Bilirubin is removed from the body primarily through bile and stool after undergoing processing in the liver and intestines.
Bilirubin Excretion Process
The removal of bilirubin involves a multi-step process:
- Liver Conjugation: The liver transforms bilirubin into a water-soluble form. This is crucial because unconjugated bilirubin is not easily excreted.
- Bile Excretion via MRP2: Once transformed into a water-soluble pigment, bilirubin is excreted into the bile by the MRP2 carrier protein, located at the canalicular membrane of the hepatocyte. This protein actively transports the conjugated bilirubin into the bile ducts.
- Intestinal Degradation: Bilirubin enters the gastrointestinal tract via bile. Here, intestinal bacteria degrade the bilirubin.
- Stercobilin Formation and Elimination: The degraded bilirubin is then transformed into stercobilin. Stercobilin is then eliminated with the stool, giving stool its characteristic brown color.
| Stage | Location | Process | End Product | Elimination Route |
|---|---|---|---|---|
| Conjugation | Liver | Bilirubin transformed into water-soluble form | Conjugated Bilirubin | Bile |
| Bile Excretion | Liver (Hepatocytes) | MRP2 carrier protein transports bilirubin to bile | Bilirubin in Bile | Intestines |
| Intestinal Degradation | Intestines | Bacteria break down bilirubin | Degraded Bilirubin | N/A |
| Stercobilin Formation | Intestines | Degraded bilirubin converted to stercobilin | Stercobilin | Stool |
