The human liver is the largest solid internal organ in the body, performing a wide range of processes indispensable for life. As both an endocrine and exocrine organ, its activities are complex. It handles over 500 tasks, which impacts overall health and bodily regulation.
Liver Anatomy and Location
The liver is in the upper right portion of the abdominal cavity, beneath the diaphragm and above the stomach and intestines. This dark reddish-brown, cone-shaped organ weighs about three pounds in an adult. It holds approximately one pint of the body’s blood at any given time, about 13% of the total supply, and is enclosed in a fibrous layer called Glisson’s capsule.
The liver is divided into a large right lobe and a smaller left lobe, with two smaller accessory lobes, the caudate and quadrate. These lobes are organized into eight segments, composed of thousands of smaller functional units called lobules. The lobules connect to small ducts that channel bile toward the larger common hepatic duct.
The liver has a dual blood supply. It receives oxygenated blood from the hepatic artery, accounting for about 20-25% of its blood flow. The remaining 75-80% comes from the hepatic portal vein, which transports nutrient-rich blood from the digestive system for processing.
Key Functions of the Liver
Metabolism
The liver is a center for the body’s metabolic processes, managing carbohydrates, fats, and proteins from the digestive tract. It regulates blood sugar by converting excess glucose into glycogen for storage. When energy is needed, the liver breaks down glycogen into glucose (glycogenolysis) or creates new glucose from substances like amino acids (gluconeogenesis).
For fat metabolism, the liver synthesizes cholesterol, triglycerides, and lipoproteins that transport fats. In protein metabolism, it synthesizes blood proteins like albumin and processes amino acids. The liver also converts ammonia, a toxic byproduct of protein metabolism, into urea for excretion in urine.
Detoxification and Filtration
The liver’s most recognized role is filtering and detoxifying the blood. All blood from the stomach and intestines passes through the liver, where it processes drugs, alcohol, and toxins into less harmful forms for excretion. This process, known as drug metabolism, can involve making substances more water-soluble for removal via urine or bile.
The liver also removes internal waste, breaking down hormones like insulin after use to maintain hormonal balance. Specialized Kupffer cells remove bacteria and pathogens from the bloodstream, contributing to immune defense. The byproducts of detoxification are released into the blood for the kidneys to filter or are excreted into bile.
Production
The liver manufactures several substances, most prominently bile. This alkaline fluid aids digestion by breaking down and absorbing fats and fat-soluble vitamins in the small intestine. Bile also carries waste products away from the liver for elimination.
The liver synthesizes most blood plasma proteins. Albumin, the most abundant, maintains fluid balance in blood vessels and transports various substances. The liver also produces most clotting factors, like prothrombin and fibrinogen, which are necessary for blood coagulation.
Storage
The liver acts as a storage depot for nutrients. It stores glucose as glycogen, a ready energy source that can be released to maintain stable blood sugar levels between meals.
The liver also stores important vitamins and minerals. It is a primary storage site for fat-soluble vitamins A, D, E, and K. The liver also stores iron (as ferritin) and copper, regulating their levels to prevent deficiency or toxic accumulation.
Common Liver Conditions
Several conditions can affect the liver, developing from lifestyle factors, viruses, or other health issues. Non-alcoholic fatty liver disease (NAFLD) is the accumulation of excess fat in liver cells not caused by alcohol. It is linked to obesity, type 2 diabetes, and high cholesterol. A more serious form, nonalcoholic steatohepatitis (NASH), involves inflammation and cell damage that can lead to scarring.
Alcohol-associated liver disease results from heavy alcohol use, which damages liver cells and causes inflammation. The earliest stage is alcoholic fatty liver, a reversible fat buildup. Continued drinking can lead to more severe damage, including alcoholic hepatitis (inflammation) and cirrhosis.
Hepatitis is inflammation of the liver, commonly caused by a viral infection. Chronic hepatitis B or C infections can lead to long-term inflammation and significant liver damage. Cirrhosis is the advanced stage of liver disease where extensive scar tissue replaces healthy tissue. This scarring, resulting from long-term damage from conditions like chronic hepatitis or alcohol abuse, impairs the liver’s function.
The Liver’s Regenerative Ability
The liver has a unique capacity to regenerate its own damaged tissue. This process is driven by the proliferation of its main cells, hepatocytes. After an injury or surgical removal of a portion of the liver, mature hepatocytes can divide to restore the organ’s mass and function. This response is a highly regulated process involving growth factors and cytokines.
This regenerative ability is substantial but not infinite, as it depends on the health of the remaining tissue. In cases of chronic injury from long-term alcohol misuse or viral infections, the process can be overwhelmed. This constant cycle of damage and repair leads to scar tissue formation instead of healthy cells, which defines cirrhosis and permanently compromises liver function.
Maintaining Liver Health
Protecting the liver involves lifestyle choices that reduce its workload. Maintaining a healthy weight through a balanced diet and regular physical activity helps prevent non-alcoholic fatty liver disease. A diet rich in fruits, vegetables, and whole grains that limits salt, sugar, and saturated fats supports liver function.
Limiting alcohol consumption protects the liver, as heavy drinking is a primary cause of cell damage and inflammation. For those with existing liver conditions, abstaining from alcohol is recommended to prevent further harm. It is also important to use medications cautiously, as many are processed by the liver.
Preventive measures include vaccination against viruses that can harm the liver. Vaccines are available for hepatitis A and hepatitis B, which can cause acute and chronic liver disease. People with chronic liver conditions are encouraged to get vaccinated, as another viral infection can lead to more severe outcomes.