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MedicineWhen a human limb is amputated, how does the circulatory system redirect blood flow?(self.askscience)
Given that part of the circuit of circulation has been cut out when one has a limb amputated, how do...
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This was asked a few months ago, here's my answer:
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?
The sprouting vessels are guided by growth factors. These would typically lead the sprouts into tissues that are low on oxygen. It is there that two sprouts are likely to meet.
There is some evidence that macrophages, which are traditionally considered part of the immune system, actually help tip cells find each other, acting like little shepherds that help bridge the two sprouts.
http://www.ncbi.nlm.nih.gov/pubmed/20404134
Question: what are "growth factors?"
Growth factors in this context are actually signaling molecules that tissues produce when they run low on oxygen. They create a chemical gradient that vessels like to migrate up.
VEGF is the big one for angiogenesis
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Restore AllHide UnarchivedWhile this makes sense, what you describe are factors that affect growth, but "growth factor" has a specific meaning in biology, and so using the words in a more general way will lead to confusion.
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Restore AllHide UnarchivedEven more interesting is that this is one of the key mechanisms for the metastasis of tumors. Once they hijack the process of angiogenesis, they start shunting more blood (thus more nutrients, oxygen, etc) to themselves in order to grow bigger and nastier that much faster.
Huh, that is interesting. I always assumed that it just sorta took a single cell that started multiplying. I wasn't thinking that it would also impact the other functions around it for that.
it helps to figure that cancer isn't really a cell that has gone bad, but a process.
the body is full of processes and procedures that make it work automatically. cells are born and die according to these processes and rules, they respond to hormones and factors according to the plan, and so on.
but what if one part of the process goes wrong?
what if the parts of the immune system that attack threats is working fine, but the parts that give or create targets go wrong? that's an autoimmune disease.
The processes that cause swelling to fight infection works right - but the process that decides some random particle is to be ignored or fought doesn't work? that's an allergic reaction.
Cancer is caused first because a part of the cell that keeps watch for mistakes in its own code gets broken. If it can't fix itself (or kill itself for the good of the whole) those mistakes will continue to build up. this happens a lot, but usually doesn't cause a problem.
but if that cell, which is now prone to mistakes, alters the processes that control it's growth, it could grow out of control.
the vascularization process would be working fine, but it's job is to get nutrients to areas that need it, and when it notices a crowded, resource starved ball of tissue, it tries to work on it... not knowing that the tissue is a dangerous cancer.
then if the factors get set right, the cells can start to lose their cohesion and flake off of the cancer and get to the blood stream. everything else is automatic, even as the dangerous cells get pushed around the blood to other parts of the body.
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.
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??
It's not ridiculous and is true for the most part. A good example is to look at the veins in people's hands (the back) they're all different and some hand scan technologies actually scan for blood vessels to ID the person.
Also note the issue that some nurses/doctors have finding veins. They aren't always at the exact same spot, and some are deeper or more superficial.
That's a pretty good comparison. Everything's vaguely in the same place, (similar to how you don't have a nose on the back of your head), but with slight personal differences.
I can't honestly speak much about amputations or other extreme pathologies... I don't know much about medicine. Vascular biologists learn a lot from looking at the formation of blood vessels in the retina (which are easy to see even in live organisms).
My field is chemical engineering/tissue engineering, so I actually try to recreate blood vessels from scratch and study how grow and adapt in vitro.
My pleasure.
Overview of strategies used to grow vascularized tissue
Regrettably cool study that was published by our rival research group.
Interesting review on how blood vessel circuits optimize their diameters
I love your title for the second article. And it was a cool study!
Just been awarded a place on a DTC PhD course in Leeds, UK studying tissue engineering. Extremely excited! How has your experience of the field been?
Congratulations! I'm still in my first year, but it has been challenging. My undergrad was in ChemE, so I'm used to modeling distillation columns and chemical reactors on engineering paper. Making the transition to culturing mammalian cells has been wild. Discussions like this where everyone is so excited are what keep me going, though. It really is a beautiful topic.
Does anyone know how we evolved such a mechanism?
Some of our ancestors got lucky. The rest did more dying.
Edit: Actually the ones who died weren't our ancestors.
They could have reproduced before they died.
