Jaundice: Chemistry and Classification
JAUNDICE - CHEMISTRY AND CLASSIFICATION
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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
![Ictrus eye Ictrus eye](http://14.139.56.154:82/file.php/183/Topic-4/Ictrus_eye.JPG)
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.
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Last modified: Monday, 4 June 2012, 6:21 AM