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Our heart pumps blood out in the arteries to the whole body. When that blood returns to the heart in veins, what makes it flow uphill, against the force of gravity?

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Our heart pumps blood out in the arteries to the whole body. When that blood returns to the heart in veins, what makes it flow uphill, against the force of gravity?

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• Veins have valves in them which prevent the blood from backflowing. If those valves start to weaken, blood can leak backwards in the vein and start collecting in little pools (a problem called venous insufficiency). • The pooling blood enlarges the vein and makes it bulge and twist, a condition we call varicose veins. Spider veins can be caused in the same way, by the blood backing up. They can also be facilitated by • Our heredity, • Sun exposure, and • Hormone changes.

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