The digestive tract is a single tube that exists between the mouth and the anus, with many folds and convolutions. There are four main parts in this tube (such as the esophagus, stomach, small intestine, and large intestine), each with its own specific structure and function. Solid organs such as the liver and pancreas are also considered portions of the digestive system.
The hollow parts of the digestive tract are responsible for breaking down large portions of food into small molecules that can be readily absorbed into the circulation. The sterile bloodstream is separated from the mass of nutrients, toxins, and organisms in various parts of the hollow digestive tract by only a very thin layer of cells, collectively called the intestinal mucosa. This delicate and complex lining is responsible for secreting substances that aid in digestion and absorption of nutrients, and for defending the body against the toxins and other contaminants in the intestine itself (Abraham 2009).
During healthy conditions, the immune cells in the intestinal lining cope with invaders quickly and efficiently, without producing excessive amounts of localized inflammation. However, in inflammatory bowel disease, inflammation becomes uncontrolled. Cytokines released by inflammatory cells in the intestine attract additional immune cells that produce destructive chemicals and propagate inflammation (Neuman 2004). Since the inflammatory reactions taking place in the gut can promote systemic inflammation people with IBD should monitor levels of inflammatory cytokines in their blood. Cytokine testing can be used as a measure of the effectiveness of anti-inflammatory therapies, and can also help determine risk for other conditions associated with inflammation, such as atherosclerosis.