Question

In post-hepatic (obstructive) jaundice, the concentration of conjugated bilirubin in the blood is higher than that of unconjugated bilirubin because

• A. There is an increased rate of destruction of red blood cells.
• B. The unconjugated bilirubin is trapped by a bile stone produced in the bile duct.
• C. The conjugation process of bilirubin in the liver remains operative without any interference.
• D. The UDP-glucuronosyl-transferase activity is increased manifold in obstructive jaundice.

Hint:

In obstructive jaundice the block is after conjugation, so the liver keeps conjugating bilirubin normally, and it backs up into blood.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
Post-hepatic jaundice, also called obstructive jaundice, happens when bile flow out of the liver is blocked, for example by a gallstone or a tumor pressing on the bile duct. We need to explain why the blood bilirubin in this state is mostly conjugated, not unconjugated.

Step 2: Key Concept:
Bilirubin handling by the liver has three steps: uptake of unconjugated bilirubin into the hepatocyte, conjugation with glucuronic acid by the enzyme UDP-glucuronosyl-transferase (UGT), and excretion of conjugated bilirubin into the bile canaliculi. In obstructive jaundice, the block sits after the liver cell, in the bile duct itself.

Step 3: Detailed Explanation:
Since the hepatocyte itself is not damaged, uptake and conjugation continue as normal, so bilirubin is still turned into the conjugated form at a normal rate.
The block is downstream of conjugation, in the duct system, so the conjugated bilirubin cannot pass into the gut. It backs up and leaks into the blood instead. This is why conjugated bilirubin rises in the blood.
Option 1 is wrong because obstructive jaundice is not caused by more red cell breakdown, that pattern fits hemolytic (pre-hepatic) jaundice, where unconjugated bilirubin rises instead.
Option 2 is wrong because it is conjugated bilirubin, not unconjugated bilirubin, that gets trapped behind a gallstone in the duct.
Option 4 is wrong because UGT activity is not increased in obstructive jaundice, the conjugation step works at its normal rate, it is the outflow that is blocked.

Step 4: Final Answer:
The conjugation step keeps working normally while the exit route is blocked, so conjugated bilirubin builds up in blood. This matches option (C).