Tell Me Why People Cry!!

I was thinking lately- why do we cry? why do we cry when we are sad? Does it only happen when we get badly hurt? why does some cry when they are happy?
I mean, while laughing we are only taking out energy, but while crying- we are losing lot of water and minerals, so why? Are we losing stress by crying? Is there something in the tears that while losing it, it helps us feel better? How does it help? Is that only an ancient wont that meant to show others we are not feeling well? or well, exciting or something? that we are over normal?

Is it easier for the body to reduce stress by losing water and minerals so it will be diverted by the need of some material, so we will have something to do (fill the supply again) instead of thinking about the ungood?

Is it good to cry when we are overwhelming?
- - WHY CRY?

There is an obvious *purging* of stress with healthy crying (as opposed to dysfunction depression) is it merely a surrogate content?

Do other species cry?

Some species will cry in response to physical pain (horses I vaguely remember) but is this equating physical and emotional pain valid?

Why the association of tear function for eyes and the expression of distress in our species?

Tears have a very normal function with respect to maintaining our eyes and vision but this association with the psychology of stress is not *obvious* and would be interesting to develop further as it is so universal a phenomenon.

Extreme joy and sorrow can both be physically a lot alike in terms of actual *stress* to the system.

For example I really don't get hurt of words (definitely not cry from it), and I don't cry from physical pain usually, and I also am not crying from happiness, and well, mentally- I think I am pretty strong too... but what does bring tears to my eyes?