What are Crohn’s and Colitis?

Crohn's disease and ulcerative colitis are diseases that inflame the lining of the GI (gastrointestinal) tract and disrupt your body's ability to digest food, absorb nutrition, and eliminate waste in a healthy manner.

As a result, you might have any of the following symptoms: abdominal pain, cramping, gas, bloating, fatigue, diarrhea (possibly bloody) and loss of appetite.

Inflammatory bowel disease (IBD) describes a group of conditions, the two main forms of which are Crohn's disease and ulcerative colitis. IBD also includes indeterminate colitis.

Dr. Mike Evans is founder of the Health Design Lab at the Li Ka Shing Knowledge Institute, an Associate Professor of Family Medicine and Public Health at the University of Toronto, and a staff physician at St. Michael's Hospital. This video was made possible through the Gastrointestinal Society, with the support of Crohn's and Colitis Canada

Crohn's Disease:

With Crohn's disease, inflammation can occur anywhere in the GI tract but is usually present in the lower part of the small bowel and the colon. Patches of inflammation occur between healthy portions of the gut, and can penetrate the intestinal layers from inner to outer lining. Learn more about Crohn's disease.

Ulcerative Colitis:

Ulcerative colitis only affects portions of the large intestine, including the rectum and anus and typically only inflames the innermost lining of bowel tissue. It almost always starts at the rectum, extending upwards in a continuous manner through the colon. Ulcerative colitis can be controlled with medication and, in severe cases, surgically removing the entire large intestine may be considered as a treatment. Learn more about ulcerative colitis.

Indeterminate Colitis:

Indeterminate colitis is a term used when it is unclear if the inflammation is due to Crohn's disease or ulcerative colitis.

Anatomy and Function of the GI Tract

In order to understand Crohn's disease and ulcerative colitis, it is first helpful to understand the anatomy and function of the healthy gastrointestinal (GI) tract.

Here is a medical illustration of the GI tract:

A medical illustration of the GI tract

As you can see, when you eat, food travels through the GI tract in the following order: 

Mouth [ 1 ]

Esophagus [ 2 ] (the tube that connects the mouth to the stomach)

Stomach [ 3 ] (where food is mixed with stomach acid and enzymes to break down the material into smaller pieces called chyme)
Small Bowel [ 4 ] (also known as the Small Intestine) which is made up of three sections known as the: 
  • Duodenum [ 7 ] (about 8 cm in length)
  • Jejunum [ 8 ] (can be around 3 metres long)
  • Ileum [ 9 ] (can also be approximately 3 metres in length)

The functions of the small bowel are to digest your food and absorb the nutrients that are necessary for life. Many people believe that this is the purpose of the stomach but that is not true. The small bowel (particularly the jejunum and ileum) is the organ responsible for absorbing nutrients from your food. Without the small bowel, we would not be able to convert food into useable nutrition.

Ileocecal Valve [ 5 ] (which regulates the amount of material passed from the small bowel to the large bowel and prevents "dumping" all at once

Large Bowel [ 6 ] (also called the Large Intestine or the Colon). The colon is much wider in diameter than the small bowel and is approximately 1.5 metres long. Once again, there are sections of the colon which are identified by different names to enable discussion about clinical issues :
  • Cecum [ 10 ] and appendix [ 11 ] 
  • Ascending colon 
  • Hepatic flexure (a bend in the gut at close to the location of the liver) 
  • Transverse colon 
  • Splenic flexure (another bend located near the spleen) 
  • Descending colon 
  • Sigmoid colon 
  • Rectum [ 12 ]
  • Anus [ 13 ]

The main functions of the colon are to extract water and salt from stool, and store it until it can be expelled via the anus. When stool first enters the colon from the small bowel, it is very watery. As it traverses the large bowel, water is reabsorbed and the stool gradually becomes firmer.

The Scoop on Poop

Let's talk a bit about stool, also known as feces. It may seem glib and a bit crass to kid around about toilet humour and "the scoop on poop". However, the fact of the matter is that bowel function is a normal, absolutely necessary function of the human body.

When it is not normal - as with Crohn's or colitis - all kinds of trouble can result. We, like many who deal with these diseases, address the issues of bowel function and feces in a direct manner, and occasionally with humour, with the best of intent and the desire to help you face this disease openly and frankly. Our aim is to take Crohn's and colitis out of the shadows, where it will remain unless more people talk about it directly.

Stool is the by-product of digestion through the GI tract. In a healthy individual, it is usually composed of water, dead and living bacteria, fiber (undigested food), intestinal mucous and sloughed-off lining of the gut. It is not normal to have blood in feces, nor large amounts of mucous. Stool from an individual without any gut disease is soft enough to pass comfortably from the rectum and anus, and (depending on the person) is typically expelled one or two times a day.

Bowel movements are an entirely different matter for someone with Crohn's or colitis. Individuals with these diseases face some very real challenges related to feelings of urgency, diarrhea and bloody stool. Visit our Signs and Symptoms page to learn more. 

Have you been recently DIAGNOSED with Crohn's or colitis?

If you have been recently diagnosed with Crohn's or colitis, check out our Newly Diagnosed page for more information and resources. 

learn more about living with crohn's and colitis

Visit our Living with Crohn's and Colitis page to learn about diet and nutrition in IBD, treatment options, symptom management and other essential information.  

  • Canada has among the highest incidence rates of Crohn's and colitis in the world.
  • 1 in 140 Canadians lives with Crohn’s or colitis.
  • Families new to Canada are developing these diseases for the first time.
  • Incidence of Crohn’s in Canadian kids under 10 has doubled since 1995.
  • People are most commonly diagnosed before age 30.

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