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scoliendo OP t1_ituatr8 wrote

Reply to comment by auraseer in How does vasoconstriction reduce blood pressure in haemostasis? by scoliendo

That's what I thought, but apparently when a blood vessel is injured, the vessel constricts in order to reduce blood pressure, which is the opposite of my understanding. Hence the question.

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auraseer t1_itubsvr wrote

It reduces blood pressure very locally at the site of the injury, increasing it elsewhere.

Imagine you have a cut on your hand. In response, the arteries in your wrist constrict. That constriction means they become narrower pipes, which means blood cannot flow through them as easily, which in turn means there is less blood inside your hand. Therefore, the blood pressure specifically in your hand decreases.

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scoliendo OP t1_ituc714 wrote

So as I hypothesised, the vasoconstriction is occurring proximally to the injury in order to reduce blood flow and hence blood pressure at the site of the injury. Thank you! I just wish my texts had made this more clear - they all state it as though the vasoconstriction is happening AT THE INJURY SITE.

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auraseer t1_itud5ph wrote

Now that you understand that part, I'll admit I was oversimplifying slightly.

Vasoconstriction is happening all around the region of injury. It's not really affecting just that big artery in the wrist. It's affecting all the little arteries and arterioles near the wound.

Constriction proximal to the injury will reduce blood flow to it, no matter how far proximal. It will work even if it's just happening in the arterioles a few centimeters or millimeters away from the injury.

That's what they mean by "at the injury site."

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