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EnchantedCatto OP t1_j9e6mce wrote

Reply to comment by CastorTJ in when a limb gets amputated, how do they stop the flow of blood? by EnchantedCatto

Right, but what happens to the blood still in the vessel? Does it just dry up?

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jackity_splat t1_j9e9hrz wrote

The blood will still flow up to the point where the artery was cauterized. Then it will turn around and go back to your heart just like all the other blood.

I had one of my toes amputated, the blood still works there just like my other toes. That ones just shorter now.

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ruzzophobia t1_j9f4kqx wrote

aren't arteries like some one-way streets? Blood can flow in both directions?

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Georgie___Best t1_j9f9dsi wrote

Yes, arteries take oxygenated blood to the body and veins return deoxygenated blood to the lungs/heart.

But it isn't like a loop where at some point it becomes a vein. The artery splits and branches like plant roots until it's down to the scale of arterioles, tiny vessels which actually spread the oxygenated blood throughout your tissues via capillaries.

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Krail t1_j9hlwx4 wrote

This is making me realize a question I didn't know I had about the circulatory system.

How do the "delivery" vessels connect back to the "return to the heart" vessels? Does blood come out from the capillaries and then get taken up by other capillaries?

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dcs1289 t1_j9huya2 wrote

The blood cells don't actually leave the capillaries if everything is going fine. The capillary bed is basically a mesh of VERY tiny blood vessels - picture two sets of tree roots with the bottom portion of the roots aiming towards each other and connected - arteries (tree trunk on the left of your mental image) diverge into smaller arterioles which diverge more into capillaries.. which merge back together into venules, which merge into veins (tree trunk on the right).

When the blood is moving through the capillaries, exchange of oxygen and nutrients is able to occur through small pores in the cells (or straight across the cells in some cases). The blood cells don't leave the circulation, but the plasma that they float around in can move back and forth through the tiny gaps.

Here's a good picture to describe the mental image I'm trying to verbalize above.

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Krail t1_j9i6e4e wrote

Ahh, okay.

I think I have one more follow up question, about how the nutrients actually get from blood to the cells. I guess it's... capillaries have pretty broad coverage throughout the whole body, right? What's the furthest a living cell is likely to be from any capillaries?

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dcs1289 t1_j9i74cj wrote

Capillaries are everywhere. It's the end point of the circulatory system everywhere, so there are beds of capillaries in basically any living tissue.

Probably the most well-known tissue with poor/limited blood supply is tendons/ligaments - these are connective tissues with a lot of intracellular matrix made up of collagen, and blood supply to these tissues is poor the further you get from the source blood vessel as there is often very little collateral circulation (what it's called when an area has multiple arteries that feed the capillary beds).

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Georgie___Best t1_j9j3r5b wrote

Capillaries are very small. We are talking of a scale where red blood cells might only fit through single file. At this microscale, diffusion/osmosis are what predominantly facilitates the movement of useful stuff out of the blood and into the extracellular fluid/cells, and waste back into the blood vessels to be taken away.

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seto555 t1_j9l45c2 wrote

To add to the other answers. The process of oxygenation of the cells from the capillaries is called diffusion. Basically the capillary wall is thin enough, that it is leaking Oxygen molecules to the surrounding tissues. The rate of oxygenation depends on partial pressure of oxygen and carbon dioxide (and some other factors) in the surrounding tissues, but usually you can't diffuse farther then a few mm's in a living organism.

Diffusion is mostly used by insects as the main oxygenation process since they are small enough to just have some air filled pipes (tracheas) inside their bodies where the oxygen is directly absorbed from the air.

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jackity_splat t1_j9ipqsn wrote

Thanks! This is what I knew happened but didn’t remember enough to explain it. I just know my veins and arteries still work pretty normally.

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Squiggy226 t1_j9hcvpv wrote

Yes that made it sound like the blood gets to the end of the cauterized or tied off artery and then turns around and goes back the way it came. It branches off to the capillaries which then connect to veins for the return trip.

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jawshoeaw t1_j9fr5bu wrote

That’s not how blood works. The blood at the terminal end of a clipped artery will quickly clot

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chairfairy t1_j9ewtc4 wrote

It has a return path through all the branches that come off it before the amputation point.

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Bax_Cadarn t1_j9fbmpq wrote

Close but not precisely. Think of it like a road system. Whdn You drive off a highway going north, You don't use the same way to go south. You need to drive to a smaller road to later rejoin increasingly larger roads until You enter the main flow from another side.

In ither words arteries branch off into increasingly smaller vessels up to the capillaries, then those collect into bigger and bigger veins

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concealed_cat t1_j9hqoeh wrote

But if you're driving down a freeway, and then encounter a road block 3 miles past the last exit, then what do you do? The cars will just accumulate there with no obvious way out of there. If you cut the artery at a location without any branches, there will be some blood there that will just sit in place, won't it?

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Bax_Cadarn t1_j9hqyhn wrote

Some will clot at the end, some will leave by freshly built microscopic roads, some will go up a bit and leave by the past few junctions afaik. For more details, ask a vascular surgeon ;-)

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chairfairy t1_j9ftns7 wrote

The implication was that the branches lead to "increasingly smaller vessels up to capillaries". Not sure where else someone would think they go...

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Bax_Cadarn t1_j9fvpam wrote

You made it sound like the blood would go "nothing to see here" and turn back through the arteries. I made it so people wouldn't get confused.

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