What setup file does eshell (elisp shell) read when it starts? How eshell sets its PATH?

With emacs/eshell, the "echo $PATH" shows different paths than that of $PATH environment variable.

And I also checked that eshell doesn't read .bashrc or .profile, and I think that's the reason why the path is different.

What setup file does eshell read when it starts?
How eshell sets its PATH?
How to make the eshell's PATH the same as the environment variable's PATH?

ADDED

As Jérôme Radix pointed out, the PATH depends on how I start the Aquamcs.

When I click the button to start Aquamacs, it has different PATH.
When I run 'aquamacs' from the command line, it has the same PATH.

Solution

What setup file does eshell read when it starts?

No setup file is executed at startup. The following files are read to define the initial history and last directories :

~/.eshell/history
~/.eshell/lastdir

How eshell sets its PATH?

In esh-util.el, line 240 :

(defvar eshell-path-env (getenv "PATH")
  "Content of $PATH.
It might be different from \(getenv \"PATH\"\), when
`default-directory' points to a remote host.")

How to make the eshell's PATH the same as the environment variable's PATH?

It is the same as the PATH variable of the emacs process. I imagine that you do a echo $PATH on a shell outside emacs to compare. If PATH are differents between emacs and your shell outside emacs it is because emacs and your shell does not execute the same startup scripts.