ABSTRACT
174The liver is a large digestive gland that composed of parenchymal cells and lattice fibers. The fish hepatic parenchyma is not arranged into distinct lobules. Three patterns of organization of fish hepatic parenchyma are recognized. The first pattern is composed of hepatocytes, which are radially arranged around the central vein. The second arrangement called tubular pattern in form of tubules and the sinusoids form network around the tubules. The third arrangement is present in some fresh and marine teleosts, the hepatocytes lie in anastomosing lamina around the central vein. Also, the biliary tract structures are classified into four types: isolated type, biliary-arteriolar tract type, biliary-venous tract type, and portal tract type. The hepatic satellite cells (perisinusoidal cells) are observed in many species. The sinusoids are lined by endothelial and Kupffer cells. The pancreas of fish is a lobulated compound acinar gland, divided into exocrine and endocrine portions. Exocrine pancreatic tissues consist of scattered serous acini, and are observed in two forms: (a) disseminated in the spleen tissue, in mesentery around intestine and intestinal bulb, and (b) intrahepatically, around the branches of the portal vein. Two alveolar cell types are present in pancreatic acini: centroacinar cells and typical pyramidal acinar cells. Pancreatic stellate cells are demonstrated in the perivascular and the periacinar space of the pancreas. The acini show high lipase and alkaline phosphatase activity, and moderate activity for acid phosphatase. The duct system is composed of intralobular duct, interlobular pancreatic duct, and main duct. The endocrine parts of the pancreas are organized as lightly staining Langerhan’s islets between exocrine acinar cells and consisted of three cell types: alpha, beta, and delta cells and in some species additional F cells are present.
