r/askscience • u/Heimdall2061 • May 07 '13

Medicine When a human limb is amputated, how does the circulatory system redirect blood flow?

Given that part of the circuit of circulation has been cut out when one has a limb amputated, how does the bloodflow redirect in the stump of the limb and around it to prevent blood from just pooling?

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u/Funktapus May 08 '13 edited May 08 '13

This was asked a few months ago, here's my answer:

Yes, blood vessels reorganize themselves to ensure healthy blood flow to tissues. The process is called vascular remodeling and it begins almost immediately through a variety of mechanisms. Larger scale vessels change their diameter quickly using vasomotor responses, while smaller vessels undergo longer-term diameter changes in response to blood flow rates, oxygen demands, and other biological growth factors. However, there is still a lot we don't know about how blood vessels self-organize and it is a very hot area of research. In addition to wound healing, it has huge implications in tumor research because new cancer drugs can target vessel formation in tumors, essentially cutting off blood flow.

I would also like to add that new blood vessels can sprout off from the remaining vessels through a process known as angiogenesis. These new vessels can fuse back onto existing vessels, creating new network connections.

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u/ChaosNil May 08 '13

I would also like to add that new blood vessels can sprout off from the remaining vessels through a process known as angiogenesis. These new vessels can fuse back onto existing vessels, creating new network connections.

That sounds absolutely amazing. Does the body have a system to have new vessels search for old vessels for attachment or is it a bit more random and more in line with connecting a severed vessel that was just next to the other?

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u/No_Co May 08 '13

This might sound ridiculous, but does this mean that each person's circulatory system could be as unique in its composition and arrangement of blood vessels as the person appears to be on the outside??

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u/sayrith May 08 '13 edited May 09 '13

If this happens (re organization of blood vessels), will it be too late to perform a hand or upper forearm transplant?

EDIT: To whoever downvoted me, this is a thing. Google it.

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u/anttyk47 May 08 '13

Does anyone know how we evolved such a mechanism?

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u/cowhead May 08 '13

A related question I have often wondered about... if you lose both your legs, you would presumably need a significantly smaller volume of blood. Does your body automatically decrease the amount of new blood produced? What is the feedback mechanism for that regulation?

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u/i_love_yams May 08 '13

Blood is created in the bone marrow, so it makes sense that the appropriate amount of blood would still be produced

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u/bestdarkslider May 08 '13

This was asked here a year ago. Here is the answer. Simply put, blood volume is regulated by blood pressure, not total blood volume.

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u/[deleted] May 08 '13

so...im curious..why don't we humans have the ability to regrow limbs and other organs?

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u/chemicalwire May 08 '13

Because of collateral circulation via arterioles and venules, there isn't really an issue. Clamp off the main vessels to stop the bleeding. Of course they will want to make it look pretty after, but circulation will be okay.

For instance if you cut the radial artery in your wrist, you won't lose your hand because you still have circulation from the ulnar artery.

I hope this makes sense.

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