Does the body react to blood donation like hemorrhage?

When someone donates blood, they lose a considerable amount of blood but the body is pretty chill about it (well…YMMV.)

What I’m wondering is why the body doesn’t go into panic/shock about the blood loss like as if you lost the exact equivalent amount via stabbing or shooting? Does the body “know” it’s not in real harm in the blood-donation process and hence not activate the shock response?

See this article on Hemorrhagic Shock. The relevant quote is “Generally, a blood loss of <15% of total blood volume leads to only a small increase in heart rate and no significant change in arterial pressure.”

So the answer to your question is that blood donation isn’t (usually) enough volume to affect you physiologically. Some people will get lightheaded from the volume loss, but the body typically adjusts and re-equilibrates relatively quickly.

The body doesn’t go into panic, the mind does. Some people do panic or faint during blood donation or blood drawing for medical tests, which require even less blood than a donation.

The mechanisms used to close the small wound are the same as for any other small wound (although the ones for blood donation have the decency to be cleaner than many), the mechanisms to replace the blood lost are the same. But for most people, the terror factor simply isn’t there because when we donate blood we do it voluntarily and at an expected time; we don’t make appointments to get wounded.

Thanks. I guess what I was wondering was this:

The rate of blood loss during blood donation is technically a fatal rate (that is, if it continued unabated indefinitely, it would lead to your death.) Your mind knows that the technician will withdraw the needle and tape you up at the right time, but shouldn’t part of your body panic at the ongoing rate of blood loss (the body doesn’t know when this hemorrhage will end?)

Again: the body cannot panic, the mind does. If you want to talk about “going into shock”, please talk about “going into shock”.

And the rate of bloodloss is actually quite slow, we’re not talking “gushing hemorrage” here; the actual amount of bloodloss is also quite small. You seem to think that blood donation is much faster than it actually is.

Have you ever seen an old balloon that got all mushy and deflated? The kind of bloodloss rate involved in blood donation is more akin to the rate of air-loss experienced by that balloon than to that of a balloon that escapes when you’re trying to knot it up (which is what the kind of bloodloss of a major wound would be like). A major wound doesn’t close by itself: the tiny-weeny-little wound involved in a blood donation closes in seconds, and if the nurse was any good leaves as its only visible mark a red dot smaller than a blackhead. I’m not sure if even a hemophiliac would eventually die from such a wound, they’d need to have a coagulation rate of zero.

Yes, it just trickles into the bag, and it’s not a very big bag. Have you given blood? Nothing happens to you. You have a biscuit and a cup of tea afterwards and you are the same as normal.

The body/mind are aware during blood donation that blood is being (relatively slowly) withdrawn by a professional(s) and that it’s a safe procedure. It would not be surprising if there was a totally different reaction involving fight/flight mechanisms if a comparable amount of blood was lost via trauma and (for example) rabid wolves were waiting in the shadows to finish you off.

Says you. I get fresh cheese curds, a selection from a cheese and sausage platter, usually fresh home baked deserts, a selection of flavored coffees, and a glass of water. I’m usually so stuffed I can skip my next meal!

Well, I have to disagree with this statement. I certainly have a reaction but I am used to it and expect it. I’m 65 so age plays a part. I used to recover more quickly.
When I donate (I donate blood every 8 weeks per the recommended schedule) I routinely recline the bed, have an ice pack on my neck, take my time getting up afterward and have a sugary drink. Following that routine avoids any problems. Not doing at least most of that will cause dizziness and some very upset attendants. They REALLY don’t like it when one of their clients reacts poorly to a donation.

Last time I donated my pulse rate was too low and they rejected me until I could present a note from my cardiologist. Which I did. I still couldn’t donate until the next day when a staff nurse just happened to be visiting the donation center that day. :slight_smile:

All I ask for, every time, is if they have a Snoopy bandaid. And they never do. :frowning:

I’d send you a box, but I’m not sure where your “here” is…

Beavis: What do you think they pay for, like, a gallon of blood?

Butt-head:  Just be cool, dude!  Don't take their first offer!

Beavis:  How they do, like, get it out, dude?

Butt-head:  They give you a big knife, then you cut your hand and, like, bleed into a bucket.  Huh, Huh.

Beavis:  Hea hea, that's cool!

Butt-head:  They give you a big old bottle of 'Mad Dog 20/20' to drink first.  Huh, Huh.

Beavis:  High Test!

Butt-head:  And then, when you're done, don't forget to stand up really fast.

Beavis:  Heh-heh-heh.

Butt-head:  If you're lucky, you'll pass out!

Beavis:  Cool!

Yes, but I don’t really think of dizziness as “the body reacting to haemorrhage” in the way the OP is asking (I get dizzy just from lying down and getting up too quickly).
The thing is that the whole enterprise is staffed by professionals who look after you. They don’t let anything remotely like shock happen - any signs that you are going all pale (or whatever) and they’ll stop the donation. They don’t let you leap to your feet, you rest there for a while, they help you up, they give you the snacks and drinks, etc. They would only take a half a bag out of me because I was skinny.
Of course, some people panic and can’t cope with “medical procedures” of any kind and they won’t be accepted or can’t get to grips with it, but as mentioned, panic reactions start with how you feel.

The body’s response is proportional to the damage. Think about this: the only damage is the area in the skin next to the needle. This is quite small and the needle barely does any damage at all going in. It’s a very minor nick and the clotting system has little to do.

That blood is disappearing somewhere is not something the body keeps track of at that local of a level. If in the future someone invents a way to draw blood using teleportation, the body’s response is to first replace the fluids (and electrolytes, etc.) and then produce more cells. All of which takes time and isn’t local.

Isn’t part of the reaction to blood loss through injuries accompanied by physiological effects due to the rapidity of the blood loss? In other words, if someone hacks you with a machete and you lose a pint of blood before the first aid stops the bleeding, doesn’t your body react a little differently than if they draw it out over the course of 20 minutes? As in, during the blood donation example, your body’s BP regulation mechanisms have enough time to kick in and keep BP stable, while in other situations, you may actually experience larger fluctuations in BP.

Sort of. A lot of the data on the body’s physiologic response to blood loss were done by taking blood out of medical students and watching how their BP and HR changed as more and more was taken out. It’s not like physiologists are chopping off legs and waiting to see what happens (in humans). Animal models may be more gruesome but I’m not aware of those studies.

I figured they have a lot of data from military doctors and ERs on how the violent side of blood loss works, and the non-violent side would be relatively easy to obtain (like you describe).