The Law Posted March 28, 2010 Report Share Posted March 28, 2010 I really had no idea how to answer this and just guessed. Fluids suck! Link to comment Share on other sites More sharing options...
The Ace of Spades Posted March 28, 2010 Report Share Posted March 28, 2010 Viscous flow resistance does cause pressure loss, but the arm is much closer to the heart than the legs are. So the pressure in the arm would be higher, leaving only choice D as correct. Link to comment Share on other sites More sharing options...
The Law Posted March 28, 2010 Author Report Share Posted March 28, 2010 Viscous flow resistance does cause pressure loss, but the arm is much closer to the heart than the legs are. So the pressure in the arm would be higher, leaving only choice D as correct. That's what I was thinking, but it says that the pressure in the leg is the greater pressure. My reasoning was over a longer trip, you're losing pressure to viscous flow and so pressure in the leg is lower. I guess if you think of the body as a closed container and that the weight of blood is building on each other - then the hydrostatic pressure in the leg will be greater because it has more fluid on top of it. That seems really tricky to do though. This is a stupid question lol. Link to comment Share on other sites More sharing options...
estairella Posted March 29, 2010 Report Share Posted March 29, 2010 http://vam.anest.ufl.edu/simulations/bpposition.html I guess if you had known clinically that ankle pressures tend to be higher than arm pressures, you could've chosen that based on exclusion. Viscosity does not play a major role in the large arteries, which is what BP measurements are based on. Link to comment Share on other sites More sharing options...
leviathan Posted March 29, 2010 Report Share Posted March 29, 2010 There is a pressure gradient and it is LOWER as you go distally. However, that is only in a person lying flat where gravity is removed. In standing position as you guys said, the BP is higher thanks to the weight of the fluid. Important to know if you are taking someone's ankle-brachial index! Link to comment Share on other sites More sharing options...
The Law Posted March 29, 2010 Author Report Share Posted March 29, 2010 Haha thanks for the info guys. Gotta love MCAT questions. Link to comment Share on other sites More sharing options...
benhc911 Posted April 12, 2010 Report Share Posted April 12, 2010 maybe its just because im in chemical engineering... but I thought that hydrostatic pressure was well known? deltaP=rho*g*h where rho is the density of the liquid, g is the gravitational constant, and h is the height of the liquid... As such, when you are lower down, there is more blood above you (so to speak), and as such, the h term is greater. g is constant, and since we are comparing blood to blood, the rho term is the same. Maybe I'm starting to confuse what I've learned in Eng from what I learned in basic physics... school is becoming a terrible blur of lack of sleep -___- Link to comment Share on other sites More sharing options...
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