The liver is one of the body’s largest and most important organs. Located in the upper right part of the abdomen, beneath the diaphragm and partly protected by the lower ribs, it performs hundreds of jobs that keep the body supplied with energy, process nutrients, regulate chemicals in the blood, and help protect against harmful substances.
Unlike organs that mainly perform one recognizable task, such as pumping blood or moving food through the digestive tract, the liver functions as a central processing and storage organ. It receives nutrients absorbed from the intestines, modifies and stores some of them, makes essential proteins, produces bile for digestion, and breaks down many substances the body needs to remove.
The liver’s main jobs
The liver has several closely connected roles. Among the most important are processing nutrients, producing bile, making blood proteins, regulating blood glucose, storing certain nutrients, and chemically processing drugs and other substances.
Most of the liver’s work takes place inside specialized cells called hepatocytes. Blood from the digestive organs reaches the liver through the portal vein, bringing nutrients and other absorbed substances with it. The liver then processes this incoming material before it enters the rest of the circulation.
It processes nutrients from food
After you eat, carbohydrates, proteins, fats, vitamins, minerals, and other substances are absorbed through the digestive tract. Much of the nutrient-rich blood from the intestines travels directly to the liver.
The liver helps decide how these nutrients will be used, stored, or transformed. For example, it can convert certain nutrients into forms the body can use immediately, store them for later, or use them as raw materials for other molecules.
The liver is particularly important in handling the three major macronutrients:
- Carbohydrates: The liver stores glucose as glycogen and can release glucose into the bloodstream when the body needs more fuel. It can also make glucose from certain non-carbohydrate substances.
- Fats: The liver helps process fatty acids and cholesterol and participates in the production and transport of fats in the body.
- Proteins: The liver processes amino acids and uses them to make many proteins needed throughout the body. It also converts ammonia, a potentially toxic byproduct of protein metabolism, into urea, which the kidneys can remove in urine.
This metabolic work helps keep the composition of the blood within a useful range even as food intake and energy demands change.
It helps control blood sugar
The liver acts as an important buffer for blood glucose.
When blood glucose is plentiful, the liver can take up glucose and store it as glycogen, a readily accessible form of stored carbohydrate. When blood glucose falls, the liver can break down glycogen and release glucose into the bloodstream.
The liver can also make glucose through gluconeogenesis, using substances such as lactate, glycerol, and certain amino acids. This becomes especially important between meals and during prolonged periods without food.
Hormones, particularly insulin and glucagon, help coordinate these changes. Insulin generally promotes glucose storage and use after eating, while glucagon signals the liver to make more glucose available when blood sugar is low.
It produces bile for digestion
The liver makes bile, a fluid that is stored and concentrated in the gallbladder between meals and released into the small intestine when needed.
Bile contains bile acids or bile salts that help the digestive system handle dietary fat. They break large fat droplets into smaller ones, making it easier for digestive enzymes to act on the fat. This process also helps the intestine absorb fat-soluble vitamins such as vitamins A, D, E, and K.
Bile also provides a route for the body to eliminate certain substances, including bilirubin and excess cholesterol.
The gallbladder therefore works closely with the liver, but it does not make bile. The liver produces bile; the gallbladder stores and releases it.
It makes proteins that the body needs
The liver manufactures many proteins that circulate in the blood.
One important example is albumin, which helps maintain the proper distribution of fluid between the bloodstream and surrounding tissues. Albumin also carries various substances through the blood.
The liver also produces many proteins involved in blood clotting. These proteins are essential for stopping bleeding after an injury.
Because of this, significant liver dysfunction can affect both fluid balance and the body’s ability to form blood clots normally.
It processes drugs, alcohol, and other chemicals
The liver chemically modifies many substances so they can be used, inactivated, or eliminated from the body. This includes numerous medications, alcohol, hormones, and compounds produced during normal metabolism.
A large part of this work occurs through enzyme systems inside liver cells. Some substances are transformed into more water-soluble compounds that can then be excreted in urine or bile.
This is sometimes described as the liver “detoxifying” the body, but that phrase can be misleading. The liver does not simply remove every toxin from the bloodstream. Instead, it chemically transforms specific substances through metabolic reactions, and some of those reactions can themselves produce intermediate compounds that require further processing.
The way the liver handles a substance also depends on the substance, the dose, and individual factors such as genetics, other medications, and liver health.
