In the order Anura, the liver of most anurans was not observed in the hematopoietic tissue structure, but the liver of the genus Bombina and Xenopus was observed in the PSR. Hematopoietic nodules

were observed in the hepatic lobule in most anuran amphibians. Discussion This study is the first to investigate amphibian livers phylogenically. We aimed to identify the interrelation of hepatocytes, sinusoids, and hematopoietic tissue, and make a comparison with phylogenic development. Circulatory capillaries arrangement in the liver All ingested materials are absorbed via the intestines, and reach the liver through the portal vein. Blood flows from the portal veins at the portal triads through the sinusoid and between the hepatic plates to the central vein. The hepatocyte-sinusoidal structure is physiologically important, not only because hepatocytes take up large molecules (e.g., amino acids, glucose, and vitamins) from Salubrinal order the sinusoid, but also because a large number of macromolecules (e.g., lipoproteins and albumin) are secreted

into the sinusoid [1]. In mammalian livers, hepatocytes are closely contacted with sinusoidal capillaries that form a dense network [2]. In teleosts, Veliparib hepatocyte-sinusoidal structures are shown as a rough network [1–3, 13]. This study has shown that the hepatocyte-sinusoidal structures of amphibian livers can be classified into three different types: (I) several-cell-thick plate type, (II) two-cell-thick plate type, and (III) one-cell-thick plate type. This classification is based on the investigation of Elias and Bengelsdorf in several vertebrate Morin Hydrate animals [2]. Previous studies described that some fish had a similar structure to normal humans, while others were modified in a more primitive form [3, 21]. Our study of 46 species showed that the primitive form was a combination of several-cell-thick plate and two-cell-thick plate types in the genus Hynobius. The traditional form was the combined two- and one-cell-thick plate type, and was observed in another genus, the Hynobius group, genus Andrias and the Salamandridae family. The mammalian form was the one-cell-thick plate type,

and was observed in the order Anura, order Gymnophiona and part of the order Caudata. It is well known that the phylogenetic relationships in amphibians is clearly categorized (Table 1). Anura is the sister group of Caudata to the exclusion of Gymnophiona [18]. In this study, we revealed that anuran livers had structures identical to the mammalian arrangement, which possess higher metabolic functions. In contrast, urodeles livers had sinusoids of a primitive form, which were narrow with an undeveloped network, identical to teleosts. As phylogenetic relationships are branched from urodeles to anurans, the parenchyma arrangement progressed from the combined several- or two-cell-thick plate to the one-cell-thick plate type, and the hepatocytes changed from round to square and polyhedral cells.