Overview bilirubin2 Overview bilrubin is a yellow-colored byproduct of hemoglobin (heme) metabolism elevated levels of bilirubin causes jaundice, characterized by yellow skin and sclerae in the newborn, short-lived RBCs results in increased production of unconjugated bilirubin as heme breakdown products, decreased conjugation due to immature UDP-glucuronosyltransferase, and increased enterohepatic circulation due to decreased gastrointestinal activity Pathway Steps from bilirubin production to excretion (see above) (1) reticuloendothelial system (RES) macrophages phagocytose sensescent erythrocytes login to view 2 more bullets (2) bloodstream albumin binds bilirubin and complex is carried to liver login to view 1 more bullet (3) liver hepatocytes take up bilirubin hepatic microsomes conjugate bilirubin with glucoronic acid login to view 2 more bullets conjugated bilirubin = direct bilirubin aka water soluble a portion of conjugated bilirubin is excreted in urine remainder is secreted into bile and then into small intestine (4) gastointestinal tract in terminal ileum and colon, bilirubin is deconjugated by bacterial enzymes and metabolized to urobilinogen login to view 5 more bullets