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### 38 Cards in this Set

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 What is laminar flow? Where is it fastest? Slowest? *Fluid moving with a parabolic front. *It is fastest at the center *it is slowest at the edges Pouisielle's law can be reduced to an expression of R and radius. How are these two related? What does this insinuate? *R = 1/r^4 *that radius is the primary determinant of resistance What keeps changes in capillary bed resistance from having drastic effects on MAP? The fact that most beds are arranged in parallel circuits buffers the effects on MAP. What effects will dilation of a capillary bed have? Lower R and increased Q and P in that capillary, but small effects system-wide. What effects will constriction of a capillary bed have? *increased R and decreased Q and P in the capillary bed *buffered effects systemwide What is the equation for velocity of blood? v = Q/cross-sectional area What happens in a transition from a smaller vessel to a larger vessel? Velocity drops, which can result in pooling and increased pressure on the vessel walls. Why is velocity slowest in the capillaries? What beneficial effect does this have? *Because the total cross-sectional area of the entire bed is taken into account. *Slow velocity allows good exchange with tissues In words, how is tension defined by the LaPlace relationship. Tension is the force a wall must generate to counteract the pressure inside. What is the equation for tension? T = Pr/h *h = wall thickness What happens to tension in the event of an aneurysm? The radius of the vessel inceases, thus tension increases. In arteries, there is both high pressure and a large radius. How do these vessels prevent a high tension? By their thick walls (high "h"). How do capillaries withstand pressures up to 100mmHg? The radius is very small, this reduces tension and also allows the capillaries to have very thin walls. In HTN, pressure in the arteries increases greatly. How do the arteries compensate? There is hypertrophy of the wall and an increase in "h" - this reduces the tension on the artery. In aortic regurgitation, blood flows back into the LV and increases LVEDP. How is this exacerbated by the LV? How is it compensated for? A stretching or dilation of the LV increases "r" and thus increases T even more. The LV compensates through hypertrophy of the walls. What effect would a LV MI have on the tension in that area? The loss of myocytes would cause an aneurysm, thus increasing "r" and tension in that area. The risk for rupture increases. Define diastolic wall tension (as experienced by the LV). The distending force that must be overcome by contraction of the myocytes in order to compress the LV. What is atherosclerosis? What effects does it have on systolic pressure? Why? *stiffening of arterial walls *increases systolic pressure *vessels are less able to stretch and recoil What is pulse pressure? PP = systolic P - diastolic P Name 3 determinants of systolic arterial P. How is each related to P? *SV, directly related *diastolic P, which determines the starting P *CPL, inversely related How would an inotropic rx affect systolic and diastolic arterial P? *would increase SV (thru CTY) *large rise in systolic P *modest rise in diastolic P What are the three main determinants of diastolic arterial P? How is each related to P? *SVR, directly related *systolic P, determines starting P *HR, directly related - determines time for draining before next surge in P What happens to pulse pressure when SVR decreases? It increases. Decreased SVR means diastolic arterial P drops, but systolic pressure remains unchanged. What happens to pulse pressure when SV increases? It increases. Increased SV causes an lg increase in systolic arterial P, but only a modest increase in diastolic P. How would tx with an arteriolar vasoconstrictor affect pulse pressure? It would decrease. SVR increases, thus so does diastolic arterial P. Systolic P inceases only modestly. What are two synonyms for CPL? How can it be defined? Distensibility or capitance. The change in volume for a given change in pressure. What is the equation for CPL? CPL = delta V/delta P (the change in volume for a given change in pressure) Which have greater CPL - veins or arteries? Veins - they are elliptical and not totally filled. What 2 things are the main determinants of CPL? Passive structural components and active vascular smooth muscle. How does contraction of VSM affect large arteries and veins? It stiffens walls, but normally does not decrease diameter. How does sympathetic excitation of veinous smooth muscle maintain SV? It decreases CPL, which maintains or increases veinous return to the heart. List the 6 main determinants of CVP. 1.Constriction of venules and sm. veins 2.decreased CPL in lg veins 3.Total blood vol. 4.Gravity 5.Capillary P. 6.CO How does gravity affect arterial pressure below and above the heart? *Below the heart, G can add 90mmHg of P *above the heart, G can subtract 30mmHg Which is affected more by gravity, venous or arterial circulation? Why? Venous - b/c of the greater distensibility of the vessels. What are 4 mechanisms venous circulation uses to counteract the effect of gravity? 1.Contriction of VSM reduces CPL 2.Increase arterial pressure 3.Skeletal muscle compression 4.movement of diaphragm How does decreased CPL affect CVP? It increases it. How will constriction of small veins and venules increase return to the heart? There are 2 reasons. 1.Increase CVP 2.Reduce to volume of the venous reservoir - i.e. mobilize more blood Why does a decrease in CO raise CVP? Decreased CO creates a backlog effect that translates into greater CVP.