They just shoved a spiky needle in your vein, how come the blood still stays inside your veins after the needle is taken out, is there no hole in the middle of your vein?
In: Biology
Blood does come out, just not at the same rate it went into the vial. This is because the vial is under negative pressure so it pulls the blood in. Additionally, Veins are under low pressure and are stetchy so that hole close somewhat so you bleed minimally, then you clot to close it the rest of the way.
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