What Do Emotional Tears Actually Do?

Tears as a result of emotional states? What do emotional tears actually do? The purpose of tears in lubricating the eyes or in protecting them, washing them in various ways. Why is it that humans have this upwelling of fluid in their eyes that overflows the eyelids and runs down the face when they're feeling joy or surprise or sadness or terror? We'll get more into this question in the second episode than in to day's episode.