What is the body trying to accomplish when you’re about to pass out? (Adrenaline rush, lightheadedness, loss of vision)
In: Biology
yeah, the tunnel vision from adrenaline is very different from passing out from light headedness/fainting.
tunnel vision from adrenaline rush is an evolutionary response. in fight or flight you want to focus on what is immediately in front of you, having increased peripheral vision, and increased distance vision isn’t important so your eyes fire what’s called “the near triad”. your pupils dilate to let in more light (you have better vision with light), your lenses accomodate to bring close objects to clear focus, and your eyes converge a bit. all of these things help you see immediately in front of you better, but they can result in a tunnel vision like effect.
passing out can happen for MANY reasons. some of them are quite benign and don’t require serious medical treatment, some of them *could* be a sign of something less trivial going on. the most common cause of fainting is what we call a vasovagal syncope. here the blood pressure drops and as a result the brain is receiving less oxygenated blood. when this happens the brain shifts focus from non essential functions (like standing up and staying awake) to essential processes (like breathing) so you may lose consciousness. also when you pass out you fall down. and your heart is level with 1) your head and 2) your legs. head being level with your heart means your heart doesn’t have to pump blood to your head against gravity. this is good because as your blood pressure drops that becomes more difficult. legs being level with the heart is important because the blood pooled up in you legs (actually a big percentage of your total blood volume) can make its way back to your heart and to your lungs without fighting gravity as well, and if less blood pools in your lower body that means more blood is in your upper body and this can help increase blood pressure (and remember, low pressure is often the reason you fainted in the first place)
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