Why do you tear up when you're sad?

Humans have lacrimal, or tear, glands on the underside of their upper eyelids. These organs produce a salty fluid that washes over your eyes every time you blink, keeping them moist and free of irritating particles. Scientists are still trying to figure out why people produce a surplus of tears when we are upset. Crying communicates your feelings of sadness to others. But there may be an additional reason for tears: When you're upset, your body produces high levels of various stress hormones, or chemical messengers that regulate different body functions. Scientists believe that emotional tears may help to flush these chemicals out of the body, relieving the body's stress.

i think your brain produces hormone call Prolactin when you are sad