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
It’s a really small hole.
The skin and vein material are both elastic, and fat and muscle around it push back together, so mostly start to close as soon as the needle is removed.
Materials go in or out because of pressure (negative to draw out positive to inject).
When you blood hits either the damaged, not smooth, wall it starts to clot, closing up the wound.
Your blood pressure is only about 1.5 to 3 psi, so not much would come spurting out of an open hole to begin with(contrary to many movies)
Latest Answers