Comparative histologic anatomy of vertebrate liver

Introduction: The aim of the study was to compare the histological features of the liver of vertebrates and demonstrate the possible histological evolutionary trend within the sub-phylum vertebrata . Materials and Methods: Liver tissues were dissected from the five vertebrate classes; the Fish (Cat-fish - Clarias gariepinus ), Amphibian (Rana tigrina), Reptilian (Lizard - Agama aculeata ), Avian (Domestic bird- Gallus gallus domesticus ), and Mammalian (Wistar rat- Rattus norvegicus ) were used for the study. The tissue samples were fixed in 10% formal-saline and processed using standard histological techniques. The liver tissues were studied with a light microscope and photomicrographs were obtained. Results: The results showed structural similarities of the liver across the sub-phylum, with noticeable differences in the hepato-sinusoidal arrangements, composition and association of the bile duct and presence of portal triad. The study observed a gradual transition of hepatocytes distributions in singles and clusters to cord-like as observed in Gallus gallus domesticus and Rattus norvegicus . The study also revealed incomplete portal triad in Clarias gariepinus and Rana tigrina . The observed variations were attributed to adaption, feeding mechanism, mode of nutrition and selective specialization, which are important ecological and biological changes involved in evolution. Conclusion: This study has established that evolutionary trends occurred within the subphylum vertebrata.