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How the Liver Works

The liver is an amazing organ. It is one of the largest organs in the body and receives 25% of the blood that the heart pumps with each beat. The liver performs many, many functions that are necessary to keep a person alive. Some of these functions are summarized below.

The liver makes necessary proteins for the body. This function is called the liver's "synthetic function." Many patients with liver disease have normal synthetic function until disease is very bad. The liver makes coagulation factors, proteins that help the blood to clot. This protects us from bleeding. When the liver is failing, it cannot make clotting factors. A blood test that measures blood clotting is called PT/PTT or pro-time (sometimes also referred to as INR). When the liver cannot make clotting factors, the pro-time is abnormally high. Another protein that the liver makes is called albumin. This small protein helps to keep fluid in the bloodstream and prevents swelling or accumulation of fluid outside the blood vessels of the body. When the liver does not work well, the albumin is low. Other conditions, such as malnutrition or loss of albumin in the stool or urine, can also make the albumin be low.

The liver also makes bile, which helps us absorb food and eliminate toxins. Bile salts, which come from the liver and are dumped into the intestine via the bile duct, help us absorb fats in our diet. When the liver is not functioning well, bile may not be made or pumped out adequately. Patients may develop diarrhea and malnutrition. One of the substances that bile carries out of the body is called bilirubin. Bilirubin comes from broken-down red blood cells, which all of us recycle about once in 90 days. Bilirubin normally exits the body through bile and gives stool its brown color. Patients with poor liver function or with blockage to bile flow cannot get rid of bilirubin, which builds up in the bloodstream. This may cause the patient to be jaundiced or yellow in color. Cholesterol also leaves the body through bile and patients with poor bile flow may develop cholesterol deposits in their skin. These bumps are called xanthomata.

One of the liver's most important functions is to "detoxify" the blood. The liver receives blood from the intestine. This blood is full of nutrients but also contains toxins and other chemicals that the liver cleans up before they enter the body's circulation. In patients with very poor liver function, the liver may not be able to clean up the blood. Ammonia, which is a byproduct of protein metabolism, may accumulate. Other chemicals that we are not able to identify build up as well. This may make patients with very poor liver function have confusion or changes in their mental state. In very severe disease, liver failure can even cause coma and brain swelling.

The liver also helps the body fight infection. The liver contains a number of macrophages (immune cells) called Kupffer cells. For a variety of reasons, patients with severe liver disease do not fight infection well. They are more prone to infections of the bloodstream and other tissues.

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