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BILIRUBIN METABOLISM#anatomyandphysiology#bscnursing



Bile, which is formed in the liver, has many constituents, including bile salts, phospholipids, cholesterol, bicarbonate, water, and bilirubin. Bilirubin metabolism begins with the break-down of red blood cells (RBCs) in the reticuloendothelial sys-tem. Hemoglobin is released from RBCs and broken down to heme and globin molecules. Heme is then catabolized
to form biliverdin, which is transformed into bilirubin. This form of bilirubin is called unconjugated (indirect) bilirubin. In the
liver, indirect bilirubin is conjugated with a glucuronide, resulting in conjugated (direct) bilirubin. The conjugated bilirubin is
then excreted from the liver cells and into the intrahepatic canaliculi, which eventually lead to the hepatic ducts, the common
bile duct, and the bowel.
Jaundice is the discoloration of body tissues caused by
abnormally high blood levels of bilirubin. This yellow discoloration is recognized when the total serum bilirubin exceeds
2.5 mg/dL.
Physiologic jaundice of the newborn occurs if the newborn’s liver is immature and does not have enough conjugating
enzymes. This results in a high circulating blood level of unconjugated bilirubin, which can pass through the blood-brain bar-
rier and be deposited in the brain cells of the newborn. This can
cause encephalopathy (kernicterus).