I was wondering what triggers the tears when we are sad, frustrated, angry, etc.
If you want to get into actual physical parts of the body that hold emotion, then consider the body's junk drawer - the pelvis. Any emotion or stresses that we don't want to deal with finds it's way into the pelvis (and can cause tightening of the hips and lower back). When we finally open the junk drawer (either by performing specific yoga postures or even having sex), the brain finds the pent up emotions and releases them in the form of tears and crying (this is where @Danielles perfect scientific explanation takes over).
emotional tears are largely under the control of the hypothalamus of the brain. There is also involvement from the trigeminal and facial nerves. Emotional tears also have a different composition than tears that are involved in keeping your eyes lubricated
I would imagine the brain sends like a little message to the tear ducts when you are sad/angry/frustrated and the tear ducts clean themselves by releasing the fluids also known as tears :) thats my best guess (:
hm, waht triggers the tear ducts then?
Tear ducts leak water.