The liver's main function is to filter the blood. It helps guard you from infection and removes bacteria and other toxic substances from your blood to help you stay healthy.

The liver performs many important functions:

• Cleans and purifies the blood supply, breaks down certain chemical substances in the blood, and manufactures (synthesizes) others
• Stores energy that drives your muscles
• Helps regulate your blood sugar and control your cholesterol and several hormones and enzymes

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Purification
The liver changes toxic substances like alcohol and nicotine into harmless substances.

Although this is good for the body as a whole, liver cells can be damaged in the process. Detoxification of alcohol, for example, can harm the liver, leading to cirrhosis.

The liver also changes certain medicines into a form your body can use, and inactivates other medicines after they've worked.

Synthesis
The liver takes simple chemical building blocks and combines them to manufacture (synthesize) more complex substances. For example, the liver manufactures most of the proteins found in the blood, as well as those needed to clot blood, make new cells, and cause chemical reactions inside of cells.

Storage
The liver changes blood sugar (glucose) into a storage form (glycogen). When the body needs energy, the liver releases the sugar into the bloodstream. The liver also stores vitamins and minerals until they are needed in other areas of the body.

Transformation
The liver uses enzymes to transform small building blocks (amino acids, sugars, and fatty acids) into other building blocks. An excess of one of these enzymes, alanine aminotransferase (ALT), is found in the blood when liver cells have been damaged.

The liver, which inactivates certain hormones, regulates the amount of testosterone and estrogen in the blood. It also plays a major role in breaking down and building up cholesterol.

When the Liver is Injured
The normal liver is smooth and firm to the touch. When the liver is diseased (for example, with hepatitis C), it becomes inflamed (swollen). The liver cells begin to leak out an enzyme known as alanine aminotransferase (ALT) into the blood. This is one way doctors can tell whether you have liver damage. If ALT levels in the blood are higher than normal, it is usually a sign of liver damage. As liver disease progresses, changes occur and damage to the liver increases.

Fibrosis. After becoming inflamed, the liver tries to repair itself by forming tiny scars. This scarring, called "fibrosis," makes it difficult for the liver to do its job. As damage continues, many scars form and begin to join together, leading to the next stage, cirrhosis.

Cirrhosis. With repeated damage, large areas of the liver can become permanently scarred and nodules (bumps) may form. Blood cannot flow freely through scarred liver tissue. The liver begins to shrink and becomes hard. Chronic hepatitis C is a common cause of cirrhosis of the liver, as is excessive drinking.

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Liver failure. As cirrhosis worsens, the liver becomes unable to filter wastes, toxins, and drugs from the blood. It can no longer produce the clotting factors necessary to stop bleeding. Fluid builds up in the abdomen and legs, bleeding in the intestines is common, and eventually mental functioning is slowed. At this point, a liver transplant is the only option.

Liver cancer. Sometimes damage to liver cells includes altering the genes inside cells in a way that causes them to become cancerous. Patients with chronic hepatitis C are at higher risk for hepatocellular carcinoma, a type of liver tumor.

A recent study published in the New England Journal of Medicine attributed an increase in the number of cases of hepatocellular carcinoma in the United States over the past 20 years to the spread of hepatitis B and hepatitis C viruses.

Preventing Liver Damage
Cirrhosis can be stopped and sometimes even prevented. For patients with chronic hepatitis C, it is important to prevent greater damage to the liver that would make cirrhosis even worse. Therefore, if you have hepatitis C, avoid alcohol completely. Also, do not combine alcohol and acetaminophen (an ingredient in some over-the-counter pain relievers and in many drug combinations used for colds), because when taken together they can cause a condition called fulminant hepatitis, which can lead to fatal liver failure. Clearly, you should closely follow your doctor's instructions about present and future medications and diet.

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