We have tear ducts to lubricate and protect our eyes from dust and other particles. The ducts are under the upper eyelids and produce a salty liquid(a tear)that gets spread throughout the eye after each blink. Three types of tears are generated by the human eye. Basal tears are very necessary as they keep the eyes well lubricated. Reflex tears flush out the eye when it becomes irritated. And emotional tears flow in response to sadness, distress, or physical pain.
People cry when they are feeling emotions that are beyond words. The emotion being felt can be extreme sadness, happiness, anger, frustration, resentment etc. When people are mildly happy or mildly sad, they don't usually cry. It's not WHICH emotion the person is feeling that causes crying, it's the LEVEL of emotion being felt that causes it. Emotional tears contain more manganese, an element that affects temperament, and more prolactin, a hormone that regulates milk production. Sobbing out manganese and prolactin is thought to relieve tension by balancing the body’s stress levels and eliminating build ups of the chemicals, making the crier feel better.