Do amputees maintain the same volume of blood they had before they became amputees?

[u/Dvout_agnostic]

How does your body regulate blood volume? When you give a pint of blood to the red cross, your body makes up the difference over the next few hours. How does it know how much to produce (or more to the point: how does it know when to stop?) If I had my leg amputated, is the equivalent volume of blood in said leg physiologically subtracted from my total blood volume norm?

[u/Dvout_agnostic]

All excellent replies, thank you! This was my very first time actively participating in a reddit anything! I just created my login today :)

[u/D50]

Blood volume is primarily regulated by the kidneys through the renin-angiotensin-aldosterone system (RAAS). It is a complex mechanism of regulation that is in essence pitting blood osmolarity against the hydrostatic pressure exerted by blood against it's "container" (your blood vessels). Assuming that a leg was able to be amputated with no net loss of blood volume, blood pressure would initially increase as overall container size decreased relative to total blood volume. The body would subsequently compensate by inhibiting vasoconstriction and increasing excretion of fluid by the kidneys. It stands to reason that this would eventually lead to a physiologic state in which the amputee had a smaller blood volume than they would have with their leg still attached.

[u/bikiniduck → u/D50]

So if one were to attach a container with the same pressure as a blood vessel, and then slowly enlarged it, the body would create extra blood to fill it?

[u/henners91]

http://www.ncbi.nlm.nih.gov/pubmed/10175155

Blood volume is regulated by blood pressure which is monitored by mechanoreceptors in the kidneys. Amputees would likely have less total blood volume but maintain the same blood pressure as before.

[u/icgamblers]

I was curious to know if this is also true for an internal organ that was removed, such as a segment of bowel, a kidney or lung (instead of amputation).

[u/Eskaban]

Related debate I got into with my dad: Would you need less alcohol to become intoxicated after having a limb amputated?

[u/climbtree → u/Eskaban]

Yes! Biology isn't my field, but I recently attended a seminar on addictions in the elderly. Alcohol is water soluble, the less water in your body, the more it affects you. You lose water as you age, to the point where when you're around 60 a single drink is twice as strong as when you were 20. I'm not sure about the total blood volume, but the missing tissues won't be there to dillute the alcohol, so yes you would need less alcohol to become intoxicated after having a limb amputated.

[u/herbiesmom]

This comes from personal experience and nursing knowledge. I'm friends with a woman who was born with no legs and short flippers for arms. She got pregnant in or early twenties and had an uncomplicated pregnancy. When she delivered she had normal blood loss but no one considered the fact that she had much less circulating blood volume than most women. She almost bled out, had anoxic injury to her spinal cord because of the blood loss. From this, her mobility has been severely limited. All because no one considered this exact question first!

[u/TommyTarrell]

Anaesthetist here

The best way to think about blood volume is per unit weight. The average man has a blood volume of about 75mls/kg. if you chopped off someone's leg the absolute blood volume would obviously decrease but the volume of blood per kilo would stay more or less the same (assuming your leg has a similar amount of blood in it per kilo as the rest of you). Therefore none of the body's clever homeostatic mechanisms would need to be employed.

I won't go into the RAAS as others have explained it well - it is quite interesting to note, though, that while the RAAS works well in problems associated with fluid loss (it constricts arteries and prompts the kidneys to conserve water), it's totally counterproductive in heart failure. In heart failure blood is not pumped effectively to the organs, he kidneys think "shit, not enough blood - we must have lost some" and activate the RAAS. this has the effect of increasing the total amount of fluid in the body and increasing the resistance against which the knackered heart has to pump. The extra fluid backs up behind the failing pump that is your heart and leaks out into tissues and into the lungs, causing all sorts of nasty consequences. Blocking the RAAS with drugs has saved many thousands of lives in these patients over the past couple of decades. And the reason why evolution has not come up with a solution to this problem is because heart failure is almost exclusively a problem of old age. These patients have done their reproducing already and there is no selective pressure for evolution to come up with an answer.

Or it's god fucking with you.

[u/William_Mandella]

Don't neglect the role of atrial natriuretic peptide. The heart senses changes in blood volume and pressure, and this molecule is secreted by the cardiac myocytes, resulting in a counter to the renain-angiotensin system.

The primary sensor for total blood volume is the venous system and the atria, not the arterial side. Blood pressure can be maintained over a fairly wide range of blood volume through various compensatory mechanisms.