The vessel through which blood leaves the liver is the hepatic vein. It is readily identified because it travels alone (inset) and is surrounded by an appreciable amount of connective tissue (CT). If more than one profile of a vein is present within this connective tissue, but no arteries or bile ducts are present, the second vessel will also be a hepatic vein. Such is the case in the inset, where a profile of a small hepatic vein is seen just above the larger hepatic vein (HV).
cells appear as cords radiating from the central vein. Such a lobule is outlined by the dashed line in fgure above.
The limits of the lobule are defned, in part, by the portal canal. In other directions, the plates of the lobule do not appear to have a limit; that is they have become contiguous with plates of an adjacent lobule. One can estimate the dimensions of the lobule, however, by approximating a circle with the central vein as its center and incorporating those plates that exhibit a radial arrangement up to the point where a portal canal is present. If the lobule has been cross-sectioned, the radial limit is set by the location of one or more of the portal canals as indicated by the bile ducts (BD) in this fgure.
KEY BD, bile duct CT, connective tissue CV, central vein (terminal hepatic venule) HA, hepatic artery HV, hepatic vein L, lymphatic nodule PV, portal vein asterisks (bottom fgure), blood sinusoids dotted line (top fgure), approximates the limits of a lobule
There are three ways of describing the liver parenchyma in terms of a functional unit, “classic” lobules, portal lobules, or acini. The classic lobule is a roughly hexagonal block of tissue that has at its center the terminal hepatic venule (central vein) and at its six corners the portal canals (portal triads) containing in each a branch of the portal vein, hepatic artery, and bile duct. The portal lobule is a triangular construct that emphasizes the exocrine secretory function. It has as its axis the bile duct of the portal triad of the classic lobule, and its outer margins are imaginary lines drawn between the central veins closest to that portal triad. The liver acinus provides the best correlation among blood perfusion, metabolic activity, and liver pathology. The acinus is a small diamondor lozenge-shaped mass of tissue that has as its short axis the fine branches of the portal triad that lie along the border of two classic lobules and as its long axis a line drawn between the two central veins closest to the short axis. The hepatocytes in each acinus are described as arranged in three concentric elliptical zones around the short axis; zone 1 is closest to, and zone 3 is farthest from, the axis.
Central vein, liver, human, H&E ×500; inset ×800.
The central vein and surrounding hepatocytes from lower figure of Plate 65 are shown here at higher magnification. The cytoplasm of the hepatocytes in this specimen has a foamy appearance because of extraction of glycogen and lipid during tissue preparation. The boundaries between individual hepatocytes are discernable in some locations but not between those cells where the knife has cut across the boundary in an oblique plane. Frequently, when cell boundaries are observed at still higher magnification (inset), a very small circular or oval profile is observed midway along the boundary. These profiles represent the bile canaliculi (BC).
The cells that line the sinusoids (S) show little, if any, cytoplasmic detail in routine preparations. Perisinusoidal macrophages (Kupffer cells [KC]) are generally recognized by their ovoid nuclei and the projection of the cell into the lumen. The endothelial cell, in contrast, is a squamous cell that has a smaller, attenuated or elongated nucleus. Some nuclei of this description are evident in the micrograph.