Tears

Tears are commonly associated with crying

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.

Contents

1 Physiology
2 Types of tears
3 Diseases and disorders
4 Societal aspects
5 Spiritual aspects
6 References
7 External links

Physiology

In humans, the tear film coating the eye has three distinct layers:

The mucous layer contains mucin secreted by the conjunctival goblet cells. The inner-most layer of the tear film, it coats the cornea to provide a hydrophobic layer that allows for even distribution of the aqueous layer.
The aqueous layer contains water and other substances such as proteins (e.g. tear lipocalin, lactoferrin and lysozyme[link]) secreted by the glands of Kraus and Wolfring and the lacrimal gland.
The lipid layer contains oils secreted by the Meibomian glands. The outer-most layer of the tear film, it coats the aqueous layer to provide a hydrophobic barrier that retards evaporation.

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. Lacrimal fluid gathers in the lacrimal lake, then flows via the puncta through the lacrimal canaliculi at the inner corner of the eyelids 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:

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, lacritin, immunoglobulins, glucose, urea, sodium, and potassium. Some of the substances in lacrimal fluid fight against bacterial infection as a part of the immune system.
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 come into contact with the eye.
Crying or weeping: The third category, generally referred to as crying or weeping, is increased lacrimation due to strong emotional stress or physical 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.^{[[Citing sources citation needed]]}

Diseases and disorders

"Crocodile tears syndrome" is an uncommon consequence of recovery from Bell's palsy where faulty regeneration of the facial nerve causes sufferers to shed tears while eating [link].

Keratoconjunctivitis sicca, more commonly known as dry eye, is a very common disorder of the tear film. Paradoxically, sufferers can experience watering of the eyes which is in fact a response to irritation caused by the original tear film deficiency.

Societal aspects

Most mammals will produce tears in response to extreme pain or other stimuli, but crying as an emotional reaction is considered by many to be a uniquely human phenomenon, possibly due to humans' advanced self-awareness. Some studies suggest that elephants and gorillas may cry as well.

In nearly all cultures, crying is seen as a specific act associated with tears trickling down the cheeks and accompanied by characteristic sobbing sounds. Emotional triggers are most often anger and grief, but crying can also be triggered by sadness, joy, fear, humor, etc.

In many cultures, crying is associated with babies and children. Some cultures consider crying to be undignified and infantile, casting aspersion on those who cry publicly. In most western cultures, it is more socially acceptable for women to cry in public than men, but this is certainly not true for all human cultures.

An insincere display of grief or dishonest remorse is called crocodile tears, from the ancient anecdote that crocodiles would pretend to weep in order to lure prey [link].

Many religions describe gods or prophets as crying:

According to a hadith, the prophet Muhammad proclaimed: "This (tears) is an expression of the tenderness and compassion, which the Lord hath put into the hearts of His servants. The Lord doth not have compassion on and commiserate with His servants, except such as are tender and full of feeling."
The shortest verse in the Bible (in the King James Version of the Bible and some other English translations) is simply: "Jesus wept."
Jade is sometimes known as "tears of the Buddha".

The Incas referred to silver as the "tears of the moon".

Spiritual aspects

The Gift of Tears in Shin Buddhism: [Tears] of joy and grief cleanse our souls. Christians as well may perceive tears as spiritual gift when they refer to Gospel of Jesus Christ: "Blessed are you that weep now, for you shall laugh" (Luke 6.21), while [Weeping Icons] are a common feature of the Easten Christian Traditions. [Tears] play an important role in the Eastern Christian Mystic Theology.

References

External links

[Nasolacrimal System Anatomy - eMedicine.com]
The Spiritual Context of Tears - [The Gift of Tears]

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