What Is the Colon?

The colon is the part of the large intestine, lying between the cecum and the rectum (Picture 1). It is the muscular tube, which starts in the lower right abdomen as the continuation of the small intestine, runs up as the ascending colon toward the liver, turns left and runs below the rib cage as the transverse (horizontal) colon toward the spleen, and turns down as the descending colon toward the pelvis, where it widens into the sigmoid colon that continues to the rectum. Its main function is to form a semi-solid stool from the undigested watery food remnants, and push it toward the sigma, where it is stored before being expelled out from the body.

Anatomy of abdomen, digestive system

Picture 1. Colon - the part of the large intestine lying between the cecum and the rectum
(source: Wikimedia)

What Is Colitis and What Causes It?

Colitis refers to inflammation of the inner (mucosal) layer of the colon as a response to microbes or other harmful stimuli. During a colonoscopy, a swollen mucosa or ulcers can be seen and inflammatory cells can be seen in a sample of mucosa under the microscope.

Colitis may be caused by:

Inflammation of the rectum is called proctitis.

Symptoms of Colitis

Sometimes, an affected person is not even aware of having colitis. However, in most cases, one or more of the following symptoms are present in all types of colitis:

Symptoms may appear suddenly or develop slowly during months, depending on the cause.

Signs of Colitis

Signs of colitis (as detected by a doctor during physical examination) are not characteristic and include:

  • Tenderness upon pressing on the abdominal wall
  • Stomach distension
  • Occasionally: raised body temperature, skin rash, mouth ulcers, cracks (fissures) around the anus, small openings in the groin or in the stomach wall through which a fluid or liquid stool may pour out

Types of Colitis

Known types of colitis include:

The term indeterminate colitis is used, when inflammation is found in the colon but the cause or the type of the colitis can not be determined.

The term spastic colitis or spastic colon is used when no inflammation or other organic change can be found in the colon but the colon is irritated (and hence spasms) by food or stress. Nowadays, a term irritable bowel syndrome (IBS) is used for this condition.

Diagnosis of Colitis

The type of colitis may be sometimes hard to determine and often a combination of positive results from several tests are required to make a diagnosis:

  • Personal history
    • Short term (hours to weeks) symptoms like left or right side stomach pain, diarrhea, blood in the stool, and fever are suspicious for infectious colitis due to
      • food poisoning
      • antibiotic therapy (pseudomembranous colitis caused by Clostridium difficile)
    • Long term (months to years) symptoms
      • in an adolescent or adult: Crohns’ disease, ulcerative colitis
      • after 50: ischemic colitis
  • Blood tests: Leukocytes may be elevated in infectious colitis and inflammatory bowel disease (Crohn’s disease, ulcerative colitis)
  • Stool tests: Hemoccult may reveal blood in the stool in any type of colitis. Negative test does not exclude colitis!
  • X-ray with barium enema may show big ulcers, like in ulcerative colitis, or narrowings (in Crohn’s disease)
  • CT may show thickened colonic wall and eventual abscesses in and around the colonic wall
  • Colonoscopy may show swollen mucosa with ulcers but sometimes no changes can be seen
  • Biopsy means cutting off a small piece of colonic mucosa  for histologic investigation (checking the tissue under the microscope). Often only at this stage a diagnosis of colitis and its exact type can be made. 
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Article reviewed by Dr. Greg. Last updated on April 12, 2011