So we have three different factors that determine the resistance to blood flow in a given blood vessel. So factor number one is the viscosity of our blood, and the viscosity is the internal resistance inside the blood that exists because of the attraction between the molecules and particles themselves that are found within our blood. So the more attraction we have inside the blood between the individual particles, the higher our internal resistance is and the greater our viscosity is. And we'll talk about what the actual relationship between Viscosity and the resistance is in just a moment. Now, factor number two that affects resistance is the length of our blood vessel. And factor number three is the radius or diameter of that particular blood vessel.