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Definition

The liver is the largest gland and largest internal organ in the human body (the skin is the largest organ overall).

Description

Weighing 3-3.5 lbs (1.4-1.6 kg), the liver is a dark red, wedge-shaped gland approximately eight and a half inches long (roughly the size of a football). It is located in the right side of the abdominal area just below the diaphragm and above the stomach.

Approximately 1.5 qts (1.5 L) of blood flow through the liver each minute. The liver holds about 13% of the body's blood supply. It is furnished with blood from two large vessels, the portal vein and the hepatic artery (hepatic means liver). Blood that has circulated through the stomach, spleen, and intestine enters the liver through the portal vein as part of the portal circulation system. The liver extracts nutrients and toxins from this blood, which is then returned through the hepatic vein to the right side of the heart. The hepatic artery supplies oxygenated blood directly from the heart to the liver.

Function

Some of the liver's many important functions include:

• Production of bile which is stored in the gall bladder and used to digest fats. If the excretion of bile is blocked, the stools become pale and retain fat. As a result, fat-soluble vitamins (vitamins A, D, E, and K) are not properly absorbed and levels of bilirubin, the main component of bile, rises in the blood. Once bilirubin levels reach a certain level, jaundice or yellowing of the skin and eyes occurs.
• Synthesis of proteins, including albumin. Albumin is the predominant protein in blood plasma and helps to retain fluid within the blood vessels. The loss of albumin results in fluid shifting from blood vessels to the surrounding tissue. The result is swelling of tissue, a condition called edema.
• Production of blood-clotting factors that control bleeding. Loss of clotting factors leads to increased chance of hemorrhage.
• Metabolism of hormones and medications, such as estrogen and acetominophen (Tylenol). When the liver is damaged, its ability to metabolize hormones decreases. This can result in changes to estrogen and testosterone levels in the body. Symptoms of these changes include loss of pubic hair and the development of spider angiomas, small clusters of red blood vessels on the skin of the upper body, in both males and females. Men sometimes experience a decrease of testicular size and development of breast tissue (a condition called gynecomastia). A decline in the body's ability to metabolize medications means that normal doses can turn into toxic levels. Therefore, doses of medicines are often reduced for people who have liver disease.
• Regulation of glucose levels. Loss of liver cells leads to poorly controlled glucose levels. Glucose levels may soar after eating (hyperglycemia) or fall dangerously low between meals (hypoglycemia). This poor regulation of blood sugar is due to a different mechanism than the mechanisms that lead to diabetes types I and II.
• Conversion of ammonia, a by-product of metabolism, into a less toxic form called urea. Inability to convert ammonia to urea results in elevated ammonia levels in the blood. This can result in a condition called hepatic encephalopathy, which is a neurological syndrome characterized by alterations in mental status and behavior. Although acute episodes can be reversible, severe cases of hepatic encephalopathy can lead to coma and death.

Role in human health

A healthy liver enables the human body to:

• produce energy when needed
• manufacture new proteins
• store certain vitamins, minerals, and sugars
• regulate transport of fat stores
• regulate blood clotting
• facilitate the digestive process by producing bile
• control the production and excretion of cholesterol
• neutralize and destroy toxic substances
• metabolize alcohol
• monitor proper chemical and drug blood levels
• cleanse the blood and discharging waste products into the bile
• maintain hormone balance
• serve as the main fetal blood forming organ
• resist infection
• regenerate its damaged tissue
• store iron

Common diseases and disorders

Symptoms and signs of liver disease:

• jaundice, or abnormal yellowing of the skin and eyes (often the first, and may be the only, sign of liver disease)
• dark urine
• gray, yellow, or light colored stools
• nausea, vomiting, and/or loss of appetite
• intestinal bleeding due to liver diseases obstructing blood flow. (Bleeding may result in vomiting of blood, and bloody or black stools.)
• abdominal swelling (Liver disease may cause ascites, an accumulation of fluid in the abdominal cavity.)
• prolonged generalized itching
• an increase or decrease of more than 5% body weight in two months
• abdominal pain
• sleep disturbances, mental confusion, and coma that may result from an accumulation of toxic substances that impair brain function
• fatigue or loss of stamina
• loss of sexual drive or diminished performance

The most common liver diseases are as follows:

Viral hepatitis

• Hepatitis A spreads through contaminated water and food.
• Hepatitis B may be transmitted through transfusions, cuts, kissing, tooth brushing, ear piercing, tattooing, dental work, or during sexual contact.
• Hepatitis C primarily spreads through infected blood.

