Bilirubin

n. red-yellow pigment in urine and blood and bile

Bilirubin is a yellow breakdown product of normal heme catabolism. Its levels are elevated in certain diseases and it is responsible for the yellow colour of bruises and the brown colour of feces. Bilirubin reduction in the gut leads to a product called urobilinogen, which is excreted in urine.
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Bilirubin /bil·i·ru·bin/ a bile pigment produced by breakdown of heme and reduction of biliverdin; it normally circulates in plasma and is taken up [more]Bilirubin - Community and Resources

Noun
1. an orange-yellow pigment in the bile that forms as a product of hemoglobin; excess amounts in the blood produce the yellow appearance observed in jaundice
(synonym) hematoidin, haematoidin
(hypernym) animal pigment

n. bilirubin, red-yellow pigment in urine and blood and bile