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ToxiClay t1_ixxhtub wrote

Arteries and veins are both blood vessels, and the difference depends on what they're doing.

"Arteries" are defined as blood vessels which carry blood away from the heart.

"Veins" are defined as blood vessels which return blood to the heart.

Keep that difference in mind, and you won't be thrown by things like the pulmonary artery, which carries deoxygenated blood, but does so away from the heart.

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notclevernotfunny t1_ixxj73x wrote

Are they essentially the same kind of tissue, the only difference being which direction blood is flowing? Could one theoretically be repurposed as the other if needed, for example?

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Notorious_Rug t1_ixxkghn wrote

No, they're not the same kind of tissue, but they can be interchanged, to a degree. For coronary artery bypass, the saphenous vein (a leg vein) is often used.

Arteries have thicker walls than veins, and a thicker layer of muscle inside them. Except for the pulmonary artery, arteries lack valves. Veins are thinner-walled, with a thinner muscle layer. They also have valves. These valves prevent blood from pooling and flowing backward (gravity and all that), and, because venous pressure is lower than arterial pressure, the valves "help" pump deoxygenated blood back to the heart.

Edited to add that veins and arteries can also purposefully be connected together to create an arteriovenous fistula, for dialysis access. Arteiovenous fistulas can also occur naturally, as congenital defects.

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ToxiClay t1_ixxjp57 wrote

So the answer to both of these is yes but no but kind of.

Your veins have valves in them to prevent blood from pooling backwards along your limbs and trunk due to gravity. Veins aren't driven by the beating of your heart, after all, and the blood is trying to go up against gravity; without the valves, you'd be in kind of a really bad spot.

You can technically use a vein graft to replace a stretch of artery in a pinch -- the valves won't hurt you too much -- but replacing a stretch of vein with an artery would be a majorly bad move.

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