The liver is the largest solid organ and the largest gland in the human body. It carries out over 500 essential tasks.
Classed as part of the digestive system, the roles of the liver include detoxification, protein synthesis, and the production of chemicals that help digest food.
This MNT Knowledge Center article will cover the main roles of the liver, how the liver regenerates, what happens when the liver does not function correctly, and how to keep the liver healthy.
Fast facts on the liver
- The liver is classed as a gland.
- This vital organ carries out more than 500 roles in the human body.
- It is the only organ that can regenerate.
- The liver is the largest solid organ in the body.
- Alcohol abuse is one of the major causes of liver problems in the industrialized world.
Weighing between 3.17 and 3.66 pounds (lb), or between 1.44 and 1.66 kilograms (kg), the liver is reddish-brown with a rubbery texture. It is situated above and to the left of the stomach and below the lungs.
The skin is the only organ heavier and larger than the liver.
The liver is roughly triangular and consists of two lobes: a larger right lobe and a smaller left lobe. The lobes are separated by the falciform ligament, a band of tissue that keeps it anchored to the diaphragm.
A layer of fibrous tissue called Glisson's capsule covers the outside of the liver. This capsule is further covered by the peritoneum, a membrane that forms the lining of the abdominal cavity.
This helps hold the liver in place and protects it from physical damage.
Unlike most organs, the liver has two major sources of blood. The portal vein brings in nutrient-rich blood from the digestive system, and the hepatic artery carries oxygenated blood from the heart.
The blood vessels divide into small capillaries, with each ending in a lobule. Lobules are the functional units of the liver and consist of millions of cells called hepatocytes.
Blood is removed from the liver through three hepatic veins.
The liver is classed as a gland and associated with many functions. It is difficult to give a precise number, as the organ is still being explored, but it is thought that the liver carries out 500 distinct roles.
The major functions of the liver include:
- Bile production: Bile helps the small intestine break down and absorb fats, cholesterol, and some vitamins. Bile consists of bile salts, cholesterol, bilirubin, electrolytes, and water.
- Absorbing and metabolizing bilirubin: Bilirubin is formed by the breakdown of hemoglobin. The iron released from hemoglobin is stored in the liver or bone marrow and used to make the next generation of blood cells.
- Supporting blood clots: Vitamin K is necessary for the creation of certain coagulants that help clot the blood. Bile is essential for vitamin K absorption and is created in the liver. If the liver does not produce enough bile, clotting factors cannot be produced.
- Fat metabolization: Bile breaks down fats and makes them easier to digest.
- Metabolizing carbohydrates: Carbohydrates are stored in the liver, where they are broken down into glucose and siphoned into the bloodstream to maintain normal glucose levels. They are stored as glycogen and released whenever a quick burst of energy is needed.
- Vitamin and mineral storage: The liver stores vitamins A, D, E, K, and B12. It keeps significant amounts of these vitamins stored. In some cases, several years' worth of vitamins is held as a backup. The liver stores iron from hemoglobin in the form of ferritin, ready to make new red blood cells. The liver also stores and releases copper.
- Helps metabolize proteins: Bile helps break down proteins for digestion.
- Filters the blood: The liver filters and removes compounds from the body, including hormones, such as estrogen and aldosterone, and compounds from outside the body, including alcohol and other drugs.
- Immunological function: The liver is part of the mononuclear phagocyte system. It contains high numbers of Kupffer cells that are involved in immune activity. These cells
destroy any disease-causing agentsthat might enter the liver through the gut.
- Production of albumin: Albumin is the most common protein in blood serum. It transports fatty acids and steroid hormones to help maintain the correct pressure and prevent the leaking of blood vessels.
- Synthesis of angiotensinogen: This hormone raises blood pressure by narrowing the blood vessels when alerted by production of an enzyme called renin in the kidneys.
Because of the importance of the liver and its functions, evolution has ensured that it can regrow rapidly as long as it is kept healthy. This ability is seen in all vertebrates from fish to humans.
The liver is the only visceral organ that can regenerate.
It can regenerate completely, as long as a minimum of 25 percent of the tissue remains. One of the most impressive aspects of this feat is that the liver can regrow to its previous size and ability without any loss of function during the growth process.
