Answer
Osmosis helps to maintain blood volume by allowing the body to reach a steady equilibrium. Additionally, in the event that the equilibrium is disturbed, osmosis helps the body to restore original conditions.
Work Step by Step
The number one indicator for blood volume is water (blood is over 90% water by weight). Osmosis helps control where water goes in the body and thus what blood volume.
In the capillaries, the body uses reverse osmosis (capillary filtration) to distribute water and nutrients out of the capillaries and to the tissues. The water cannot stay in the tissues for a long time, it needs to get back into the capillaries and back into circulation (where it can pick up more nutrients). This is accomplished by using larger particles (albumin) in the capillaries. Albumin (and other large particles) cause osmosis to occur and the water to return back into the capillaries from the tissues.
Osmosis is also used by the kidneys for water/fluid retention and control. If the blood volume is too high, a couple of different process occur (including osmosis) and you generally pee out the excess water. If your blood volume is too low, then the body will use osmosis to pull water from the tissues back into the blood and also retain it in the kidneys.
Osmosis helps the body maintain blood volume by allowing the body to reach a steady equilibrium state. Too high or too low blood volume triggers osmosis (and other body processes) to return the body back into equilibrium.
