The 2 bile pigments present in stool are Biliverdin and Stercobilin.
The gallbladder contains the digesting fluid called bile, which is generated by the liver. It is essential to the breakdown and absorption of lipids. A pigment known as bilirubin is released during the breakdown of red blood cells and is finally expelled as bile. Bilirubin alters chemically during digestion, resulting in the production of the two primary bile colors that are detectable in stool:
Biliverdin: This green pigment is a product of the breakdown of heme, a component of hemoglobin found in red blood cells. Biliverdin gives a greenish color to bile and can contribute to the coloration of stool.
Stercobilin: This brown pigment is formed from the breakdown of biliverdin. It is the main pigment responsible for the brown color of normal feces. Stercobilin is produced as biliverdin undergoes further metabolism in the intestines.