system
Given the following post, respond as if you're commenting on Reddit:
human
When someone loses a limb, how do the arteries and veins form a closed circuit again once the wound has healed?

Once the severed arteries/veins are closed off to stop bleeding by the healing process, the heart would keep pumping blood along the previous complete circulatory system and when blood reaches the closed off part of the artery, it has nowhere to go. Similarly the vein exiting from the wound will never have blood in it again. Will the circuit complete itself somehow? If so what is the mechanism used to find the openings of the respective major artery and vein and how do they join?
gpt
Arteries and veins are not connected end-to-end like plumbing pipes. 

As an artery gets further from the heart, it constantly has smaller and smaller vessels branching off from it. Those vessels themselves branch smaller and smaller, eventually becoming the microscopic capillaries. 

At the opposite end of capillaries it's the other way around. They join together into tiny veins, and then larger and larger veins. 

So blood entering your arm doesn't all go to the end of your finger and then turn around. Instead, it perfuses the capillary bed all through your arm. Some blood makes it as far as your fingers, but other blood goes through the capillaries of your forearm or your bicep, and then makes the return trip.

If you amputate your hand, the capillaries in the rest of your arm are all still there. Circulation through them continues to happen just as it always did. The only difference is in pressure, because now there are fewer capillaries being fed by the same size artery.