The liver often becomes tender and enlarged, and the patient usually experiences fever, weakness, nausea, vomiting, jaundice, and aversion to food. The virus may be present in the bloodstream, intestines, feces, saliva, and other body secretions. Hepatitis is common in the United States and some forms of it can be extremely infectious. Most people recover from viral forms of the disease without treatment, but some die and others may develop a chronic, disabling illness. In the United States there are more than four million hepatitis carriers.

Alcohol-related liver disorders

Liver disorders related to alcohol include fatty liver, alcoholic hepatitis, and alcoholic cirrhosis.

Fatty liver, the most common alcohol-related liver disorder, causes liver enlargement and abdominal discomfort. Swollen livers are often tender or painful, and may cause jaundice and liver function abnormalities.

Alcoholic hepatitis often results in nausea, vomiting, abdominal pain, fever, jaundice, liver enlargement and tenderness, and white blood cell count elevation. At times alcoholic hepatitis may be asymptomatic.

Cirrhosis

Over 25,000 Americans die from cirrhosis each year. It is the seventh leading cause of death. Among those 25-44, it is the fourth disease-related cause of death. Cirrhosis of the liver occurs when damaged liver cells are replaced by scar tissue causing diminished blood flow, which causes additional liver cell death. Loss of liver function results in gastrointestinal disturbances, emaciation, liver and spleen enlargement, jaundice, fluid accumulation in the abdomen and other tissues. Obstructed circulation often causes massive vomiting of blood.

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KEY TERMS

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Ascites—Accumulation of fluid in the abdominal cavity.

Bile—Yellowish substance released by the liver into the intestines to digest fats.

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Any severe liver injury may cause cirrhosis. Over half of the deaths from cirrhosis result from alcohol abuse, hepatitis, and other viruses. Toxins, chemicals, excessive iron or copper, severe drug reactions, and bile duct obstruction may also cause cirrhosis.

Gallstones

Gallstones form when cholesterol and/or pigment in bile crystallize into gall stones. Gall stones vary in size from small pebbles to golf balls. Occasionally gallstones become lodged in the bile ducts leading from the gall-bladder to the duodenum (first part of the small intestine). This may cause extreme abdominal pain. When gall stones block bile ducts, bile cannot flow into the intestines, and backs up into the bloodstream causing jaundice.

Gallstones are more common in people over 40, especially among women and the obese. Each year in the United States, 400-500,000 gallbladders are surgically removed.

Children's liver disorders

Tens of thousands of American children contract liver diseases causing hundreds of deaths each year. The most common of these diseases are:

Biliary atresia is caused by the lack, or inadequate size, of bile ducts connecting the liver to the intestine. Unable to excrete bile, death results from cirrhosis and bleeding by two years of age.

Chronic active hepatitis destroys liver cells replacing them with scar tissue. It is caused by an unknown process that resembles an allergy to the child's own liver tissue.

Galactosemia, an inherited disease, is caused by the lack of an enzyme needed to digest milk sugar. As a result, milk sugar accumulates in the liver and other organs, leading to cirrhosis of the liver, cataracts, and brain damage.

Wilson's disease occurs when copper accumulates in the liver due to an inherited abnormality, causing cirrhosis and brain damage.

Reyes syndrome is a fatal disorder in which fat accumulates in the liver.

Cirrhosis may result from extensive liver injury.

Liver cancer

Most liver cancer results from the spread of cancer from other organs to the liver (metastasis).

Bill Asenjo, MS, CRC