Bilirubin metabolism conjugated unconjugated

• published: 16 Apr 2015
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Talk to you about this yellow stuff we call bilirubin that is the examiner might ask you question just little bit below the belt, how bilirubin is formed that's usually enough to bring everyone to their knees. So let me remind you there is a red blood cell an erythrocyte born and bred in the bone marrow via a process known as erythropoiesis and red blood cells do not go living for ever they have a life span of 120 days and after that is breaking down and releasing this substance called haemoglobin so the real question is how do we go from haemoglobin a 4 ring arrangement a cyclic tetrapyrrole to bilirubin again a tetrapyrrole but arranged in a linear fashion and the first thing that happens is that the iron of the haemoglobin goes then the globulin part goes leaving this skeleton this ring structure which is the broken at one of these points and opened up and unrolled just like sausage roll and that is enzyme responsible for this unrolling effect called the hem oxygenase enzyme which is found in the reticuloendothelial system that is the spleen and the lymph nodes. So the vast majority of bilirubin comes from break down of red blood cells and is changed from a compound like this by removing the iron and the globulin parts which are then recycled and turned in to this yellow stuff we call bilirubin because this ring is broken at one of these points via the hemoxygenase enzyme and unrolled via the hemoxygenase enzyme dramatic clever but that is how it is. Now that is ordinary bilirubin we must remember something about bilirubin it exist in 2 forms conjugated and unconjugated forms roughly difference between them is that unconjugated bilirubin is toxic and can injure cells in high concentration and kill them particularly that of the brain cells and babies with high level of this compound in the blood have disease called kirnicturis and may very well die so what we do is we make it non toxic water soluble so that it can not penetrate in to cells and it can be excreted. Quick review there are 2.types bilirubin conjugated and unconjugated bilirubin unconjugated bilirubin is toxic and can kill cells so that it is reasonable that haemolytic jaundice where there is lots of unconjugated bilirubin in the blood is never sever and what we do we conjugated it in the liver we join it with another chemical glycogenic acid and make it water soluble and it can be excreted and it leaves the biliary tree to be excreted and the biliary tree at this point consists of little canals called the biliary canaliculi. So that is all we need to know about bilirubin how is is formed something about conjugation if we did not conjugate bilirubin we all be permanently jaundice there is an animal called the gunn rat it can not conjugate bilirubin so want colour is it yes yellow and does it die early yes it does it dies for 2 reasons firstly because of brain disease kirnicturis and secondly people are so interested in following its unique bilirubin metabolism and kill it because is a classical model.