When does mac/ubuntu use .bash_profile and/or .bashrc?

Possible Duplicate:
Difference between .bashrc and .bash_profile

Are they both the same type of file in terms of setting the bash terminal settings, and if no .bash_profile exists then it uses .bashrc?

Also, from within my .bash_profile, can I split my configurations into other files and load them from INSIDE my .bash_profile like:

..
source .some_file
soource .some_file2
..

I want to be able to share my .bash_profile file, yet have some private settings kept secret.

I also want to use the same setup for ubuntu and mac, so not sure if things are compatible.