Chemical evaluation of the functions of the liver.

The liver of a healthy adult weights 1650 Gm. on the average and it is by far the largest gland in the body. It consists of lobes which vary in size and differ to some extent in the sources of their afferent blood supplies. The liver is encased in a membrane of connective tissue. This extends into the liver at the transverse fissure of the undersurface (porta) in the form of a tree with innumerable branches. This framework of connective tissue supports the parenchymal cells, blood vessels, and bile ducts. The portal vein, hepatic artery, hepatic vein, and bile ducts enter the liver through the porta also, and undergo equally extensive branching. In its finer structure the liver consists of lobules 1-2 mm. in diameter. The lobules consist of numerous tubular secretory units, each formed by parenchymal cells surrounding a bile canaliculus. The recent investigations of Elias (1949, 1953) have clarified structural relationships of the hepatic lobule to the vascular and biliary systems. Elias finds that the normal adult liver consists of many plates of epithelial liver cells one cell in thickness. The thickness of the plates may increase to 2 or more cells during regeneration of the liver. In lower animals also thicker plates are observed. The plates meet at varying angles to form a labyrinth of communicating cavities of irregular shape. Elias and Sokol (1953) state that the arrangement of the plates depends upon blood pressure and flow within the lobules.