Final answer:
Bilirubin is a brown pigment produced by the liver during the breakdown of red blood cells. It can be fractionated into different forms, including direct bilirubin, which is water-soluble and directly excreted in bile.
Step-by-step explanation:
Bilirubin is a brown pigment produced by the liver during the breakdown of red blood cells. It is excreted in the bile and eventually eliminated in feces. Bilirubin can be fractionated into different forms, including total bilirubin, direct bilirubin, and indirect bilirubin. Direct bilirubin, also known as conjugated bilirubin, is water-soluble and directly excreted in bile. It plays a role in the diagnosis of liver diseases and jaundice.