Where is the code that actually changes the password

We have a site that uses WordPress for part of the site and a separate framework for another part of the site. We are trying to integrate the users of the two systems and need to be able to pass information from WordPress to the other system when a user changes his password. What functions should I be looking at for this? I have tried to look through the user-edit.php file to find where the password is changed but have been unable to find that information.

Thanks in advance for any help you are able to provide.