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Tears are the secretions of the lacrimal
glands. These secretions clean and lubricate the eyes. They continually bathe
the cornea, the tough outer layer of the eyeball. Tears protect the eyes from
dirt and infection. They help eyes to wash away foreign particles, such as dust
and hairs and keep them from drying out, which would result in blindness.
Two lacrimal glands, one over each eye, lie
behind the eyelid.They pour out the fluid through several small ducts in the
underside of the eyelid. Every time a person blinks an eyelid, it sucks a
little fluid from the glands. During normal flow, tears wash over the eye and
drain through ducts into the nasal cavity. During heavy flow, the extra tears
spill over the eyelids to wash away particles too large for the ducts.
Strong emotions such as sorrow or elation,
awe, pleasure, irritation of the eyes, laughing, and yawning may lead to an
increased production of tears, or crying.
When a person feels some emotion very strongly, such as a grief or anger, the
muscles around eyes tighten up and squeeze out the tear fluid.
In humans, the tear film coating the eye,
known as the precorneal film, has three distinct layers, from the most outer
surface:
1. Lipid Layer containing oils, coats
the aqueous layer; provides a hydrophobic barrier that envelops tears and
prevents their spilling onto the check.
2. Aqueous
layer containing water and other
substances such as proteins, promotes spreading of the tear film, control of
infectious agents and osmotic regulation.
3. Mucous
layer containing mucin, coats the
cornea, provides a hydrophobic layer, allows for even distribution of the tear
film and covers the cornes.
Types of Tears :
There are three basic types of tears, all
having different purposes.
1.Basal Tears: Basal tears are omnipresent in
our eyes. The cornea is continually kept wet and nourished by basal tears. They
lubricate the eyes, and help to keep them clear of dust. Some of the substance
in lacrimal fluid (such as lysozyme) fight against bacterial infection as a
part of the immune system.
2. Reflex Tears: The second type of tears results
from irritation of the eye by foreign particles, or from the presence of
irritant substances such as onion vapors, smoke or pepper in the eye's environment.
It can also occur with bright light and hot or peppery stimuli to the tongue
and mouth. It is also linked with vomiting, coughing, and yawning. These reflex
tears attempt to wash out irritants that may have come into contact with the eye.
To accomplish this feat, the sensory nerves, in cornea communicate this
irritation to our brain stem, which in turn sends hormone to the glands in the eyelids.
These hormone cause the eyes to produce extra tears.
3. Emotional Tears (Crying Tears): The third
catergory, in general, referred to as crying or weeping, is increased
lacrimation due to strong emotional stress, anger, suffering, mouring, or
physical pain. Process starts in the cerebrum where sadness is registered. The
endocrine system is then triggered to release hormones which then causes tears
to form.
Tears brought about by emotions have a
different chemical make-up than those for lubrication.Emotional tears contain
more of those chemicals which are associated with stress.When these chemicals
are shed along with the tears, we feel relieved as our stress levels come
down.Our body achieves a chemical/emotional balance by releasing extra
chemicals.
Words by Rishi Mangal
[Note: This article was originally published
in Knowledge Quest/July 2012]
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