Zsh not recognizing file changes with search path

Zsh not recognizing file changes with search path

I'm using ZShell with Oh-My-Zsh on OS X 10.8. Updates within my search
path aren't immediately recognized. My search path:
[~]$ echo $PATH
/opt/local/bin:/opt/local/sbin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin
I had git in /usr/bin. I used macports to install git, so after the port
install the new executable is in /opt/local/bin. But git command and which
git still use the older one in /usr/bin. If I open a new terminal window
the new git in /opt is correctly used.
So how do you get zsh to recognize the updates to files in the path during
the current shell session? Is it running some other command that's cached
and needs updating?