Tears are a liquid produced by the body's process of lacrimation to clean and lubricate the eyes. The word lacrimation may also be used in a medical or literary sense to refer to crying.

One lacrimal gland is located above and beside each eye, behind the upper eyelid. The lacrimal glands secrete lacrimal fluid which flows through lacrimal ducts into the space between the eyeball and lids. When the eyes blink the lacrimal fluid is spread across the surface of the eye. The lacrimal fluid flows through the lacrimal lake via the puncta to the lacrimal caniliculi at the inner corner of the eyelids then through the nasolacrimal duct, and finally into the nasal cavity. An excess of tears, as with strong emotion, can thus cause the nose to run.

Types of tears

There are three basic types of tears:

1. Basal tears: In healthy mammalian eyes, the cornea is continually kept wet and nourished by basal tears. They lubricate the eye and help to keep it clear of dust. Tear fluid contains water, mucin, lipids, lysozyme, lactoferrin, lipocalin, immunoglobulins, glucose, urea, sodium, and potassium. Some of the substances in lacrimal fluid fight against bacterial infection as a part of the immune system.
2. Reflex tears: The second type of tears results from irritation to the eye by foreign particles, or substances such as onion vapors or tear gas or pepper spray. These reflex tears attempt to wash out irritants that may have gotten into the eye.
3. Crying or weeping: The third category, also referred to as crying or weeping, is increased lacrimation due to strong emotional stress or pain. This practice is not restricted to negative emotions; many people have been known to cry when extremely happy. In humans, emotional tears can be accompanied by reddening of the face and sobbing — cough-like, convulsive breathing, sometimes involving spasms of the whole upper body. Tears brought about by emotions have a different chemical make up than those for lubrication.

Diseases and disorders