Re: When we cry how do our tear ducts form tears?

Dear Sarah,

The tear ducts do not fom tears, it is the two lacrimal glands (tear 
glands) that have the responsibility of forming tears. These are relatively 
small glands, each about the size of a lima bean, located above and to the 
right of the right eyeball and above and to the left of the left eyeball, 
although a small portion of each gland continues a little way into the 
substance of each eyelid. These glands have lots of capillaries and as the 
fluid portion of the blood leaves the capillaries it is taken up by the 
cells of the lacrimal gland and they manufacture tear. Small tear ducts 
(about 6 to 12 for each eye) deliver the tear into the space between the 
eyeball and the eyelid.

You may be interested in knowing that tear is a sterile fluid and that it 
contains lots of antibacterial agents manufactured by these cells of the 
lacrimal gland as well as lots of antibodies manufactured by plasma cells. 
These antibodies are taken up by the cells of the lacrimal gland and 
incorporated into tear.

Another interesting point concerning tear is that it is made and released 
continuously. As a matter of fact, every time we blink our eyes, the 
eyelids act as windshield wipers and wipe the tear across the surface of 
the cornea (the shiny part of the eyeball) to keep it moist and protected 
against microorganisms.

The last interesting point I'd like to tell you about is when you cry the 
lacrimal glands go into "over-drive" and produce a lot of fluid. Ususally 
this is in response to a foreign substance coming into contact with the 
cornea (such as onion vapors or an eyelash under your contact lenses) or do 
to emotional distress (such as watching a sad movie).

I hope this helps,

Leslie P. Gartner, Ph.D.
Associate Professor of Anatomy
Dental School 
University of Maryland
Baltimore

lgartner@umaryland.edu