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Crohn's disease


How does the digestive system work?

Your digestive system, or GI tract, is made up of several organs that together help your body take in food, break it down, distribute nutrients and get rid of waste. 

The upper GI tract includes the mouth, pharynx, oesophagus and stomach. Food is taken in through the mouth, chewed and swallowed down past the pharynx, then passed down through the oesophagus and into the stomach.

The lower GI tract includes the large intestine, small intestine and anus. The small intestine has three parts: the duodenum (the first and shortest part of the small intestine, where most chemical digestion takes place), the jejunum (the middle part of the small intestine, largely responsible for absorption of nutrients), and the ileum (mainly responsible for absorbing vitamin B12, bile salts and other nutrients).

The large intestine includes the caecum (a pouch that connects the ileum to the large intestine, which aids in the breakdown of materials such as cellulose), colon (which removes water and salt and stores wastes) and rectum (the final part of the large intestine which serves as a storage area for waste). 

The anus is the outer opening of the rectum and is mainly responsible for storing and getting rid of waste from the body. 

Crohn's disease can affect any area of the GI tract, from the mouth to the anus. It affects only the small intestine in about 1/3 of people, both the small intestine and large intestine in about 1/3 of people, and only the large bowel in 1/3 of people. The inflammation (swelling) extends deep into the lining of the affected area, which can cause pain and can make the intestines empty often, leading to diarrhoea and an urge to go to the toilet often. There may be normal healthy bowel in between patches of diseased bowel.  

Ulcerative colitis, in comparison, only affects the colon (large intestine) and also only affects the mucosa (lining) of the colon. 

Here is a list of the different types of Crohn's disease and how they might affect you.


  • Ileocolitis: This is the most common form of Crohn's disease. It affects both the ileum and colon. Symptoms include diarrhoea and cramping or pain in the right lower part or middle of the abdomen. It often causes weight loss.


  • Ileitis: This only affects the ileum. Symptoms include diarrhoea, cramping or pain in the lower right or middle part of the abdomen.

In SEVERE cases

In severe Crohn's disease, complications of ileitis may include fistulas (tunnels caused by inflammation) or inflammatory abscess (pockets of infection) in the right lower area of the abdomen.


  • Gastroduodenal Crohn's disease: This affects the stomach and duodenum (the first part of the small intestine). Symptoms may include weight loss, loss of appetite and nausea.

In SEVERE cases

In severe gastroduodenal Crohn's disease, vomiting may indicate a blockage in the intestine (an obstruction).

  • Jejunoileitis: This causes patchy areas of inflammation in the jejunum (upper half of the small intestine). Symptoms may include abdominal pain, ranging from mild to intense, and cramps following meals, as well as diarrhoea.

In SEVERE cases

In severe jejunoileitis, complications may include fistulas.


  • Crohn's colitis: Affects the colon only. Symptoms may include diarrhoea, rectal bleeding, infections and disease around the anus, or ulcers on the skin. Skin lesions and joint pains are more common with this form than with other forms of Crohn's disease.

In SEVERE cases

In severe Crohn's colitis, symptoms may also include fistulas (tunnels caused by inflammation between different parts of the bowel, or between the bowel and the skin) or inflammatory abscesses (pockets of infection).



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