What is the functional unit of the liver?

• A. The hepatic lobule
• B. The portal triad
• C. The hepatocyte cords
• D. The hepatic acinus

Answer: (A)

The functional unit of the liver is the hepatic lobule. Each lobule is roughly hexagonal and centered on a central vein, with portal triads—containing a hepatic artery branch, a portal vein branch, and a bile duct—at its six corners. Blood from the triads percolates through sinusoids lined by hepatocytes arranged in plates, passes by Kupffer cells, and drains into the central vein. Hepatocytes produce bile that flows into bile canaliculi between cells and is collected by ducts in the portal triads. This organization supports efficient metabolism and detoxification as blood moves from the periportal region toward the central vein, while bile is secreted in the opposite direction toward the bile ducts. The hepatic acinus is another way to describe liver function in terms of zones of metabolism and oxygenation, but the classic histological functional unit is the hepatic lobule.