|MadSci Network: General Biology|
Dear Becky, Thank you for your interesting question or should I say interesting questions, since our eyes are swollen for different reasons after crying and after sleeping. Why do we have swollen eyes after crying is the most interesting question. Tears are salty, watery secretions that keep two important parts of the eye constantly moist. They flow over the cornea, the transparent coating of the eye, and they lubricate the conjunctiva, the membrane covering the white of the eye and lining the inside of the eyelids. Tears also wash away stray bits of dust and grit and help keep your eyes free of infections. These tears that constantly keep your eyes moist, called the basic tear secretions, are produced on the conjunctiva and also in the eyelids. These, of course, do not cause swollen eyes. The tears that we cry over failed exams, lost loves or bitter disputes are reflex tears, generated by the main lacrimal glands in the upper, outer corner of your upper eyelid. When we cry, excess tears overflow down the cheeks while the rest flows through tiny tear drains into the nose and then into the throat. This explains the runny noise and the strange voice that we get when crying. Excessive crying may put strain on the lacrymal apparatus and create redness, or itchiness of the eyes. Rubbing the eyes to relieve this itch also contributes to redness and swelling. This is, however, only half the answer. In fact, the eyes and face become flushed and puffy because of the emotional response that always accompanies crying. To explain this, Iím afraid I have to say a few words about the human nervous system. In addition to our "voluntary" nervous system (which controls actions and thoughts), humans have two "autonomous" nervous systems, which control the parts of the body that work "by themselves", such as the heart or pancreas. The first one, called the parasympathetic nervous system, is controlled by parts of the brain responsible for our day-to-day involuntary bodily functions, such as digestion and breathing. The other, called the sympathetic nervous system, is controlled by centers of the brain and spinal cord that respond to stressful conditions, such as danger or strong emotions. When danger, anger or fear activates the sympathetic nervous system, we experience a "fight or flight" response. Adrenaline surges through our bodies, pupils dilate, the tear glands secrete more fluid, the heart begins pumping more blood more rapidly, breathing quickens, muscles tense, and our senses stand ready to respond to danger. The body reacts to any strong emotion, such as those that cause crying, in this way. The face becomes flushed and puffy from blood flow and from the facial muscular effort that crying generates. Puffy eyes after a nightís sleep is easier to explain. It is most often related to drinking water late at night or having too much sodium in the diet, which causes water retention. Basically, it means that water has accumulated under the skin around the eyes. Such swollen eyes can also be caused by lack of sleep, too much alcohol, salt or caffeine, and there is also a genetic predisposition. As you will see on the internet if you type in "puffy eyes", many remedies are readily available. I hope that this answers your question, Cheers ! Benoit
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