Central veins in pigs liver (100X)

Central veins in pigs liver. Image copyright: University of Oslo, CC BY-NC-ND 4.0. (Tissue stain: H+E).

The structural unit in the liver is called a liver lobulus. It is a hexagonal prism that is about 2 mm high and 1 mm wide. A lobulus is bounded by interlobular connective tissue. In a pure cross-section, the lobulus is approximately hexagonal. Often the incision strikes at an angle of the liver lobulus, and then one can see other geometric shapes (triangular, square).

A portal triad is also seen. It consists of these five structures:

proper hepatic artery, an arteriole branch of the hepatic artery that supplies oxygen
hepatic portal vein, a venule branch of the portal vein, with blood rich in nutrients but low in oxygen
one or two small bile ductules of cuboidal epithelium, branches of the bile conducting system.
lymphatic vessels
branch of the vagus nerve

The misnomer "portal triad" traditionally has included only the first three structures, and was named before lymphatic vessels were discovered in the structure.

Published May 26th 2014, updated September 26th 2021.