Neonatal Jaundice Metabolism  -  Excretion
Bilirubin metabolism Excretion		Excretion of bilirubin into bile involves the movement of conjugated bilirubin from the ER of the hepatocyte to the canalicular membrane and its translocation across the membrane into canalicular bile. This last step is an ATP-dependent process that is shared by a variety of other organic anions. It results in a biliary bilirubin concentration 100 times that of the hepatocyte. Beyond the newborn period, hepatic excretion of conjugated bilirubin into bile is the rate-limiting step in the overall clearance of bilirubin from plasma. This is apparent in conditions of markedly increased bilirubin production, such as severe or chronic hemolytic disease, where it is not unusual to see moderate elevations of conjugated bilirubin. However, in the newborn, bilirubin excretion is NOT the rate-limiting step in bilirubin clearance because of the more severe neonatal limitations in conjugation. Return to top of page