Your liver performs over 500 functions, making it one of the hardest-working organs in your body. It filters your blood, regulates your energy supply, produces essential proteins, aids digestion, stores nutrients, and neutralizes harmful substances. Weighing about three pounds and sitting just under your right ribcage, it receives roughly 25% of your heart’s total blood output despite making up only 2.5% of your body weight.
Blood Sugar Regulation
One of the liver’s most critical jobs is keeping your blood sugar stable, whether you just ate a big meal or haven’t eaten in hours. After you eat, your liver converts excess glucose into a storage molecule called glycogen, packing it away for later use. When carbohydrates exceed what glycogen stores can hold, the liver converts the surplus into fat and ships it out for long-term storage in fat tissue.
Between meals, the process reverses. Rising levels of the hormone glucagon signal your liver to break stored glycogen back into glucose and release it into your bloodstream. This keeps your brain, muscles, and red blood cells fueled even when you’re sleeping or skipping a meal. After about 30 hours without food, glycogen stores run out entirely. At that point, the liver switches to manufacturing brand-new glucose from non-sugar raw materials, primarily lactate from muscles and glycerol released from fat tissue. This backup system is what keeps your blood sugar from crashing during prolonged fasting.
Detoxification in Two Stages
Your liver is the body’s primary detoxification center, neutralizing everything from alcohol and medications to environmental pollutants and the byproducts of normal metabolism. It does this through a two-stage process.
In the first stage, a large family of enzymes called cytochrome P450 chemically alters toxic compounds, adding oxygen to create a reactive site on the molecule. Think of this as “tagging” the toxin so it can be processed further. In the second stage, the liver attaches a water-soluble molecule to that reactive site, which makes the compound easy to dissolve and flush out through urine or bile. The liver uses several different water-soluble tags for this purpose, including compounds derived from amino acids, sulfur, and a powerful antioxidant called glutathione. Together, these two phases convert fat-soluble toxins that would otherwise accumulate in your tissues into water-soluble waste your kidneys and intestines can eliminate.
Bile Production and Fat Digestion
Your liver produces between 800 and 1,000 milliliters of bile every day. That’s roughly a quart of this yellow-green fluid, which gets stored and concentrated in your gallbladder until you eat a meal containing fat. Bile is a complex mixture of cholesterol, bile salts, water, bilirubin (a pigment from broken-down red blood cells), and various minerals including copper, potassium, and sodium.
Bile salts are the key ingredient. When bile enters your small intestine, these salts act like a detergent, breaking large fat droplets into tiny ones that mix with the watery environment of your gut. This process, called emulsification, gives digestive enzymes much more surface area to work with, allowing your body to absorb dietary fats and fat-soluble vitamins efficiently. Without adequate bile, fats pass through undigested, and you lose access to essential nutrients.
Protein Production
Your liver is a protein factory. It synthesizes albumin, the most abundant protein in your blood, which maintains fluid balance by keeping water from leaking out of blood vessels into surrounding tissues. When liver disease reduces albumin production, fluid accumulates in the abdomen and legs.
The liver also manufactures nearly every protein involved in blood clotting. It produces fibrinogen and clotting factors II, V, VII, IX, X, XI, and XII. Only one major clotting protein, von Willebrand factor, is made elsewhere (by the cells lining your blood vessels). This is why liver failure causes dangerous bleeding problems: the organ responsible for making the clotting machinery is compromised.
Immune Defense
Your liver contains specialized immune cells called Kupffer cells, which line the tiny blood vessels inside the organ and act as a biological filter. Because the liver receives blood directly from the intestines through the portal vein, these cells serve as the last checkpoint between your gut and the rest of your body. They capture and destroy bacteria, dead cells, and immune-reactive particles before those substances can reach general circulation.
Kupffer cells are the body’s most active phagocytes, meaning they physically engulf and digest foreign material. They also clear old and damaged red blood cells from the bloodstream. This function is so central to immunity that Kupffer cells make up the majority of what scientists call the mononuclear phagocytic system, the body’s main network of scavenging immune cells.
Hormone Clearance
Hormones are meant to deliver their message and then be removed. Your liver handles much of that cleanup. It is the primary site for metabolizing estrogen, breaking it down into various metabolites that can be excreted. The liver also clears insulin from the blood after it has done its job of lowering blood sugar. Changes in this insulin clearance rate directly affect how much insulin circulates in your body, and reduced clearance is linked to the high insulin levels seen in metabolic syndrome. Thyroid hormones, cortisol, and aldosterone are also processed and deactivated by the liver.
Nutrient Storage
Your liver acts as a warehouse for several vitamins and minerals your body needs but can’t always get from a single meal. It stores the fat-soluble vitamins A, D, E, and K. Vitamin A is held in specialized cells within the liver called Ito cells (also known as stellate cells). Vitamin E is repackaged and sent back into circulation attached to cholesterol-carrying particles. Vitamin K, while not stored in the liver long-term, is essential for a liver enzyme that activates clotting factors.
The liver also stores iron and copper, releasing them into the bloodstream as needed. Iron storage is particularly important because both too little and too much iron cause serious health problems, and the liver helps maintain the balance.
How to Tell If Your Liver Is Healthy
Liver function is typically assessed through a simple blood test that measures enzyme levels. Two of the most common markers are ALT (alanine aminotransferase) and AST (aspartate aminotransferase). For adult men, normal ALT ranges from 7 to 55 units per liter, and normal AST ranges from 8 to 48 units per liter. Women and children may have slightly different reference ranges. Elevated levels suggest liver cells are being damaged and leaking these enzymes into the bloodstream, though the degree of elevation helps distinguish between mild irritation and serious disease.
The Liver Can Regrow Itself
Perhaps the most remarkable thing about the liver is its ability to regenerate. Surgeons can remove up to 70% of a healthy liver, leaving just 30%, and the remaining tissue will grow back to nearly its original size. In many patients, this regrowth happens within a month of surgery. The new cells start out immature but quickly develop full function within days. This regenerative capacity is what makes living-donor liver transplants possible: a donor gives a portion of their liver, and both the donor’s and recipient’s portions grow back.
This ability has limits, though. Chronic damage from alcohol, viral hepatitis, or fatty liver disease can overwhelm the regeneration process, replacing healthy tissue with scar tissue (fibrosis) that eventually becomes cirrhosis. Once scarring is extensive, the liver loses its ability to bounce back.