A yellow discolouration of the skin, sclera and mucous membrane due to an increase in the serum bilirubin level. This becomes clinically evident when serum bilirubin reaches about 80-100 mol/l.
Physiological jaundice usually
Peaks 48-72 hours
Disappears by 1 week
Does not present before 24 hours
Aetiology of Physiological Jaundice
Hb in neonate =18-19g/dl and in adult =11-14g/dl
Breakdown of excess RBCs (Haemoglobin is a constituent of RBC)
Hb broken into:
Globin - a protein that is conserved and utilised
Haem - cannot be used
degraded and excreted
Bilirubin is a product of this degradation.It causes yellow staining of the tissues.The bilirubin first formed is UNCONJUGATED and FAT SOLUBLE.
It cannot be excreted in bile or urine
- travels in plasma, bound to albumin.
- enters the liver cells with the aid of Y & Z carrier proteins
- becomes conjugated with glucoronic acid
The reaction is catalysed by an enzyme Glucuronyl Transferase
Conjugated Bilirubin is water soluble
It is excreted through the biliary tree into the gut.
Conjugated bilirubin is further catabolised by intestinal flora into:
It forms a major component of bile in faeces. (This gives the characteristic orange colour to faeces.)
A small amount is passed in the urine
Conjugated Bilirubin is unstable
Due to :
The relatively alkaline environment of the duodenum and jejunum
Specific enzymes eg beta glucuronidase Converts back into unconjugated bilirubin.