system
Given the following post, respond as if you're commenting on Reddit:
human
Do amputees produce less blood than the rest of us? Or do veins/arteries "stretch" to fit the extra volume?
gpt
They produce less blood. The body doesn’t have a set quota for blood cell production that it tries to meet - your bone marrow isn’t permanently set to produce 5 blood per day or whatever.

Instead your body reacts to the state of your circulation, as detected by stretch receptors and other signaling pathways throughout your body. Not enough oxygen reaching outlying tissues? Produce more red cells. Blood pressure’s too low? Retain more water and try to create more plasma. Homeostasis works based on target conditions, not target outputs.

Removing a limb removes the space that blood needs to fill and removes the sensors asking for more blood, so the body will adjust its output accordingly.