The chief pigment in human BILE. It is derived from HAEMOGLOBIN which is the red pigment of the red blood corpuscles. The site of manufacture of bilirubin is the RETICULOENDOTHELIAL SYSTEM. When bile is passed into the intestine from the gall-bladder (see LIVER), part of the bilirubin is converted into stercobilin and excreted in the FAECES. The remainder is reabsorbed into the bloodstream, and of this portion the bulk goes back to the liver to be re-excreted into the bile, whilst a small proportion is excreted in the urine as urobilinogen.
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