It helps remove waste from the blood
The liver contributes to the removal and processing of several waste products.
One important example is bilirubin, a yellow pigment produced when the body breaks down old red blood cells. The liver takes up bilirubin, processes it, and secretes it into bile. It ultimately leaves the body through the digestive tract.
The liver also converts ammonia into urea. Ammonia is generated when amino acids are broken down and can be harmful at high levels, particularly to the brain. Urea is much less toxic and can be carried in the blood to the kidneys for excretion.
These processes illustrate an important feature of liver function: the liver often does not simply discard a substance. It transforms it into a form that another organ can safely eliminate.
It stores important nutrients
The liver serves as a storage site for several substances.
It stores glucose in the form of glycogen and can store significant amounts of certain vitamins and minerals, including iron and copper. These reserves can be drawn upon when the body needs them.
The liver’s storage function is closely tied to its metabolic role. Rather than acting as a passive warehouse, it continually adjusts what is stored and what is released according to the body’s needs.
It contributes to immune defense
The liver also helps filter material arriving from the digestive tract.
Specialized immune cells called Kupffer cells, located within the liver’s blood-filtering system, can engulf and help remove certain bacteria, damaged cells, and other foreign material from the blood.
The liver also produces proteins involved in immune and inflammatory responses. Its location between much of the digestive tract and the general circulation makes this protective role particularly important.
It helps regulate cholesterol
The liver plays a central role in cholesterol metabolism. It makes cholesterol, takes it up from the blood, converts some cholesterol into bile acids, and secretes cholesterol into bile.
Cholesterol itself is not inherently harmful. The body needs it for cell membranes, steroid hormones, and other functions. The problem arises when cholesterol transport and metabolism become abnormal, contributing to conditions such as atherosclerosis.
The liver’s handling of cholesterol is therefore part of a larger system involving the intestines, bloodstream, and other tissues.
How blood reaches the liver
The liver has a distinctive blood supply that reflects its role in processing what enters the body through the digestive system.
It receives blood from two major sources. The hepatic artery supplies oxygen-rich blood, while the hepatic portal vein carries nutrient-rich blood from the stomach, intestines, pancreas, and spleen.
Inside the liver, these blood supplies flow through specialized channels called sinusoids. Hepatocytes are positioned alongside these channels, allowing them to take up nutrients and other substances from the blood and release processed substances back into circulation.
Blood then leaves the liver through the hepatic veins and returns to the heart.
This arrangement allows the liver to process many substances absorbed from a meal before they circulate throughout the body.
What happens when the liver is damaged?
The liver has a remarkable ability to repair itself after some forms of injury. But persistent or severe damage can interfere with its many functions.
Liver injury can result from numerous causes, including certain viral infections, long-term excessive alcohol exposure, metabolic dysfunction associated with excess fat accumulation, autoimmune disease, inherited disorders, and some medications or toxic substances.
Chronic injury can lead to fibrosis, in which scar tissue accumulates. Advanced, extensive scarring is called cirrhosis. As normal liver tissue is progressively replaced by scar tissue and the liver’s architecture becomes distorted, its ability to perform essential functions can decline.
The consequences depend on which functions are affected and how advanced the disease is. Problems can include abnormal bleeding, accumulation of fluid, impaired processing of bilirubin, changes in blood chemistry, reduced production of essential proteins, and buildup of substances that the damaged liver can no longer process effectively.
Some liver diseases cause few or no noticeable symptoms in their early stages, which is one reason liver problems can remain undetected for a long time.
The liver works as part of a larger system
It is tempting to think of the liver as a standalone “filter,” but that description leaves out much of what makes the organ important.
The liver works continuously with the digestive tract, pancreas, gallbladder, kidneys, immune system, and circulatory system. The intestines supply it with absorbed nutrients; the pancreas and hormones help regulate nutrient metabolism; the gallbladder delivers liver-produced bile when needed; and the kidneys remove many of the water-soluble products that the liver has processed.
Its central role is therefore less about one specific task than about maintaining the body’s internal chemical environment. The liver takes in nutrients, metabolic products, hormones, medications, and other compounds; transforms or stores them as appropriate; produces substances the body needs; and directs many waste products toward elimination.
That combination of metabolic control, synthesis, storage, digestion, immune defense, and chemical processing is what makes the liver indispensable to normal human physiology.
