Final answer:
Urobilinogen is oxidized by intestinal bacteria into urobilin, which is excreted in urine, giving it a yellow color.
Step-by-step explanation:
Urobilinogen is oxidized by intestinal bacteria into urobilin. In the process of excreting bile pigments, the liver secretes bilirubin into the bile, which is then transported to the intestine. Here, the majority of bilirubin is converted into stercobilinogen, which eventually forms stercobilin, giving feces its brown color. However, a small percentage of urobilinogen is reabsorbed and converted into urobilin, which is then excreted in the urine and is responsible for its yellow color.
In terms of the process, bilirubin, formed from the breakdown of heme, binds to albumin in the blood and is transported to the liver. In the liver, bilirubin is conjugated with glucuronic acid to become water-soluble before being excreted into the intestine. Intestinal bacteria play a key role in the further transformation of bilirubin, leading to the creation of urobilinogen and eventually urobilin.