2. PHYSIOLOGY
JAUNDICE
The
bile pigment bilirubin
is formed from
haemoglobin and
myoglobin breakdown when the red blood
cells are destroyed by the
reticuloendothelial system Fig. Above.
*
The iron and globin are separated
*
The haem ring
is transformed into biliverdin
and this is
reduced to bilirubin which is yellow
*
Bilirubin combines with albumin and is transported
to the
hepatic parenchymal cell
*
This complex gives the indirect van den Berg diazo reaction
*
In the hepatic parenchymal cell,
the albumin is removed and
the bilirubin is conjugated with glucuronic acid to form a
diglucuronide which is water soluble and is excreted into the
bile canaliculi
*
This substance gives
an immediate diazo reaction
(direct
reaction)
*
The conjugated bilirubin is
excreted via the bile ducts into
the intestine.
*
It is acted upon by intestinal
bacteria converting it into a
colourless urobilinogen and the coloured urobilin
*
Fecal excretion is on an average of 100 to 200 mg.
*
Some of the urobilinogen is reabsorbed and returns
to the
liver to be excreted in the urine.
*
Normally there is less than 1.2
mg of indirect-reacting and
0.3 mg. of direct reacting bilirubin per 100 ml. of serum.
*
Jaundice is apparent when the
serum bilirubin level exceeds
2mg/100 ml.
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