The functional unit of the liver is the what?

• A. Hepatic acinus
• B. Portal triad
• C. Liver parenchyma
• D. Hepatic lobule

Answer: (D)

Think of the liver as a repeating unit that coordinates blood flow, metabolism, and bile secretion. This unit is the hepatic lobule, built around a central vein, with six portal triads at its corners. Blood from the portal vein and hepatic artery pass through the sinusoids toward the central vein, allowing hepatocytes to detoxify and process nutrients along the way. Meanwhile, bile produced by hepatocytes is collected into bile canaliculi that drain toward the bile ducts in the portal triads. This organized, hexagonal arrangement—airing the same functional pattern throughout the liver—embodies how the organ performs its tasks, making the lobule the functional unit. Note that the hepatic acinus describes a metabolic subdivision based on oxygen diffusion and activity, which is a finer way to think about liver function, but the lobule is the standard structural functional unit. The portal triad is a structural landmark within the lobule, not the unit itself, and liver parenchyma refers to the tissue that carries out functions rather than the unit of organization.