Comparative histological study of hepatic architecture in the three orders amphibian livers

The 46 amphibian livers showed a variety of histological features, but anurans were the same as in mammalian livers. The hepatocyte-sinusoidal structures of the amphibian livers were classified into three different types: (I) several-cell-thick plate type, (II) two-cell-thick plate type, and (III) one-cell-thick plate type, depending on the percentage extension of sinusoidal areas per unit area, measured by morphometry. Hematopoietic tissue structures were observed in the connective tissue of both the perihepatic subcapsular regions and portal triads in the order Caudata and Gymnophiona, but were not observed in the order Anura (except for the genus Bombina and Xenopus). As phylogenetic relationships are branched from urodeles to anurans, the parenchyma arrangement progressed from the combined several- and two-cell-thick plate type to one-cell-thick plate type as seen in the mammalian liver type. In contrast, hematopoietic tissue structures were exactly the opposite and did not involve anurans.This study is the first to investigate amphibian livers phylogenically, and their architectural differences are shown in the route of hepatic ontogenesis. In this process, parenchymal arrangement formation is acquired phylogenically. The occurrence of hematopoietic cells may be related with the development of the systemic immune system in the spleen and bone marrow.The liver plays an indispensable part in many processes in the body, particularly those concerned with its metabolism (e.g., protein synthesis, storage metabolites, bile secretion and detoxification) that shoulder a central role into maintaining life, and with certain digestive processes. It is the organ in which nutrients absorbed in the digestive tract are processed and stored for use by other parts of the body.The usual concept of structural and functional unit of the liver is the acinus, containing both the hepatic lobule and portal triad. The hepatic lobule is formed hepatocyte-sinusoidal structures in which co