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Thu 3 Jan, 2019 08:07 am
I have two questions:
1- How do some bodily structures have only sympathetic nervous supply? For example, some structures like skin blood vessels have only sympathetic nerves which make these vessels to constrict in fight or flight state. So, in a resting state, how can these vessels be dilated again without parasympathetic nerves?
2- How can epinephrine and norepinephrine work in contrasting ways? For example, in coronary arteries, norepinephrine causes these arteries to constrict through alpha receptors and epinephrine causes them to dilate through beta receptors. In addition, the adrenal medulla's hormones should be used only for fight or flight so a norepinephrine effect shouldn’t exist.
@Mohamed2019,
I have only an elemental knowledge of the human body's response to a fight or flight situation, ( having helped write an essay on "What is the appeal of horror movies?"), so these are just thoughts that might help you answer your questions. The purpose of the constriction of skin blood vessels is to prevent the loss of blood in the event of injury and to make more blood available to the rest of the body. The purpose of constriction of coronary arteries, rather than to restrict blood flow, could be to increase the speed of the flow at the point where the constriction ends, much like the effect of closing off the end of a water hose with your thumb.
@Ponderer,
Thank u very much , you have helped me a lot . But , the first question is still mysterious , I am not asking about the purpose of the VC of skin blood vessels .. Read it again please . On the other hand , the second question is well answered. I thank you again for helping me .
@Mohamed2019,
You're welcome. I thought you probably knew what I wrote about skin blood vessels. I just wrote it in case you didn't. Honestly, I know that you know more about the subject than I do, and I just guessed at the second question. Good guess, I guess. I understand the first question but I can't even guess an answer. But I am glad that I helped you.
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