Nomenclature
Urobilinogen (aka d-urobilinogen) is closely related to two other compounds: mesobilirubinogen (aka i-urobilinogen) and stercobilinogen (aka i-stercobilinogen). Specifically, urobilinogen can be reduced to form mesobilirubinogen, and mesobilirubinogen can be further reduced to form stercobilinogen. Confusingly, however, all three of these compounds are frequently collectively referred to as "urobilinogens".
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