
  • The transverse colon runs across the abdomen.
  • The descending colon travels down the left abdomen.
  • The sigmoid colon is a short curving of the colon, just before the rectum.


Colon conditions

  • Colitis: Inflammation of the colon. Inflammatory bowel disease or infections are the most common causes.
  • Diverticulosis: Small weak areas in the colon's muscular wall allow the colon's lining to protrude through, forming tiny pouches called diverticuli. Diverticuli usually cause no problems, but can bleed or become inflamed.
  • Diverticulitis: When diverticuli become inflamed or infected, diverticulitis results. Abdominal pain and constipation are common symptoms.
  • Colon bleeding (haemorrhage): Multiple potential colon problems can cause bleeding. Rapid bleeding is usually visible in the stool, but very slow bleeding might not be.
  • Inflammatory bowel disease: A name for either Crohn's disease or ulcerative colitis. Both conditions can cause colon inflammation (colitis).
  • Crohn's disease: An inflammatory condition that usually affects the colon and intestines. Abdominal pain and diarrhoea (which may be bloody) are symptoms.
  • Ulcerative colitis: An inflammatory condition that usually affects the colon and rectum. Like Crohn's disease, pain and bloody diarrhoea are common symptoms of ulcerative colitis.
  • Diarrhoea: Stools that are frequent, loose, or watery are commonly called diarrhoea. Most diarrhoea is due to self-limiting, mild infections of the colon or small intestine.
  • Salmonellosis: The bacteria salmonella can contaminate food and infect the intestine. Salmonella causes diarrhoea and stomach cramps, which usually resolve without treatment.
  • Shigellosis: The bacteria shigella can contaminate food and invade the colon. Symptoms include fever, stomach cramps and diarrhoea, which may be bloody.
  • Travellers' diarrhoea: Many different bacteria commonly contaminate water or food in developing countries. Loose stools, sometimes with nausea and fever, are symptoms.
  • Colon polyps: Polyps are small growths. Some of these develop into cancer, but it takes a long time. Removing them can prevent many colon cancers.
  • Bowel cancer: Cancer of the bowel (also called colorectal cancer) is diagnosed in more than 40,000 people each year in the UK.

Colon tests

  • Colonoscopy : An endoscope (flexible tube with a camera on its tip) is inserted into the rectum and advanced through the colon. A doctor can examine the entire colon with a colonoscope.
  • Virtual colonoscopy: A test in which an X-ray machine and a computer create images of the inside of the colon. If problems are found, a traditional colonoscopy is usually needed.
  • Stool occult blood testing: A test for blood in the stool. If blood is found in the stool, a colonoscopy may be needed to look for the source.
  • Sigmoidoscopy: An endoscope is inserted into the rectum and advanced through the left side of the colon. Sigmoidoscopy cannot be used to view the middle and right sides of the colon.
  • Colon biopsy: During a colonoscopy, a small piece of colon tissue may be removed for testing. A colon biopsy can help diagnose cancer, infection or inflammation.

WebMD Medical Reference

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