Electron microscope observations on the intrahepatocytic bile canalicules and sequent bile ductules in the crucian, Carassius carassius.

In the hepatic parenchyme of the crucian, Carassius carassius no interhepatocytic bile canaliculi are detected, but each hepatocyte possesses a single intracellular bile canalicule filled with microvilli protruded from the hepatocyte. The intrahepatocytic bile canalicule originates at the neighborhood of the nucleus to extend to the cell surface where it empties into the intraparenchymal biliary passage running in the interhepatocytic space. The pericanalicular cytoplasm contains many small vacuoles which have possible been elaborated in Golgi complexes and may be discharged by emiocytotic mechanism into the canaliculus, suggesting bile secretion in the crucian liver. The intercellular biliary passage consists of the terminal bile ductule composed of two elongated flat epithelial cells enclosing a narrow and twisted lumen in between; the secondary or middle-sized ductule is surrounded by three cuboidal epithelial cells, and the large bile duct by five or more cuboidal cells and a smooth muscle layer. The basal lamina is detected only in the middle-sized ductule and in the large duct. The intracellular bile canalicules attached to the proximal bile ductule by means of the junctional complex are classified into the "terminal" and "side bile canalicules"; they are attached to the proximal end and the lateral wall of the terminal bile ductule, respectively. The ectoplasmic layer bordering the intracellular bile canalicule is rich in microfilaments which partially enter microvilli, and the epithelial cells of the intercellular biliary duct system are also characterized by abundance of microfilaments. These probably contractile cytoplasmic filaments may control or accelerate bile flow through intrahepatic biliary passages. The periductular or periductal cells closely apposed to intercellular bile passages are thought to be mesenchymal cells such as fibroblasts among which histiocytoid elements are intermingled.