Every once in a while it occurs to me to wonder, why when we feel sad, is it important to our bodies to cry? That is, what physiological good do tears do? How come our bodies make tears in response to sorrow, instead of something else, like tingling hands or sneezing or something like that? I wasn't sure I'd find an answer to this, but then today, lo and behold, I spotted a book called Crying: A Natural and Cultural History of Tears, by Tom Lutz. In it is a chapter on the biology of tears. Reading it, I am amazed and thrilled by what I'm learning.
Crying: A Natural and Cultural History of Tears
by Tom Lutz
- Tears are made up of three major parts: water, various oils to keep them from evaporating too quickly, and a layer of mucin, essentially a lubricant. They also contain hormones and proteins.
- There are also three kinds of tears, each for its own function. The kinds of tears don't just appear given different circumstances, they are also different from each other chemically. The three types are:
- Basal tears - this is the moisture present in your eyes all the time. These tears keep everything lubricated, and, since the surface of the eye is actually irregular and wrinkled and even pocked in places, they help smooth out the surface and make it possible for us to see without distortion.
- Reflex tears - these are the tears your eyes make in response to some physical stimulus, such as smoke in your eyes, or fresh-cut onions, or pepper.
- Emotional tears - these are produced in response to strong emotion, like sadness or fear or even sweet joy.
- Surrounding the eye are all types of glands that are involved in the production of the three types of tears. The largest gland, the lacrimal gland, is just above the eye and below the brow bone. This one goes to work big-time when your eye wants to make reflex or emotional tears.
- In the pink part in the corner of your eye is a little duct called the puncta. It is through this duct that the basal tears drain regularly. The puncta can only handle a little bit of moisture at a time. This is why we're not all walking around with tears streaming down our faces on a regular basis. But when we cry, or when we get our eye poked pretty good, the glands make way more moisture than the puncta can handle, and the tears overflow and spill out of the eye. This is why, when somebody starts crying, you see the tears "well up" as people like to say, but then if the person is able to check the emotion, the tears seem to disappear. Really, they just drain out through the puncta.
Tom Lutz, Crying: A Natural and Cultural History of Tears, W.W. Norton & Company, 1999