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.

comparing crohn's disease and ulcerative colitis

There are several differences between Crohn's disease and ulcerative colitis. These characteristics are summarized in the table below. 
  Crohn's Disease Ulcerative Colitis

More females than males
All ages, peak onset 15-35 years

Similar for females and males
All ages, usual onset 15-45 years
Symptoms Diarrhea, fever, sores in the mouth and around the anus, abdominal pain and cramps, anemia, fatigue, loss of appetite, wight loss Bloody diarrhea, mild fever, abdominal pain and cramps, anemia, fatigue, loss of appetite, weight loss
Terminal Ileum involvement Common Never
Colon Involvement Common Always
Rectum involvement Common Always
Peri-anal disease Common Never
Distribution of disease Patchy areas of inflammation Continuous areas of inflammation but can be patchy once treated
Endoscopic findings Deep and snake-like ulcers Diffuse ulceration
Depth of inflammaton May be transmural, extending through the entire thickness of the wall of an organ or cavity deep into tissues Shallow, mucosal
Fistulas between organs Common Never
Stenosis Common Never
Granulomas on biopsy Common Never
Effect of surgery Often return following removal of affected parts. Decreased likelihood of pregnancy Usually cured by removal of colon (colectomy). Decreased likelihood of pregnancy after ileoanal pouch
Treatment options Drug treatment (corticosteroids, immune modifiers, biologic therapies). Exclusive formula diet in children. Surgery (repair fistulas, remove obstruction, resection, and anastomosis). Drug treatment (5-aminosalicylates, sulfasalazine, corticosteroids, immune modifiers, biologic therapies). Surgery (rectum/colon removal) with creation of an internal pouch (ileoanal pouch).
Cure No existing cures. Maintenance therapy is used to reduce the chance of relapse. Through colectomy only. Maintenance therapy is used to reduce the chance of relapse.
Bowel complications Blockage of intestine due to swelling or formation of scar tissue. Abscesses, sores or fistulas. Malnutrition. Colon cancer Bleeding from ulcerations. Perforation (rupture) of the bowel. Malnutrition. Colon Cancer
Extra-intestinal disease Osteoporosis. Liver inflammation (primary sclerosing cholangitis). Blood Clots. Pain and swelling in the joints (arthritis). Growth failure (in children). Mental Illness. Liver inflammation (primary sclerosing cholangitis). Blood clots. Eye inflammation (iritis). Pain and Swelling in the joints (arthritis). Mental illness.
Smoking Higher risk of acquiring for smokers Higher risk of acquiring for ex-smokers
Mortality risk Increased risk of colorectal cancer and overall mortality. Increased risk of lymphoma and skin cancer (due to treatments). Increased risk of colorectal cancer. Uncertain change in mortality risk. Increased risk of lymphoma and skin cancer (due to treatments).

Image reference. Impact of Inflammatory Bowel Disease in Canada. 2018.

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, visit our Newly Diagnosed page for more information and resources. 

strengthen your knowledge of living with crohn's and colitis

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

find a community near you

Your local chapter of Crohn’s and Colitis Canada is a powerhouse of health information and support. Through education, presentation and discussion, people can find resources to help them cope with their Crohn’s, and meet others who are living with Crohn’s or colitis.

Visit our Find My Community page to look up the chapter closest to you. It’s in your best interest to get active and informed!

  • 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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