This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'Bilirubin is the degradation product of - \nSelect and explain. \nA. Albumin, B. Globulin, C. Heme, D. Transferrin', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Bilirubin metabolism \n\nBilirubin is the end product of heme degradation.\nThe heme is derived from -\n\n\nSenescent erythrocytes by the mononuclear phagocytic system in the spleen, liver and bone marrow (major source).\nTurnover of hemoproteins (e.g. cytochrome p.450).\n\n\nHeme is oxidized to biliverdin by heme oxygenase.\nBiliverdin is then reduced to bilirubin by biliverdin reductase.\nBilirubin is transported to the liver in bound form with albumin.\nThere is the carrier-mediated uptake of bilirubin in the liver.\nThis bilirubin is conjugated with glucuronic acid by UDP glucuronosyl transferase (UGT1A1) to from conjugated bilirubin (bilirubin glucuronides).\nConjugated bilirubin is excreted into bile.\nMost of the conjugated bilirubin is deconjugated and degraded to urobilinogen.\nThe most of the urobilinogen is excreted in the faeces.\nApproximately 20% of the urobilinogen is reabsorbed in the ileum and colon and is returned to the liver, and promptly excreted into bile → Enterohepatic circulation.\nThe small amount that escapes this enterohepatic circulation is excreted in urine.', 'role': 'assistant'}]