My understanding and application: Flowing blood with mass m, and velocity v has KE proportional to mean velocity squared as blood flows inside the vasculature, pressure is also exerted laterally against the walls of the vessels So, it is then reasonable to use Bernoulli's for the blood and vessel system: Total E = .5 (density)(v)2 + P + pgy where P is the hydrostatic pressure change in P = density*change in height*gravity So application wise: I been taught blood flow is driven by the difference in total E between 2 points from high to low and since most of the cardiovascular system, KE is relatively low, so the pressure difference can be used to drive flow What I dont understand is if total E gradient is used as the driving force for blood movement, which means that total E is not conserved due to frictional forces, then how can one use the conservation aspect of the Bernoulli's principle to interconvert between kinetic energy and pressure energy for two different points in the blood and vasculature system? For example: a plaque region which decreases the effective diameter of the blood vessel and the region right before the plaque region, with normal diameter. How can you state that the pressure in the plaque region is lower than the pressure in the non-plaque region if the total E is not conserved between those two points? Also, in the Bernoulli's principle will the potential energy density be a significant contribution to the total E throughout the circulatory system? Are we measuring y relative to the bottom of the ground or the center of the body? I have uploaded a practice question that started my series of questions. This question used the conservation of energy of the Bernoulli principle to conclude that hydrostatic pressure was lower in the plaque region that the region right before the plaque region. The total E if as a gradient will have its highest point starting from the location of the heart (the pump) and lowest as it gets farther away from the pump due to friction. Thanks for your help!