And that means, in general, changing the radius will affect the resistance much more than if we change the length or if we change our viscosity. So from this discussion, we can basically conclude that our body actually changes the resistance of our blood vessels not by changing the viscosity or the blind length, the blood vessel length, but rather by changing the radius, the diameter of our blood vessel. So it's no surprise that our body uses the blood vessel's diameter to control the resistance. And this ultimately controls the volume of blood that actually reaches our tissue or organ of our body. Now, let's discuss something known as the volume flow rate. So the volume flow rate is simply the volume of blood that passes our blood vessel over some given period of time.