Metabolism
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Gripping abdominal pain and jaundice
GS
is a 40 year old, slightly overweight, woman. Recently she has suffered episodes
of what she described as "gripping abdominal pain" after meals, and
she had noticed that her faeces were paler than usual, and floated in the lavatory
pan, but her urine was darker than usual.
When she visited her GP he noted that she had a sallow complexion, and the whites of her eyes were yellow.
What might account for her jaundice?
Why do you think her faeces were pale and her urine dark?
Jaundice is due to an abnormally high concentration of bilirubin, one of the bile pigments in the bloodstream.
Macrophages
take up old red blood cells and oxidise the haem of haemoglobin to bilirubin.
Bilirubin is then conjugated with glucuronic acid in the liver, and excreted
in the bile.
(A number of metabolites of drugs and other foreign compounds (xenobiotics), as well as physiological compounds such as steroid hormones, are conjugated with glucuronic acid in the liver and excreted in the bile.)
Conjugated bilirubin is one of the main compounds that colour faeces. If bilirubin is not excreted in the bile, the faeces will be pale coloured. The bilirubin accumulates in the bloodstream, giving the skin and whites of the eyes a yellow colour, and is excreted in the urine, giving it a dark colour.
What are the two main reasons why jaundice may occur?
Jaundice may occur as a result of:
obstruction of the bile duct, so that bile cannot leave the gall bladder
liver disease (e.g. the various types of viral hepatitis, or alcoholic liver
disease)
How might you distinguish between these two causes of jaundice?
In liver disease the liver has a reduced capacity to conjugate bilirubin, so that there will be unconjugated bilirubin in the circulation.
In obstructive jaundice the liver can conjugate bilirubin normally, but there is impairment of its excretion in bile, so that there will be conjugated bilirubin in the circulation.
A
blood test showed that Ms GS had a high concentration of conjugated bilirubin
in her circulation, suggesting obstructive jaundice. She was sent for ultrasound
scan, which revealed the presence of gall stones, as shown on the right.
She then underwent cholecystectomy (surgical removal of the gall bladder); the excised gall bladder and the gall stones are shown below:
Chemical analysis of the gall stones showed that they were composed mainly of cholesterol, with a small amount of phospholipid and some calcium salts.