The liver performs many important functions. In addition to producing bile, the liver stores glycogen, a complex carbohydrate, and converts it into glucose (sugar) for release
fig. 2.1 Gastrointestinal tract, including where nutrients are absorbed. Iron, fat, sugars, amino acids, and folic acid are absorbed into the duadenum. Vitamins A, D, E, and K, Vitamic C, niacin, and thiamin are absorbed into the jejunum. Vitamin B12 and bile salts are absorbed into the ileum.
into the bloodstream when the blood sugar level falls. Glycogen is deposited in the liver when the blood sugar level is high. This organ also serves as a regulator, determining how much of various kinds of nutrients is sent throughout the body. In addition, the liver metabolizes a number of medications, converting them into the most useful chemical form for treating various illnesses.
The gallbladder is not an essential organ, serving only to store bile produced by the liver that is not being used immediately. It can be removed with minimal consequence.
The pancreas is essential. It produces pancreatic enzymes, which are secreted through the pancreatic ducts into the duodenum and assist in digestion of fats and proteins. The pancreas also produces the hormones insulin and glucagon, which are released directly into the bloodstream and regulate the metabolism of glucose (sugar), amino acids, fatty acids, and glycogen in the liver and other tissues.
When the digestive system is healthy, the transformation of food into energy and waste is automatic. But when the digestive system is damaged by inflammatory bowel disease, any or all of its various components can malfunction, leading to malabsorption, malnutrition, and severe damage to the quality of life.
3. How and Why the Digestive System Malfunctions in People with Crohn Disease or Ulcerative Colitis
The major pathology of the intestinal tract in a person with Crohn disease or ulcerative colitis is chronic inflammation. Inflammation is a natural response when the body's immune system "attacks" a foreign entity (antigen). Inflammation is characterized by four conditions: heat, redness, pain and swelling. The antigen can be viral, bacterial, parasitic, or chemical; it can be a foreign physical object such as a wood splinter or foreign tissue such as a transplanted organ. But with Crohn disease or ulcerative colitis, there is no obvious immediate antigen at hand. The immune response seems inappropriate; the body creates inflammation with no reason to do so.
In cases of Crohn disease or ulcerative colitis, the inflammation occurs in the inside of the gastrointestinal tract. The inflammatory process also causes damage to the cellular structure of the intestine.
The intestine's lining, the mucosa, is thin; inflammation damages it and can break the protective barrier it forms. When ulcerations develop, intestinal tissue is exposed to the harmful effects of intestinal contents, as well as to enzymes released by inflammatory cells.
In ulcerative colitis, the inflammation only affects the mucosa. In Crohn disease, however, the inflammation can go through the mucosa and involve the full thickness of the bowel wall. The nature of tissue involvement helps the gastroenterologist categorize the Crohn disease as either the inflammatory form (in which the inflammation may cause an inflammatory mass), the obstructing form (in which the inflammation on the inside of the intestine actually causes the intestinal opening to close off; scar tissue from healing inflammation can also close it off), or the fistulizing form (where loops of bowel become connected by a fistula that runs from the inside of one loop to the inside of another).
Depending on where in the gastrointestinal tract the inflammation occurs, effects include malabsorption of nutrients, bleeding, diarrhea, fever, and pain.
Inflammation usually has a cause, or precipitator. But researchers have not yet been able to find a specific precipitator for Crohn disease or ulcerative colitis. They can see the primary sign of the malfunction within the gastrointestinal system (the inflammation) and the secondary symptoms (the bleeding, diarrhea, pain, fatigue, and fever). How and why the malfunction occurs is still a mystery.
To date, the best hypothesis can be shown in this equation: genetic factor(s) + environmental precipitator(s) = inappropriate inflammatory response.
Researchers today are focusing on a number of key questions about the inflammatory process. They are trying to determine not only how, but, more important, why the inappropriate inflammatory response occurs in those with Crohn disease and ulcerative colitis. Some of the key questions are: What triggers the immune system response? What is the genetic component? Is there an inflammatory bowel disease gene? What is the effect of environmental factors such as diet, water, and chemicals? What kind of precipitating incidents lead to an initial bout of either Crohn disease or ulcerative colitis? Do other precipitating incidents cause flare-ups?
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