Fig. 1.

Release of bilirubin into blood and transport to the liver. The rapid increase in oxygen after birth stimulates red blood cell production and senescence, resulting in the release of heme from hemoglobin by the reticuloendothelial system. Heme undergoes metabolism by heme oxygenase and biliverdin reductase, resulting in the production of bilirubin, which is released into the blood and bound to serum proteins. After its uptake into the liver, bilirubin undergoes glucuronidation by UGT1A1, located in the endoplasmic reticulum. Bilirubin-glucuronide exits the hepatocyte where it works its way through the biliary canaliculi into the lumen of the intestines.