Bile is yellow due to the presence of bilirubin, a yellow pigment. While bile itself is a greenish-yellow fluid, bilirubin is the primary contributor to its yellow color. Bilirubin is a breakdown product of heme, a component of red blood cells. When red blood cells die, they are broken down, and heme is converted into bilirubin. Bilirubin is then transported to the liver, where it is conjugated and secreted into bile. The conjugated bilirubin is then excreted in the feces, giving feces its characteristic brown color.
Bile plays a vital role in the digestion of fats, helping to break them down into smaller molecules that can be absorbed by the body. While most people associate bile with its yellowish color, it can also appear greenish due to the presence of another pigment called biliverdin. Biliverdin is a green pigment that is formed from the breakdown of heme and is also present in bile.
The presence of both bilirubin and biliverdin in bile is what gives it its characteristic greenish-yellow color. The relative amounts of each pigment can vary, leading to bile that can appear more yellow or more green. However, the primary reason bile is yellow is due to the presence of bilirubin.
