The science of tears

What happens when we cry? Why do we get a stuffed nose from it? Are there different types of tears?

What are tears?

Tears are a solution of salts, proteins, oils and mucus and are released from the lacrimal gland that is positioned in the outer corner of your eye. The proteins that are present in tears include antibodies (part of the immune system to fight infection), lysozyme (an enzyme which can attack bacterial cell-walls) and many other interesting little proteins. “Proteins” are so much more than just your muscles. They have the most bizarre and amazing functions in your body!

Tears drain into the nasal cavity, which explains your stuffy nose after another tragically ending love-story in the lab.

1024px-Tear_system.svg

Eye: Anatomy of lacrimation, showing a) Lacrimal gland b) Superior lacrimal punctum c) Superior lacrimal canal d) Lacrimal sac e) Inferior lacrimal punctum f) Inferior lacrimal canal g) Nasolacrimal canal (image credit: FML’s and User:Erin_Silversmith)

Did you know that there are different types of tears?

There are three types of tears: basal tears, reflex tears and emotional/psychic tears:

Basal tears are needed in your eye as lubricants, meaning that they prevent your eyes from drying out.

Reflex tears are produced when something is irritating your eye (like methanol/formaldehyde mixed with hot steam). This is a neat reaction involving the sensory nerves of your cornea that sends a warning-message to the brain stem (via the ophthalmic nerve). The brain stem cooks up some hormones that are sent to the eye-lid glands, which then produce tears. The tears then hopefully rinse away the irritation. This response is also triggered when you vomit, cut onions, yawn or cough. I for example, have a very sensitive nerve in my left ear. If I poke this ear, I start to cough and this coughing starts the described response and I start “crying”. The body is a weird thing.

Emotional or psychic tears are a result of a trigger of the endocrine system via the hypothalamus (part of the brain) which sends signals to the glands in the eye, and you start sobbing. The trigger can be happiness, pain, sadness, men in the lab and other emotional things. Interestingly, emotional tears have different content compared with reflex tears that contain almost 98 % water.  Emotional/psychic tears instead contain a complex mixture of chemicals such as prolactin (also involved in breast-milk production), adrenocorticotropic hormones (indicators of high stress) and leucine-enkephalin (one of your own in-house happy-painkillers).

1024px-Sépulcre_Arc-en-Barrois_111008_12

Emotional tears? (image credit:  Vassil)

If you cut the trigeminal V1 nerve (a cranial nerve), your reflex-tears will stop flowing, but you are still able to cry due to emotions. Hence, the different groups of tears are indeed different in both origin and function. Also, a new born baby cries without tears due to the nervous system still not being fully developed.

It has been suggested that crying is good for stabilizing the mood and feeling better. Hence, according to science, crying might be a very good thing. It may release the stress before it is taken out on others. 

[Tweet “What happens when we cry? Why do we get a stuffed nose from it? Are there different types of tears?”]

Onions

OK, I just have to mention onions. I love onions, but I am so sensitive to onions that I have actually gotten myself a pair of #distractinglysexy lab glasses to use when I am cutting them. It prevents the volatile tear-generating sulphur-containing compounds from reaching my eyes.

Intact onion cells have no odour since the reacting chemicals are compartmentalized into different parts of the cell and do not come in contact with each other. It is first upon cutting the chemicals come in contact with each other and a chemical reaction starts that produce these tear-bombs. If you rinse the onion in water, it will be a lot easier not to cry.

Science Safely!

Dr. Anna of The Imaginarium

...should really try to cry more.

…should really try to cry more.

Corneal nerves: structure, contents and function. By: Muller, LJ; Marfurt, CF; Kruse, F; et al. EXPERIMENTAL EYE RESEARCH  Volume: 76   Issue: 5   Pages: 521-542   Published: MAY 2003

Gachon, A. M., P. Verrelle, G. Betail, and B. Dastugue. “Immunological and electrophoretic studies of human tear proteins.” Experimental eye research 29, no. 5 (1979): 539-553.

Janssen, P. T., and O. P. Van Bijsterveld. “Origin and biosynthesis of human tear fluid proteins.” Investigative ophthalmology & visual science 24, no. 5 (1983): 623-630.

van Setten, G-B. “Epidermal growth factor in human tear fluid: increased release but decreased concentrations during reflex tearing.” Current eye research 9, no. 1 (1990): 79-83.

Lancaster, Jane E., Martin L. Shaw, and William M. Randle. “Differential hydrolysis of alk (en) yl cysteine sulphoxides by alliinase in onion macerates: flavour implications.” Journal of the Science of Food and Agriculture 78, no. 3 (1998): 367-372.

Posted in Biology, Medicine, The Biology of Disgusting and tagged , , , .

TheImaginarium

Leave a Reply

Your email address will not be published. Required fields are marked *