No Parasympathetic Innervation in Blood Vessels?

[SSerenity]

This is stated in Princeton Review Hyper Learning. If this is true, how do our blood vessels dilate after they have been constricted?

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[loltopsy]

I think you mean to say "how do our vessels constrict after dilating?". The answer is the lack of vasodilation stimuli plus the following:

https://en.wikipedia.org/wiki/Vasoconstriction#Factors_and_individual_mechanisms

 

[tdod]

For the original question, the above answer is correct; its like an intersection with only a green light, where the green light is analagous to SNS innervation; you know whether to stop or go (dilate or constrict) based on the presence of the green light.

I think you mean to say "how do our vessels constrict after dilating?". The answer is the lack of vasodilation stimuli plus the following:

https://en.wikipedia.org/wiki/Vasoconstriction#Factors_and_individual_mechanisms

Whether they dilate or constrict depends on where they are located; SNS activation dilates blood vessels near muscles but constricts those in the GI tract, sexual organs, etc. (any organ not involved in the fight-or-flight response).