Crohn's disease is a chronic (ongoing) disorder that causes inflammation of the digestive or gastrointestinal (GI)
tract, most commonly affecting the small intestine and/or colon.
This disease marked by an abnormal response by the body's immune system. The immune system is composed of various cells and proteins. Normally, these protect the body from infection. In people with Crohn's disease, however, the immune system reacts inappropriately.
Although Crohn's disease most commonly affects the end of the small intestine (the ileum) and the beginning of the large intestine (the colon), it may involve any part of the GI tract. All layers of the intestine may be involved, and there can be normal healthy bowel in between patches of diseased bowel.
Although considerable progress has been made in Crohn’s research, investigators do not yet know what causes this disease. Studies indicate that the inflammation in Crohn’s involves a complex interaction of factors: the genes the person has inherited, the immune system, and something in the environment. Foreign substances (antigens) in the environment may be the direct cause of the inflammation, or they may stimulate the body's defenses to produce an inflammation that continues without control. Researchers believe that once the patient's immune system is "turned on," it does not know how to properly "turn off" at the right time. As a result, inflammation damages the intestine and causes the symptoms. That is why the main goal of medical therapy is to help patients regulate their immune system better.
Symptoms may range from mild to severe. Because Crohn's is a chronic disease, patients will go through periods in which the disease flares up, is active, and causes symptoms. These episodes are followed by times of remission -- periods in which symptoms disappear or decrease and good health returns. In general, though, people with Crohn's disease lead full, active, and productive lives.
Source: www.ccfa.org