Why do people faint after giving Blood?

Today, my school had a blood drive like they have every year. I couldn't do it since I'm a year too young. You have to be 17.





But anyway. I heard of a few people who passed out during it or after. And people puking afterward. Why do people pass out (not from the sight of blood) after giving blood? And what causes them to throw up?





I'm doing it next year :)





And how much blood is in the human body who is 6'?





And what would happen if they take a little bit too much blood? Could you like die or something?



When you donate blood, it reduces your blood volume. Your volume quickly goes back to normal when the missing blood is replaced by fluid, but if you stand up quickly right after donating, a small number of people will lose consciousness.





You can lose a third of your blood volume, and still be able to stand up and walk around. You'll look like death warmed over, and be pretty white, but it isn't going to kill you. So just taking a pint at donation time isn't very dangerous. If you lose too much blood, you will go into shock and die.





The average adult has about five quarts of blood.




Your body has to work hard to replace what has been taken. Giving you a tired and groggy feeling. People react differently than others. Some cant walk for a little while. Some pass out. Some puke. No big deal it just sucks. But it shows the dedication humans have for one another.




Fear Factor, Bubba! Some people pass out at the very thought of a needle being stuck into their arm. I've seen Mucho Macho men you wouldn't think would be afraid of ANYTHING bite the dust when a little teeny, weeny needle gets stuck in their arm for a blood test.




yeah you do because you just lost all that blood and oxygen so your body has to get back into its natural rhythm. it really hurts to give blood kid and your a pretty big guy(tall) so thats gonna be a lot




They just can't stand the sight of blood, I guess.