Veterinary Clinical Biochemistry and Laboratory Diagnosis-II

JAUNDICE - CHEMISTRY AND CLASSIFICATION

Chemistry: View image..

• Jaundice is a term used to indicate clinically evident bilirubin excess in blood.
• In healthy subjects, the level of bilirubin in plasma is <15 µmol/L.
• Jaundice clinically evident if plasma bilirubin >150 µmol/L.
• Occurs - imbalance between production and removal of bilirubin i.e. production exceeds the hepatic capacity to excrete it.
• The life span of Red blood cells is 120 days.
• At the end - broken down by the RE (reticuloendothelial) system, mainly in the spleen.
• Finally, the RBC is broken down by the RE (reticuloendothelial) system, mainly in the spleen as follows.

Haemoglobin -------> Haem + Globin (protein)
Haem -------------> Iron + Biliverdin ---------> Bilirubin

• 80% bilirubin comes from haemoglobin; the rest from other haem-proteins viz. myoglobin and cytochromes.

Transport of Bilirubin:

• Bilirubin is not water soluble.
• Therefore, transported to the liver mainly bound to albumin, some bilirubin is free /unbound.
• Free unconjugated bilirubin is lipid soluble.
• This bilirubin will easily pass to the brain where it is toxic, particularly in premature babies and neonates, causing kernicterus.

Breakdown of Bilirubin

• In the liver about 300-500 µml of unconjugated bilirubin/day is transferred.
• In liver cells, bilirubin is bound to cytosolic proteins Viz. ligandin and transported into the smooth endoplasmic reticulum (SER).

• In the SER, bilirubin undergoes conjugation to mono- and di-glucuronides.
• This reaction is catalyzed by the enzyme, uridyl diphosphate (UDP)-glucuronyltransferase.
• Conjugated bilirubin is water soluble and is excreted in the bile.
• Obstruction in the bile duct increases the plasma bilirubin.
• In the gut: The gut bacteria converts the Bilirubin into Urobilinogen (Colourless)
• Some is reabsorbed, re-excreted in bile or excreted in urine. The rest is lost in faeces directly.

Classification of Jaundice

• Pre-Hepatic : Haemolytic Jaundice.
• Hepatic/ Intrahepatic : Hepato-cellular Jaundice.
• Post/ Extra hepatic : Obstructive Jaundice.