Question

What does an vein have that and artery doesn't, and why is it so important?

Answer 1

Veins carry the blood back to the heart. They're similar to arteries but not as strong or as thick. Unlike arteries, veins contain valves that ensure blood flows in only one direction. (Arteries don't require valves because pressure from the heart is so strong that blood is only able to flow in one direction.)

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Answer 2

Explanation:

Your arteries carry oxygen-rich blood from your heart to every part of your body. Veins carry the blood back to your heart.

Veins are a type of blood vessel that return deoxygenated blood from your organs back to your heart. These are different from your arteries, which deliver oxygenated blood from your heart to the rest of your body. Deoxygenated blood that flows into your veins is collected within tiny blood vessels called capillaries.