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: Hepatocyte tight junctions ( TJs ) , the only intercellular barrier between the sinusoidal and the canalicular spaces , play a key role in bile formation .
### Output Text:
Hepatocyte tight junctions ( TJs ) , the only intercellular barrier between the sinusoidal and the canalicular spaces , play a key role in bile formation . 