Biochemistry - The Science Behind Crying

Crying

A Topic We are All Quite Familiar with After Taking Honors Chemistry

Those of you who know me well will understand just how fitting this topic is for me because I tend to cry... like a lot. I can rarely ever control my emotions, whether they be anxiety, sadness, happiness, or frustration, and I often end up in tears. But emotions aren't the only thing that cause tears. In fact, there are three different kinds of tears; basal tears, reflex tears, and emotional tears. The circumstance and mechanism surrounding each tear determines the chemical makeup which can tell a lot about its biological function. You probably don't know it, but your body is constantly producing basal tears. And by constantly I mean 1.2 ml of tears a day. Basal tears consist of three layers and their main objective is to keep dirt and debris away from your eyes. The first layer, the mucus layer, keeps the whole thing fastened to the eye. The second layer, the aqueous layer, keeps the eye hydrated, repels invasive bacteria, and protects the cornea from damage. The third layer, the lipid layer, is an oily outer film that keeps the surface smooth for the eye to see through and also keeps the other layers from evaporating. The lacrimal glands make basal tears constantly, which contain water, mucin, lipids, lysozyme, lactoferrin, lipocalin, lacitin, immunoglobulins, glucose, urea, sodium, and potassium. The lacrimal puncta drains the old tears away through a complex tube system.

Reflex tears are the kind that collect in your eyes when something is irritating them. These tears contain a high concentration of antibodies to stop microorganisms from damaging your eyes. When a foreign substance is detected by the sensory nerves in your cornea, they communicate this irritation to your brian stem, which then sends hormones to the glands in the eyelids. These hormones cause the eyes to produce tears. Some examples of substances that would trigger reflex tears are tear gas, pepper spray, or onion vapors. When an onion is cut a chemical reaction happens to convert sulfoxides into sulfenic acid, which then becomes Syn-propanediol A-oxide (RS(O)CH₂CH₂R → RSOH + CH₂=CHR). The gas stings the eye and reflex tears kick in to wash away harmful substances.

To your body, strong emotions such as stress, frustration, sadness and happiness feel like a loss of control which can be dangerous. First emotions are registered in the temporal lobe of the cerebrum. Then the endocrine system is triggered to release hormones to the ocular area, which causes tears to form. Emotional tears are sent in to stabilize the mood as quickly as possible, much like an increased heart rate and slow breathing. Emotional tears are produced in such large quantity that they overflow and overwhelm the nasal canal of the tear ducts and flow down our cheeks. Humans are the only species that cry emotional tears and the purpose of these tears is still being determined. Some theories suggest emotional tears work as a social mechanism to elicit sympathy or show submission. While reflex tears are 98% water, emotional tears contain high levels of stress hormones, such as prolactin, Adrenocorticotropic hormones (which indicate high-stress levels), and enkephalin (an endorphin that reduces pain). It seems as if the body is getting rid of these chemicals through tears. This suggests emotional tears directly calm down emotions as well as signal emotional state to others, which makes for easier communication.