bile pigment

Bile pigment, also known as bilirubin, is a brownish-yellow substance produced in vertebrates as a byproduct of red blood cell breakdown. It is secreted by the liver into bile and gives feces their characteristic color. Bilirubin is formed in bone marrow and liver cells from the breakdown of hemoglobin.1

Normally, bilirubin circulates in the blood attached to albumin and is then processed in the liver, where it is concentrated and mixed with bile. This concentrated bile is stored in the gallbladder before being released into the small intestine to aid in fat digestion. In the intestine, bacteria convert bilirubin into other compounds, which are then excreted or reabsorbed.12

When bilirubin is not properly processed or excreted, it can accumulate in the blood, leading to jaundice, a yellowing of the skin and eyes. Bilirubin can also form gallstones, particularly pigment stones, which are more common in individuals with conditions causing rapid red blood cell destruction. Biliverdin is a green pigment that is an intermediate in the breakdown of hemoglobin to bilirubin. Bilins, in general, are a series of pigments found in bile, as well as in other organisms and plants, where they can play roles in photosynthesis.13456