In mice, if two-thirds of the liver is removed, the remaining liver tissue can regrow to its original size within 5 to 7 days. In humans, the process takes slightly longer, but regeneration can still occur in 8 to 15 days - an incredible achievement, given the size and complexity of the organ.
Over the following few weeks, the new liver tissue becomes indistinguishable from the original tissue.
This regeneration is helped by a number of compounds, including growth factors and cytokines. Some of the most important compounds in the process appear to be:
- hepatocyte growth factor
- transforming growth factor-alpha
- epidermal growth factor
An organ as complex as the liver can experience a range of problems. A healthy liver functions very efficiently. However, in a diseased or malfunctioning liver, the consequences can be dangerous or even fatal.
Examples of liver disease include:
Fascioliasis: This is caused by the parasitic invasion of a parasitic worm known as a liver fluke, which can lie dormant in the liver for months or even years. Fascioliasis is considered a tropical disease.
Cirrhosis: This sees scar tissue replace liver cells in a process known as fibrosis. This condition can be caused by a number of factors, including toxins, alcohol, and hepatitis. Eventually, fibrosis can lead to liver failure as the functionality of the liver cells is destroyed.
Hepatitis: Hepatitis is the name given to a general infection of the liver, and viruses, toxins, or an autoimmune response can cause it. It is characterized by an inflamed liver. In many cases, the liver can heal itself, but liver failure can occur in severe cases.
Primary sclerosing cholangitis (PSC): PSC is a serious inflammatory disease of the bile ducts that results in their destruction. There is currently no cure, and the cause is currently unknown, although the condition is thought to be autoimmune.
Fatty liver disease: This usually occurs alongside obesity or alcohol abuse. In fatty liver disease, vacuoles of fat build up in the liver cells. If it is not caused by alcohol abuse, the condition is called non-alcoholic fatty liver disease (NAFLD).
It is usually caused by genetics, medications, or a diet high in fructose sugar. It is the most common liver disorder in developed countries and has been associated with insulin resistance. Non-alcoholic steatohepatitis (NASH) is a condition that can develop if NAFLD gets worse. NASH is a known cause of liver cirrhosis.
Liver cancer: The most common types of liver cancer are hepatocellular carcinoma and cholangiocarcinoma. The leading causes are alcohol and hepatitis. It is the sixth most common form of cancer and the second most frequent cause of cancer death.
Below are some recommendations to help keep your liver working as it should:
- Diet: As the liver is responsible for digesting fats, consuming too many can overwork the organ and disturb it from other tasks. Obesity is also linked to fatty liver disease.
- Moderate alcohol intake: Avoid consuming more than two drinks at a time. Drinking too much alcohol causes cirrhosis of the liver over time. When the liver breaks down alcohol, it produces toxic chemicals, such as acetaldehyde and free radicals. For serious damage to occur, it takes the equivalent of a liter of wine every day for 20 years in men. For women, the threshold is less than half of that.
- Avoiding illicit substances: When last surveyed in 2012, close to 24 million people in the United States had consumed an illicit, non-medical drug within the last month. These can overload the liver with toxins.
- Caution when mixing medications: Some prescription drugs and natural remedies can interact negatively when mixed. Mixing drugs with alcohol puts significant pressure on the liver. For example, combining alcohol and acetaminophen can lead to acute liver failure. Be sure to follow the instructions on any medications.
- Protection against airborne chemicals: When painting or using strong cleaning or gardening chemicals, the area should be well ventilated, or a mask should be worn. Airborne chemicals can cause liver damage because the liver has to process any toxins that enter the body.
- Travel and vaccinations: Vaccination is essential if you are traveling to an area in which hepatitis A or B might be a concern. Malaria grows and multiplies in the liver, and yellow fever can lead to liver failure. Both diseases can be prevented by oral medication and vaccination.
- Safe sex: There is no vaccination for hepatitis C, so caution is advised in regards to safe sex, tattoos, and piercings.
- Avoid exposure to blood and germs: Receive medical attention if you are exposed to the blood of another person. It is also important not to share personal items related to hygiene, such as toothbrushes, and to avoid dirty needles.
Despite its ability to regenerate, the liver depends on being healthy to do so. The liver can mostly be protected through lifestyle choices and dietary measures.