Bilirubin Metabolism And Jaundice

Question 1

Bilirubin is processed by the liver. Where does this bilirubin come from?

Answer 1

Many produced by macrophages of the retoculoemdothelial system as a production of haem degradation. Some comes from cytochrome and myoglobin breakdown

Question 2

How is bilirubin transported from the reticuloemdothelial system to the liver?

Answer 2

Via the transport protein albumin

Question 3

What enzyme in the liver is responsible for bilirubin conjugation?

Answer 3

UDP-glucuronyl transferase

Question 4

Bilirubin-monoglucuromide and bilirubin-diglucuromide are water soluble. Why is this important?

Answer 4

It allows bilirubin to be excreted across the canalicular membrane of the hepatocyte and into the bile duct

Question 5

Intestinal bacteria convert conjugated bilirubin to urobilinogen. How is urobilinogen excreted?

Answer 5

In urine

Question 6

Some bilirubin is acted upon by intestinal bacteria to produce the compound which gives faeces its characteristic brown colour. What compound is this?

Answer 6

Stercobilinogen

Question 7

What is the normal level of total serum bilirubin?

Answer 7

0.1-1.2 mg/dL

Question 8

At what serum level of bilirubin does jaundice become obvious?

Answer 8

2-2.5mmHg

Question 9

In which structure are the first yellow discolouration signs of jaundice usually seen?

Answer 9

Sclera of the eye

Question 10

What is the major cause of prehepatic jaundice?

Answer 10

Excessive haemolysis of RBCs

Question 11

What signs (bilirubin level, faeces colour etc.) occur with prehepatic jaundice?

Answer 11

Elevated unconjugated bilirubin
Normal colour stool
No bilirubin in urine

Question 12

What signs (bilirubin level, faeces colour etc.) occur with hepatic jaundice?

Answer 12

Elevated unconjugated and conjugated bilirubin
Dark urine
Slightly elevated ALK

Question 13

What signs (bilirubin level, faeces colour etc.) occur with posthepatic jaundice?

Answer 13

Elevated conjugated bilirubin
Dark urine
Pale faeces
Marked ALK elevation
Slight AST/ALT elevation

Question 14

Why is jaundice common in neonates?

Answer 14

Because after birth, newborns must get rid of foetal haemoglobin so there can be excess bilirubin and the hepatic mechanisms for conjugating and excreting bilirubin are not yet fully mature. Breast milk can also act to inhibit conjugation of bilirubin

Question 15

Brain damage is a risk if bilirubin crosses the immature blood brain barrier of a neonate with jaundice. What is this condition called?

Answer 15

Kernicterus

Question 16

How is neonatal jaundice treated?

Answer 16

Phototherapy

Question 17

More serious neonatal jaundice can occur if there is rhesus incompatibility between mother and foetus. T/F?

Answer 17

True

Question 18

What are the common general causes of hepatic jaundice?

Answer 18

Diseases such as cirrhosis and helatitis. Certain drugs. Comditions such as gilberts and primary biliary cholangitis. These all affect the ability of the liver to remove bilirubin from the blood or conjugate it.

Question 19

What are the general causes of post hepatic jaundice?

Answer 19

Blockage of the bile duct beyond the liver which is commonly caused by cholestasis, gallstones and tumours of the bile duct or pancreas

Question 20

Describe the testing method used to find the total and conjugated bilirubin levels.

Answer 20

For conjugated bilirubin a vlood sample is taken and a diazo reagent is added to the serum and a measurement of absorbancd taken and compared to known standards.
To find the total bilirubin, caffeine is added to the serum and this displaces unconjugated bilirubin from albumin. A reagent is added and a measure of absorbance is again taken and compared to known standards

Question 21

A dip test using a test area impregnated with p-dimethylaminobenzaldehyde can help test for…?

Answer 21

Urobilinogen

Question 22

Which molecule on hepatocytes is responsible for the uptake of bilirubin?

Answer 22

Ligandin