The liver is your body’s largest internal organ, weighing about 3 pounds and sitting in the upper right portion of your abdomen, just beneath the diaphragm. It performs over 500 functions, but they cluster around a handful of critical jobs: filtering your blood, processing nutrients, making essential proteins, storing energy, producing digestive fluid, and defending against infection. No artificial device can replicate everything the liver does, which is why severe liver failure is life-threatening within days.
Turning Food Into Fuel
After you eat, your digestive system breaks food into simple sugars, amino acids, and fatty acids. These travel through the bloodstream directly to the liver via a dedicated blood vessel called the portal vein. The liver then decides what to do with each molecule based on what your body needs at that moment.
When blood sugar rises after a meal, the liver pulls glucose out of the blood and packages it into a storage molecule called glycogen. A healthy liver holds roughly 70 to 100 grams of glycogen, enough to keep your brain and muscles running for several hours. When blood sugar drops between meals or during exercise, the liver breaks glycogen back down into glucose and releases it. During prolonged exercise lasting more than about 40 minutes, glycogen stores start running low. At that point, the liver shifts to building new glucose from scratch using amino acids, lactate, and other raw materials. This is why your liver matters even when you haven’t eaten in hours: it’s the organ that keeps your blood sugar stable around the clock.
The liver also processes fats and amino acids from protein. It packages fats into forms other tissues can use for energy, and it converts excess amino acids into usable fuel while safely disposing of the nitrogen waste they leave behind (as urea, which your kidneys then filter out).
Filtering Toxins From Your Blood
Everything absorbed from your gut, along with medications, alcohol, and environmental chemicals, passes through the liver before reaching the rest of your body. The liver neutralizes harmful substances in two stages.
In the first stage, a family of enzymes breaks down toxins into intermediate compounds. These enzymes are the same ones that process alcohol, caffeine, and most prescription drugs. The intermediates are sometimes more reactive than the original substance, which is why the second stage matters so much. In that stage, the liver attaches a water-friendly molecule (like glutathione, sulfate, or glycine) to each intermediate, making it dissolve in water so your kidneys or bile can flush it out of the body.
This two-stage system is remarkably adaptable. If you’re regularly exposed to a particular substance, the liver can ramp up production of the specific enzymes needed to process it. That adaptability is also why certain medications interact with each other: two drugs competing for the same set of enzymes can alter how quickly each one is cleared.
Producing Bile for Digestion
The liver produces between 800 and 1,000 milliliters of bile every day. Bile is a yellow-green fluid stored in the gallbladder and released into your small intestine when you eat fatty foods. Its most important components, bile salts, act like a detergent: they break large fat droplets into tiny ones so digestive enzymes can access them. Without bile, your body can’t efficiently absorb dietary fats or the fat-soluble vitamins (A, D, E, and K) that dissolve in them.
Bile also serves as one of the liver’s waste disposal routes. Bilirubin, a byproduct of old red blood cells being recycled, gets excreted through bile. It’s what gives stool its brown color. When the liver can’t process bilirubin properly, it builds up in the blood and turns the skin and eyes yellow, a condition called jaundice.
Making Proteins Your Blood Depends On
The liver manufactures many of the proteins circulating in your bloodstream. Albumin is the most abundant, and it does two essential things: it carries hormones, drugs, and other molecules through the blood, and it maintains the fluid balance between your blood vessels and surrounding tissues. When albumin levels drop because of liver damage, fluid leaks into the abdomen and legs, causing visible swelling.
The liver also produces the majority of clotting factors, the proteins that stop bleeding when you’re injured. These clotting factors have a short lifespan in the blood, so the liver has to keep making them continuously. When liver function declines sharply, clotting slows down and even minor injuries can bleed longer than normal. This is one of the earliest measurable signs of serious liver trouble.
Storing Vitamins and Minerals
Your liver acts as a warehouse for several nutrients that your body needs in steady amounts but doesn’t absorb at a constant rate. It stores vitamins A, B12, D, E, and K, along with the minerals iron and copper. Vitamin A stores, for instance, can last months. Vitamin B12 stores can sustain you for years. This buffering system means that short-term gaps in your diet don’t immediately cause deficiency symptoms, because the liver releases its reserves to fill the gap.
Iron storage is especially important. The liver holds iron in a protein called ferritin and releases it when your bone marrow needs to produce new red blood cells. When the liver is damaged by disease, iron metabolism can go haywire, leading to either dangerous iron buildup or deficiency.
Acting as an Immune Organ
The liver sits at a strategic checkpoint. Blood flowing from the intestines carries not only nutrients but also bacteria, bacterial fragments, and other foreign material that slipped through the gut lining. The liver contains the body’s largest population of tissue-based immune cells, called Kupffer cells. These specialized cells engulf and destroy bacteria, viruses, and dead cells before they can spread to the rest of the body.
Kupffer cells manage this without triggering widespread inflammation, which is a delicate balancing act. They’re constantly exposed to low levels of bacterial material from the gut and have learned to clean it up quietly. During an actual infection, though, they shift into a more aggressive mode. In bacterial infections, Kupffer cells capture and kill the invading organisms, sometimes sacrificing themselves in the process. This frontline defense is one reason liver damage raises the risk of serious bloodstream infections.
Regenerating After Injury
The liver is the only internal organ that can regrow after major tissue loss. If up to 70% of the liver is removed surgically, the remaining cells receive a cascade of chemical signals within minutes. Growth factors push resting liver cells back into the cell cycle, and they begin dividing to restore the organ’s original mass. This process involves both an increase in cell number and an increase in individual cell size.
This regenerative ability makes living-donor liver transplants possible: a healthy person can donate a portion of their liver, and both the donor’s and recipient’s portions grow back toward full size. However, regeneration has limits. Chronic damage from years of heavy drinking, viral hepatitis, or metabolic disease can outpace the liver’s ability to repair itself. Scar tissue (fibrosis) replaces functional cells, eventually leading to cirrhosis, where the liver becomes too stiff and scarred to work properly.
What Happens When the Liver Struggles
Because the liver handles so many jobs simultaneously, damage tends to show up in multiple ways at once. Early liver disease often produces no symptoms at all. As function declines, signs like persistent fatigue, easy bruising, swelling in the legs or abdomen, dark urine, and yellowing skin start to appear.
The most common form of liver disease today is metabolic dysfunction-associated steatotic liver disease, or MASLD (previously called nonalcoholic fatty liver disease). It develops when excess fat accumulates in liver cells, typically alongside risk factors like obesity, high blood sugar, or high blood pressure. In some people, this fat buildup triggers ongoing inflammation, a stage now called MASH, which can progress to fibrosis and cirrhosis over years. MASLD affects an estimated one in four adults worldwide, and most don’t know they have it because the early stages are silent.
Alcohol-related liver disease follows a similar path, from fat accumulation to inflammation to scarring, but is driven by heavy or prolonged alcohol use rather than metabolic factors. Viral hepatitis B and C can also cause chronic liver inflammation leading to cirrhosis or liver cancer if untreated.