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: Renal damage as reflected by an increase in serum urea and in kidney weight was prevented by Captopril .
### Output Text:
Renal damage as reflected by an increase in serum <span class="chemical">urea</span> and in kidney weight was prevented by <span class="chemical">Captopril</span> . 