|Section2= |Section3= }} Bilirubin (formerly referred to as hematoidin)'s the yellow breakdown product of normal heme catabolism. Heme's found in hemoglobin, a principal component of red blood cells. Bilirubin's excreted in bile, and its levels are elevated in certain diseases. It's responsible for the yellow color of bruises and the yellow discoloration in jaundice. It's also been found in plants. Chemistry Bilirubin consists of an open chain of four pyrrole-like rings (tetrapyrrole). In heme,… (More on Bilirubin)