Natural selection.
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Restore AllHide UnarchivedSo the surgeons tending to a cut-off lower arm don't tie the exposed artery and vein ends into a "U-turn"?
For an above the knee amputation, many of the vessels can simply be ligated and left at that. The process the body uses is much simpler than neovascularization which seems to be getting upvoted in this thread for some reason.
The resulting pressure from a ligated dead end will increase vascular resistance greater than that of the systemic circulation. since blood is a fluid in a closed system, it loves to take the path of least resistance, and will simply bypass the ligated small arteries. Venous blood are capacitance vessels and can distend a large amount before reaching this point. Same principle applies however. After a while, you'll get thrombus formation in those vessels and you'll essentially have a plug where the blood isn't flowing.
Thanks, that was very useful and gnaw-worthy info. I also appreciate the fact that you took a break from vital studying to contribute.
Nooooo, that would create a high flow shunt, bypassing the normal resistance of the body.
What's all this I hear about high flow shunts? I tried Wikiing it but to no avail. Don't I want fast veins for my fast lifestyle? What's the catch?
How long does it take to make a new vessel? Minutes? Hours? Days? Weeks?
Depends on a lot of things, but probably a few days for clear new vessel formation.
Is there anything that theoretically could be done to enhance this proccess before a limb is amputated?
You can lick it.
When there is a blood clot why don't blood vessels reorganize around it?
They do, it just takes time.
Is cutting of blood flow still considered as a successful therapy? No expert here, but thought that it makes tumors more aggressive and stimulates spreading through the body.
Restoring oxygen levels to normal apparently makes them more sensitive to treatment. http://www.dailymail.co.uk/health/article-1203600/Injecting-oxygen-cancerous-tumours-improves-chances-recovery.html
Antiangiogenic therapies have a rocky track record. It's a complicated topic, but basically, tumors have WAY too much angiogenesis to begin with. Lowering the angiogenic activity actually makes their vasculature more normal and 'healthy.' The silver lining is that these healthier vascular networks can deliver chemotherapy to the tumors better.
In essence, antiangiogenic therapy has to be used in conjunction with traditional drugs and it's a pretty late-stage treatment.
What happens when the vessels on the blood-brain-barrier get blocked?
Say if someone smoked paint or somehow introduced a lot of heavy metals into their bloodstream which would get stopped at the blood brain barrier.
The blood brain barrier isn't like a sieve, it's a difference in the capillaries in the brain. Big molecules just keep on circulating in the blood stream instead of being able to diffuse out into the extracellular fluid.
If blood vessels in the brain get blocked, as happens with clots or other emboli, the result is a stroke.
Oh. I always was under the impression there was some barrier in the carotid arteries.
So the barrier is the capillaries & vessel walls themselves inside the brain? They're structurally different than those in other areas of the body?
Correct. The capillaries in the brain have tighter junctions between the cells so that larger molecules are trapped in the blood stream, and just pass on through.
baroreceptors cause vasoconstriction upon rupture of blood vessels in order to bring back to normal blood pressure.
Then why doesn't the body begin to do this when there is a build up of cholesterol near the heart? What triggers the angiogenesis? It seems like we have the means within our body to avoid bypass surgery, so I wonder why our bodies don't do that.
How big does a wound need to be before there is evidence of vascular remodeling?
How long after amputation can you reattach a limb?
What effect does amputation have long term on cardiovascular health? Say if someone was like a quadruple amputee. Would they have to worry about clots as much as someone with legs? Or would their heart weaken since it doesn't have to pump as much blood or pump it as far?
You say it's a hot area. How does one research?
Most of it is medicine related. The biggest application by far is tumor angiogenesis. Doing medical research (MD/PhD program) or biomedical engineering research (PhD) would be a safe bet for that.
There are also a couple of us in peripheral disciplines (chemical engineering) that are getting involved in vascular tissue engineering.
But does all research involve cutting a limb? I'm wondering on behalf of the animals.
Cutting of limbs is unlikely, as that is a very indirect way of getting information about vessels. More likely, researchers will look at the blood vessels of the retina and how they develop under different conditions.
Conversely, we can now grow blood vessels basically in 'test tubes' and watch them grow without any animal.