In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: The homozygous Gunn rats have unconjugated hyperbilirubinemia due to the absence of glucuronyl transferase , leading to marked bilirubin deposition in renal medulla and papilla .
### Output Text:
The homozygous Gunn rats have unconjugated hyperbilirubinemia due to the absence of <span class="chemical">glucuronyl</span> transferase , leading to marked <span class="chemical">bilirubin</span> deposition in renal medulla and papilla . 