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hannah posted an update 1 year, 6 months ago
Most veins have valves that open and close. The valves control blood flow and keep your blood flowing in one direction. About 75% of your blood is in your veins. https://my.clevelandclinic.org/health/body/21640-blood-vessels#:~:text=Most%20veins%20have%20valves%20that,blood%20is%20in%20your%20veins.
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