 sinusoidal capillaries (sinusoids), the vascular channels between the plates of hepatocytes.  perisinusoidal spaces (spaces of Disse), which lie between the sinusoidal endothelium and the hepatocytes.
With this information as background, one can now consider several ways to describe the organization of these structural elements to understand the major functions of the liver.
periportal space (space of Mall) capillary terminal branch of hepatic artery terminal branch of portal vein portal canal
FIGURE 18.2 • Blood supply to the liver: the portal triad. The portal triad is composed of the branches of the hepatic artery, portal vein, and bile duct. Blood from the terminal branches of the hepatic artery and portal vein enters the hepatic sinusoids. The mixture of venous and arterial blood is transported by the sinusoids toward the terminal hepatic venule (central vein). From here, blood drains into the sublobular veins, the tributaries of the hepatic vein. Note the small vessels and capillary network in the perivascular connective tissue surrounding each hepatic triad within the portal canal. Also note the periportal space of Mall, located between the portal canal and the outermost hepatocytes. This space is also filled with a small amount of connective tissue in which lymph drainage begins. From here, blind-ended lymphatic capillaries form larger lymphatic vessels that accompany branches of the hepatic artery.
There are three ways to describe the structure of the liver in terms of a functional unit: the classic lobule, the portal lobule, and the liver acinus. The classic lobule is the traditional way to describe the organization of the liver parenchyma, and it is relatively easy to visualize. It is based on the distribution of the branches of the portal vein and hepatic artery within the organ and the pathway that blood from them follows as it ultimately perfuses the liver cells.
The classic hepatic lobule is a roughly hexagonal mass of tissue.
The classic lobule (Fig. 18.3 and Plate 65, page 656) consists of stacks of anastomosing plates of hepatocytes, one cell thick, separated by the anastomosing system of sinusoids that perfuse the cells with the mixed portal and arterial blood. Each lobule measures about 2.0  0.7 mm. At the center of the lobule is a relatively large venule, the terminal hepatic venule (central vein), into which the sinusoids drain. The plates of cells radiate from the central vein to the periphery of the lobule, as do the sinusoids. At the angles of the hexagon are the portal areas (portal canals), loose stromal connective tissue characterized by the presence of the portal triads. This connective tissue is ultimately continuous with the fibrous capsule of the liver. The portal canal is bordered by the outermost hepatocytes of the
FIGURE 18.3 • Diagram of a classic liver lobule. A classic liver lobule can be schematically diagramed as a six-sided polyhedral prism with portal triads (hepatic artery, portal vein, and bile duct) at each of the corners. The blood vessels of the portal triads send distributing branches along the sides of the lobule, and these branches open into the hepatic sinusoids. The long axis of the lobule is traversed by the terminal hepatic venule (central vein), which receives blood from the hepatic sinusoids. Note that a wedge of the tissue has been removed from the lobule for better visualization of the terminal hepatic venule. Interconnecting sheets or plates of hepatocytes are disposed in a radial pattern from the terminal hepatic venule to the periphery of the lobule.
lobule. At the edges of the portal canal, between the connective tissue stroma and the hepatocytes, is a small space called the periportal space (space of Mall). This space is thought to be one of the sites where lymph originates in the liver.