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You shouldn't ! As a long-term blood donor (over 35 years) myself, I've never passed out after donating. The amount you donate (500ml) is approximately 10% of your total blood volume - an amount the body can lose without detrimental effect. It's replaced by the body within a few days of donating. Common causes of feinting after giving blood are either (1) they haven't eaten before donating, or (2) haven't rested a short while afterwards. Feinting after donating is a rare event.
Wiki User
∙ 8y ago
Wiki User
∙ 15y agoIt is a self defense mechanism of the body. There is nothing you can do about it. I have seen a Medal of Honor winner pass out when blood was drawn, it sure wasn't because he was scared! The needle going into the blood vessel triggers the effect.
Wiki User
∙ 8y agoNot everyone passes out when giving blood. However, giving blood reduces the amount of blood in the body. Our body detects this and can cause the vagus nerve to react.
The vagus nerve controls blood to the gut and can over react on occasions, to a lowering of blood pressure, by diverting blood to the gut and therefore reducing it to the brain.
The body's reaction to the blood loss can make you scared and trigger a faint. Individuals react differently.
This kind of syncope (fainting) is an automatic reaction of the body, possibly a self defense mechanism.
Fainting (passing out)
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Why can't I chew gum while giving blood?
Some people pass out while giving blood. If you should pass out and inhale your gum, the blood bank staff would have an unreasonable and unnecessary amount of work to do to protect your health.
Why do you feel tired after giving blood?
Usually you probably would not pass out when a little bit of blood is drawn but if large quantities are taken out then your body doesnt have enough blood to function. Your brain needs blood to function as well as all the other organs. Eventually then your body just sends the blood away from places that are not as important and they send it to the heart and brain and eventually that may run out a little and you pass out XD
Are neutrophils elevated after giving blood?
Neutrophil levels can be slightly increased after giving blood
What way does blood normally pass across the placenta?
blood does not pass across the placenta
Can people pass blood cells to each other?
can you pass blood cells during sex
What is born from Medusa blood?
Well, if you get a Medusa's Blood on Howrse, it enables you to make your horse into a Pegasus, giving it wings. Sadly, it doesn't pass through to foals. A lot of Howrse players say that should be otherwise. I will let you decide.
Can giving blood cause numbness in fingers?
Yes, giving blood can cause numbness in fingers however, this is not a normal reaction. If you experience numbness in your fingers after giving blood, you should contact your doctor immediately.
Which blood vessel does blood oxygen pass through?
Oxygen and other gases pass through the capillaries.
You pass blood each time you go to pass feces The blood first before feces?
before
Where do soluble products pass in to the blood?
by pumped blood
How blood pass through the veins?
what veins does it pass through
If you pass a urine test can you pass a blood test?
yes
