Complex sentence: Urobilin is produced when Urobilinogen is oxidized by intestinal bacteria; it can also be produced when urobilinogen is exposed to the environment upon urination, resulting in its oxidation to urobilin.
Split into simpler sentences: Urobilin is produced when urobilinogen is oxidized by intestinal bacteria. Also, when urobilinogen in urine is exposed to the environment upon urination, it is oxidized to urobilin.