Both animals and humans can produce tear but the reason for tears can be different in both of them. Tear ducts are present below the upper eyelid which lubricates and protect our eyes from the dust particles. Human eyes produce three types of tears i.e. basal, reflex and emotional.
These are the primary tear which are released regularly and keeps the surface of eyes clean and lubricated. It forms the thin film with every blink to protect the eye.
When some dust particle or micro organisms enters our eye then it responds by producing reflex tears. These tears have different chemical composition from the basal tears. That is why it makes the dust particles to leave the eyes more quickly than the basal tears. While cutting onion, suffering and seasonal allergies our eyes brim with tears and produces reflex tears to get rid of the sufferings. Amino acids sulfoxides are present in onion which is a kind of organic molecule. After cutting the onion skin, allinases (a type of enzymes) forms a mixture with sulfoxides to get sulphenic acid. When it comes in contact with the oxygen the sulfenic acid forms syn-propanethial-s-oxide and thiosulfinates which irritates our eyes and finally the eyes produce reflex tears.
Emotional tears are produced when a person is in the extreme grip of a particular emotion like sadness, anger or sometimes happiness too. Our eyes also produce emotional tears when we are physically injured because our body cannot differentiate between physical and emotional pain.
Emotional tears contain more manganese which highly affects our temperament and also have the enough prolactin, a hormone which is responsible for the regulation of milk production in the body. So when eyes release manganese and prolactin through eyes which drop down the stress and tension level by which the person feels better than before.
Prolactin level is more in women as compared to men which is used while nursing infants and feeding. At that time women feel calmer, sleepy and relaxed because of the release of prolactin.
Beside all this emotional tears are one of the sources of communication. This is the only way for the babies to communicate and inform their parents that they are feeling pain or something is disturbing them. While in adults crying creates a bond with the other person. Crying is a definite proof for the others that the person is in the extreme of a particular emotion for e.g. during funeral crying shows the extremity of sadness. Sometimes people cry because of extreme happiness or getting the unexpected thing which he wants desperately. Most of the people cry after watching an emotional movie which doesn’t mean that yor are total after all but it shows that the person is normal and have feelings. Some researchers say that the people who cry more frequently enjoy good health.
It has not been proved yet that do animals also shed tears because of emotional reasons but it is proved by the scientists in the case of humans and they cannot control the tears when they are in the extreme of a particular emotion.
Women can cry more frequently than the men not only because of higher prolactin level but also their crying is more acceptable than the men in the society.