Bilirubin's primary role in the liver is to be processed and prepared for excretion from the body.
The liver plays a crucial role in bilirubin metabolism, taking it from a toxic, unconjugated form to a water-soluble, conjugated form that can be safely eliminated. Here's a breakdown:
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Uptake: The liver cells (hepatocytes) take up unconjugated bilirubin from the blood.
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Conjugation: Inside the liver, the unconjugated bilirubin is conjugated with glucuronic acid, making it water-soluble. This process is catalyzed by the enzyme UDP-glucuronosyltransferase (UGT). This is the key function of the liver in terms of bilirubin.
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Excretion: The conjugated bilirubin is then excreted into the bile, which is produced by the liver and stored in the gallbladder.
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Elimination: The bile travels through the bile ducts to the small intestine. In the intestine, some of the conjugated bilirubin is converted back to unconjugated bilirubin by bacteria. Some of this unconjugated bilirubin is then reabsorbed into the bloodstream (enterohepatic circulation), and the cycle repeats. The remaining bilirubin is further processed by bacteria into urobilinogen and stercobilin, which are excreted in the urine and feces, respectively, giving them their characteristic colors.
Problems with Bilirubin Processing in the Liver:
When the liver is damaged or not functioning correctly, it can't process bilirubin efficiently. This leads to a buildup of bilirubin in the blood, causing jaundice (yellowing of the skin and eyes). Conditions that can cause bilirubin buildup include:
- Liver diseases: Hepatitis, cirrhosis, and liver cancer can impair the liver's ability to conjugate and excrete bilirubin.
- Bile duct obstruction: Blockage of the bile ducts prevents the excretion of conjugated bilirubin.
- Genetic disorders: Some genetic conditions, such as Gilbert's syndrome and Crigler-Najjar syndrome, affect the liver's ability to conjugate bilirubin.
In summary, the liver is essential for converting unconjugated bilirubin into a form that can be safely eliminated from the body, and it plays a central role in bilirubin excretion. Proper liver function is vital for maintaining normal bilirubin levels and preventing jaundice.
