All of the blood that leaves the stomach and intestines must pass through the liver before reaching the rest of the body. The liver is thus strategically placed to process nutrients and drugs that have been absorbed from the digestive tract into forms that are easier for the rest of the body to use. The American Liver Foundation likens the liver to "the body’s refinery." The liver also plays an important role in removing ingested and internally produced toxic substances from the blood. Those substances are converted by the liver into substances that can be easily eliminated from the body. It also makes bile, a fluid which is essential for digestion. Bile is stored in the gallbladder which, after eating, contracts and discharges bile into the intestines, where it facilitates digestion.

The pancreas has two main roles within the human body:

• It produces juices that contain chemicals or enzymes that are collected into the pancreatic duct and are released into the intestine (bowel) through the duct opening. Once in the intestine, the enzymes help to digest food.  The juice break-ups proteins, fats and sugars into smaller pieces, so that the body can use them for energy and growth. This breaking up, or digestion, is performed by chemicals in the juice called enzymes.
• It also produces insulin, a hormone that helps to control the level of glucose sugar in your blood.  The pancreas does this by producing hormones, the most important of which is called Insulin. Insulin causes glucose to leave the bloodstream and enter body tissues. This results in the amount of glucose in the blood falling.

The brain needs glucose as its fuel. Too little glucose in the blood and the brain cannot work correctly. The symptoms of this are like being intoxicated. Occasionally if the amount of glucose in the blood becomes very low, a coma can occur.

Diabetes mellitus is a condition which occurs when the blood glucose remains high over a long period of time. In longstanding diabetes, the kidneys, eyes, blood vessels and nerves can be damaged, so it is important to receive the correct treatment. These effects can be lessened by treatment with diet, drugs or injections of insulin as well as transplantation using tissue engineered islets.