A favorite theme on the MCAT for Pouseuille's Law is to see if you understand that because of the extreme effect of decreasing radius on viscous dissipation, the pressure drop per unit length in narrow vessels is much greater than in larger vessels.

From an MCAT writer's perspective, this is the type of concept which you can create an interesting set of answers to a multiple choice question. Furthermore, this consequence of Pouseille's Law is relevant to future doctors. In the cardiovascular system, a major consequence is that the narrow vessels must be much shorter.
Branching vessel

A branching blood vessel.