It is a small division of the liver defined at the microscopic level.
It should not be confused with the anatomical lobes of the liver (caudate lobe, square lobe, left lobe, and right lobe) or with any of the functional lobe classification systems.
The two-dimensional microarchitecture of the liver can be viewed from multiple different perspectives:
Shape: hexagonal; divided into centrilobular concentric, midzonal, periportal.
Shape: triangular; centered on a portal triad.
Model: biliary secretion.
Shape: elliptical or diamond-shaped; divided into zone I (periportal), zone II (transition zone) and zone III (pericentral).
Model: blood and metabolic flow.
The term “hepatic lobe”, without qualification, typically refers to the classical lobe.
The liver lobe can be described in terms of metabolic “zones”, which describe the hepatic acinus (acinus terminal).
Each zone is centered on the line connecting two portal triads and extends outward to the two adjacent central veins.
The periportal zone I is the closest to the vascular supply that enters and receives the most oxygenated blood, so it is less sensitive to ischemic injury and makes it highly susceptible to viral hepatitis.
In contrast, centrilobular zone III has the poorest oxygenation and will be the most affected during a time of ischemia.
The zones differ depending on the function:
- Zone I hepatocytes are specialized for oxidative liver functions such as gluconeogenesis, fatty acid β-oxidation, and cholesterol synthesis.
- Zone III cells are most important for glycolysis, lipogenesis, and drug detoxification.
Bridging fibrosis, a type of fibrosis seen in various types of liver damage, describes fibrosis from the central vein to the portal triad.