Introduction — Morphology of the Liver Lobule

The liver plays a unique role as a metabolic center of the body, and also performs other important functions (Table 1). The macroscopic and microscopic structure of the mammalian liver has been recognized relatively early. In 1833, Kiernan proposed that lobes of the pig liver organized around main branches of the portal vein were built up of small polyhedron morphological units of parenchyma, called lobules, with boundaries made of connective tissue (Kiernan 1833). This classical liver lobule is characterized by the presence of a central vein (terminal hepatic vein) located approximately in the middle of the unit, and of areas of connective tissue at its corners, called portal tracts, that contain interlobular branches of hepatic artery and portal vein, biliary ductules, lymphatic vessels and nerves. Portal tracts are bridged by narrow stripes of connective tissue which accompany terminal afferent arterial and venous branches running between the lobules to supply the sinusoids that lead the blood into a central vein draining the lobule. However, in man and rodents, classical lobules cannot be easily recognized because only a sparse amount of connective tissue septa lies between portal tracts.