The liver is the largest internal organ in the human body, a dark reddish-brown, cone-shaped structure weighing about 3 pounds. It sits in the upper right portion of your abdominal cavity, tucked beneath the diaphragm and resting on top of the stomach, right kidney, and intestines. The word itself traces back to Old English “lifer,” closely linked to the word “life,” reflecting how ancient peoples recognized this organ as essential to survival. That instinct was correct: the liver performs over 500 functions that keep you alive.
Where the Word Comes From
In some of the oldest English dictionaries, “liver” doesn’t even have its own entry. Instead, it appears under the word “life,” defined as the bile-secreting organ derived from Old English “lifer.” The word has cousins across Germanic languages: Old Norse “lifr,” Dutch “lever,” and German “Leber,” all tracing back to a shared root. Etymologists connect it to an ancient root meaning “to stick” or “fat,” though not everyone agrees on the exact lineage. What is clear is the tight bond between “liver” and “to live.” Across cultures and centuries, the liver was seen as the seat of courage and existence itself.
What the Liver Actually Does
The liver consists of two main lobes and functions as a chemical processing plant for nearly everything that enters your body. Its roles fall into a few major categories: managing blood sugar, digesting fats, filtering toxins, and building essential proteins.
Blood Sugar Regulation
Your liver acts as a fuel reservoir, keeping blood sugar levels steady whether you just ate a large meal or haven’t eaten in 12 hours. After a meal, when insulin levels are high, the liver converts excess glucose into a storage form called glycogen and tucks it away. Between meals and overnight, it reverses the process, breaking glycogen back into glucose and releasing it into your bloodstream. When glycogen stores run low, the liver can manufacture glucose from scratch using amino acids, fat byproducts, and other raw materials.
Bile and Fat Digestion
The liver produces between 800 and 1,000 milliliters of bile every day, roughly a quart. Bile’s main job is to break large fat globules in your food into smaller particles so your intestines can absorb them. Without this step, your body would struggle to process dietary fats or absorb fat-soluble vitamins like A, D, E, and K. Bile is stored in the gallbladder between meals and released when fatty food arrives in the small intestine.
Filtering Toxins
Everything absorbed from your digestive tract passes through the liver before reaching the rest of your body. The liver neutralizes harmful substances in two stages. First, enzymes chemically alter a toxic molecule, often making it more reactive in the short term. Then, in the second stage, liver cells attach a small molecule (like a sulfur compound or an amino acid) to that intermediate product, converting it into something water-soluble and far less harmful. Your kidneys can then flush it out through urine. This two-stage system handles everything from alcohol and medications to environmental pollutants.
Protein Production
The liver synthesizes nearly all the major proteins circulating in your blood. It is the sole producer of albumin, the protein responsible for keeping fluid balanced in your blood vessels and tissues. It also manufactures fibrinogen, prothrombin, and other clotting factors that stop you from bleeding when you’re cut. In total, the liver produces 17 major plasma proteins. It even makes a hormone that tells your bone marrow how many platelets to produce.
The Liver Can Regrow Itself
One of the liver’s most remarkable traits is its ability to regenerate. Surgeons can remove up to two-thirds of the organ, and the remaining tissue will regrow to restore the original mass, typically within about two weeks in animal models. This happens through a combination of existing liver cells dividing and individual cells increasing in size. Even when 80 to 90 percent of the liver is removed, a backup system kicks in: cells lining the bile ducts revert to a more primitive state and repopulate the organ. No other internal organ in the human body can do this at the same scale.
Signs the Liver Isn’t Working Well
Because the liver handles so many jobs quietly, problems often go unnoticed until significant damage has occurred. The most recognizable sign is jaundice, a yellowing of the skin and whites of the eyes caused by a buildup of bilirubin, a yellow pigment the liver normally processes and clears. When liver cells are damaged, bilirubin accumulates in the blood.
Other symptoms of liver trouble include pain or tenderness in the upper right abdomen, a swollen belly from fluid accumulation (called ascites), nausea, confusion or disorientation, persistent fatigue, and breath that smells musty or unusually sweet. Tremors and excessive sleepiness can appear in more advanced cases.
How Common Liver Disease Has Become
Fatty liver disease, now the most common liver condition worldwide, affects an estimated 32 percent of adults globally. That number has been climbing: studies from 2005 or earlier found a prevalence of about 26 percent, while studies from 2016 onward found 38 percent. Men are affected more often than women, at roughly 40 percent versus 26 percent. The condition develops when fat builds up in liver cells, often driven by excess weight, insulin resistance, or a high-sugar diet, and it can progress to inflammation and scarring over time.
What Liver Blood Tests Measure
If your doctor orders liver function tests, two of the most common markers are ALT and AST. These are enzymes normally present inside liver cells in small amounts. When liver cells are injured, they leak into the bloodstream, causing levels to rise. Normal ALT ranges from 7 to 55 units per liter, and normal AST ranges from 8 to 48 units per liter. Elevated numbers don’t point to a specific disease on their own, but they signal that something is stressing or damaging liver tissue and typically prompt further investigation.
AST can also rise from muscle damage, so it’s less specific to the liver than ALT. Doctors usually look at the ratio between the two, along with other markers like bilirubin and albumin levels, to get a fuller picture of how well the liver is functioning.