The liver is made primarily of specialized cells called hepatocytes, which account for roughly 80% of the organ’s volume. These cells are organized into tiny hexagonal units, supported by connective tissue, and threaded with an extraordinary network of blood vessels and bile-collecting channels. In an average adult, the liver weighs between about 1,400 and 1,800 grams (roughly 3 to 4 pounds), though this varies with body size and sex.
Hepatocytes: The Main Building Block
Hepatocytes are the workhorse cells of the liver. They process nutrients absorbed from the gut, produce bile for fat digestion, store vitamins and minerals, break down toxins, and manufacture proteins the blood needs for clotting and immune defense. These cells are unusually versatile compared to most cells in the body, performing over 500 distinct functions.
What makes hepatocytes remarkable is their ability to regenerate. If a portion of the liver is removed or damaged, hepatocytes can divide and regrow the organ back to its functional size. This capacity is rare among internal organs and is one reason liver transplants from living donors are possible.
How Liver Tissue Is Organized
Under a microscope, liver tissue is arranged into repeating units called lobules, each shaped like a tiny hexagon. At the center of every lobule sits a small vein (the central vein), and at each corner sits a cluster of three structures known as the portal triad: a branch of the hepatic artery carrying oxygen-rich blood, a branch of the portal vein carrying nutrient-rich blood from the digestive tract, and a small bile duct that collects bile flowing in the opposite direction.
Between the rows of hepatocytes, narrow channels called sinusoids carry blood from the portal triads inward toward the central vein. These sinusoids are lined with specialized endothelial cells that have tiny pores, or fenestrations, allowing nutrients and oxygen to pass freely to the hepatocytes on either side. Embedded among these lining cells are Kupffer cells, a type of immune cell (macrophage) that filters bacteria, debris, and old blood cells out of the passing blood.
Running alongside the sinusoids but in the opposite direction are microscopic grooves called bile canaliculi. These tiny channels collect bile produced by hepatocytes and funnel it outward toward the bile ducts at the edges of each lobule. From there, bile travels through progressively larger ducts until it reaches the gallbladder for storage or flows directly into the small intestine.
The Liver’s Dual Blood Supply
The liver receives more blood than almost any other organ, roughly one liter per minute. What makes its blood supply unusual is that it comes from two separate sources. About 75% arrives through the portal vein, which carries blood that has already passed through the stomach and intestines. This blood is rich in glucose, amino acids, and fats but relatively low in oxygen. The remaining 25% comes from the hepatic artery, which delivers oxygen-rich blood directly from the heart. Despite supplying only a quarter of total blood flow, the hepatic artery provides more than half of the liver’s oxygen.
This dual supply is central to what the liver does. The portal vein delivers raw materials from digestion, and the hepatocytes process them before releasing the results into the body’s general circulation through the hepatic veins. It also means the liver is the first stop for anything absorbed from the gut, including medications and alcohol, which is why it bears the brunt of many toxic exposures.
Connective Tissue and the Outer Capsule
Wrapping the entire organ is a thin, tough layer called Glisson’s capsule, made of dense connective tissue composed mainly of type I collagen (the same structural protein found in tendons and skin). This capsule gives the liver its smooth surface and structural integrity, which matters because the liver’s interior is relatively soft.
From the capsule, thin sheets of connective tissue extend inward, dividing the liver into its lobules and providing a scaffold that holds everything in place. These internal septa also carry the branches of blood vessels and bile ducts deeper into the organ. The portal triads at the corners of each lobule are surrounded by this fibrous connective tissue. When chronic liver disease causes excess scarring (fibrosis or cirrhosis), it is this connective tissue framework that proliferates abnormally, stiffening the organ and disrupting blood flow through the sinusoids.
Other Cell Types in the Liver
While hepatocytes dominate, several other cell types play important roles. Kupffer cells, the resident immune cells lining the sinusoids, constantly patrol for pathogens and cellular debris entering from the gut. Stellate cells, tucked in the small space between hepatocytes and sinusoid walls, store vitamin A and, when activated by injury, produce the collagen fibers responsible for scar tissue. Cholangiocytes are the epithelial cells lining the bile ducts, forming a single layer of cube-shaped cells that help modify bile composition as it flows through the ductal system.
Together, these non-hepatocyte cells make up roughly 20% of the liver’s total cell population. Their balance matters: when stellate cells become overactive, fibrosis develops. When Kupffer cells are overwhelmed, infections can gain a foothold. The health of the liver depends not just on hepatocytes but on the coordinated function of all these cell types.
Functional Segments Used in Surgery
From the outside, the liver appears divided into two main lobes (right and left), but internally it is organized into eight functionally independent segments. This classification, developed by the French surgeon Claude Couinaud, is based on the branching patterns of the hepatic veins and the portal vein. Each segment has its own independent blood supply and bile drainage, which means a surgeon can remove one or more segments without cutting off blood flow to the rest of the organ. This segmental anatomy is what makes partial liver removal and living-donor transplantation feasible.
How Size Varies by Body Weight
Liver weight scales with body size. According to reference data from the College of American Pathologists, a woman weighing around 150 pounds typically has a liver with a median weight of about 1,500 grams, while a man at the same weight is similar at roughly 1,480 grams. At higher body weights, the liver grows proportionally: a man weighing over 230 pounds has a median liver weight of about 2,390 grams, nearly 5.3 pounds. This scaling reflects the organ’s metabolic workload, since a larger body produces and processes more nutrients, hormones, and waste products that the liver must handle.
An unusually enlarged liver can signal disease. Fat accumulation, inflammation, congestion from heart failure, or tumor growth can all push liver weight well beyond the normal range. Conversely, advanced cirrhosis can cause the liver to shrink as functional tissue is replaced by scar tissue.