This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
All of the following are impoant in determining blood viscosity except? 
Select and explain. 
A. Hematocrit, B. Plasma protein concentration, C. Shear rate, D. Systemic aerial blood pressure
D: Systemic aerial blood pressure
Answer: D: Systemic aerial blood pressure 
Explanation: Blood is a non-Newtonian fluid, that changes viscosity with velocity of blood flow. The major determinants of blood viscosity are hematocrit, plasma protein concentration and shear rate or blood flow velocity. These effects are paicularly noticeable when the paicle size becomes "large" in relation to the vessel size. Red blood cell-vessel effects become measurable when the lumen diameter drops below 1 mm and become impoant in the microcirculation when the lumen diameter decreases to 100--200 um.