Tears

Tears are a clear liquid secreted by the lacrimal glands (tear gland) found in the eyes of all land mammals (except for goats and rabbits). Their functions include lubricating the eyes, removing irritants, and aiding the immune system. Tears also occur as a part of the body's natural pain response.

Humans are the only mammals known to produce tears as part of an emotional response, such as out of joy or grief. Emotional tears are also significantly different in chemical composition from those caused by irritation (reflex tears) or those that are continuously present (basal tears).

Tears

Composition

Tears are made of water, electrolytes, proteins, and lipids. The exact composition varies between the different types of tears. For example, emotional tears have been found to contain more protein-based hormones, such as prolactin, adrenocorticotropic hormone, and leucine enkephalin (a natural painkiller), than basal or reflex tears.

Types of tears

There are three types of tears:

• Basal tears are omnipresent in our eyes. These constant tears are what keep our eyes from drying out completely. The human body produces an average of 5 to 10 ounces of basal tears each day. They drain through the nasal cavity, which is why we often have a runny nose when we cry.

• Reflex tears are tears that are produced when the eye comes into contact with an irritant such as smoke, onion vapors, or a strong, gusty wind. These tears can be released in large quantities.

• Emotional tears are tears produced from strong emotional stress, pleasure, anger, suffering, mourning, or physical pain.

Functions

Tears serve several key roles in the body:

• Lubrication: Basal tears serve the purpose of lubricating the eye, keeping it moist and nourished.

• Clearing debris: Both basal tears and reflex tears help clear out debris and keep the eyes comfortable.

• Fighting infection: Tears contain lysozyme, a powerful antimicrobial agent that helps keep the eyes healthy.

See also

• Lacrimal gland
• Lysozyme
• Prolactin
• Adrenocorticotropic hormone
• Leucine enkephalin