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7.) Biophysics of Circulation
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Where in the body will we find the smallest aggregate cross-sectional area of arteries?
The aorta.
Where in the body is the velocity of blood the greatest? Why?
The aorta, because it has the smallest aggregate cross-sectional area.
Where in the body will we find the largest aggregate cross-sectional area of vessels? What function does this serve?
The capillaries of the lungs has the greatest aggregate crossectional area. This is important because it means that the velocity of blood is slowest in this area, which is important for gas exchange.
How do you calculate resistance for circuits in series? in parallel?
Series
R = R1 + R2 + R3 + R4 +...
Parallel
1/R = 1/R1 + 1/ R2 + 1/R3 +...
What are the different equivalents of cardiac output?
Left side CO, Right side CO, or venous return.
What is Poiseuille's law?
An equation to relate flow, pressure, and resistance.
Q=(π(P_1-P_2 ) r^4)/8ηL
Q = flow in m^3/sec
P1 and P2 are initial and final pressures
r = radius of the vessel
η = viscosity
L = length of vessel
π/8 = proportionality constant
*Be able to predict the change in flow due to a change in one of the variables above*
What vessels will you find the highest amount of resistance of flow?
small arteries and arterioles. This is because the radius is smaller.
How do you calculate the total peripheral resistance of blood vessels?
TPR = (Paorta - CVP)/CO
TPR = total peripheral resistance
Paorta = aortic pressure
CVP = central venous pressure
This is the resistance of the entire systemic vascular system
How do you calculate the pulmonary vascular resistance?
PVR = (PAP - LAP)/CO
PVR = pulmonary vascular resistance
PAP = Pulmonary arterial pressure
LAP = Left atrial pressure
CO = cardiac output
What are the units for resistance?
mmHG/(ml/min)
How do you measure the total pressure change of vessels in series?
(Pi - Po) = (Pi - P1) + (P1 - P2) + (P2-P3) +...
How do you measure the total flow of vessels in parallel?
Q = Q1 + Q2 + Q3 +...
Ideal fluids have what type of flow?
Laminar flow
Describe the characteristics of laminar flow and compare it to turbulent flow.
Laminar flow:
1.) Lamina is nearest to the wall is stationary, high amount of resistance on the surface of the lumen.
2.) Next layer slides over the stationary layer
3.) Velocity of the fluid increases toward the center
4.) There is little mixing between the layers
5.) Poiselle's law most accurate predicts the movement of fluid in laminar flow
Turbulent flow:
1.) Reduces the flow associated with a pressure gradient.
2.) Flow is disorganized, elements of fluid move irregularly in axial, radial, and circumferential directions.
3.) Frequent mixing between the layers
4.) Flow contains whorls, vortices, and eddies
*5.) Turbulence may lead to vascular disease, ie clotting.*
6.) Poiseuille's law is less accurate with turbulent flow.
What is Reynold's number? How is it calculated?
This is a number that is meant to predict whether or not a fluid is closer to laminar or turbulent flow.
Re= (ρDv)/η
ρ = density
D = diameter
v = mean velocity
η = viscosity
Laminar flow: Re < 2000
Turbulent flow: Re > 2000
What are some causes for turbulent flow?
1.) High velocity flow in tube with uniform caliber
2.) Local obstruction
3.) Abrupt increase in caliber (diameter)
4.) Local obstruction plus increase in caliber
Why is it common to have occlusions in coronary arteries?
These arteries are large in diameter, and compounded with plaque build up they are high susceptible to turbulent flow (high diameter means higher reynolds number). More turbulent flow means higher probability for clots.
True or False: Small arteries are more likely to form clots as opposed to large arteries.
False: Actually a large artery causes more turbulent flow and an increase in the formation of clots.
Define wall tension in a vessel. Include the mathematical expression
This is the tendency for a longitudinal slit in the vessel to pull apart.
T = Pr
T = tension
P = transmural pressure
r = radius of the vessel
True or false: Small vessels more easily develop wall tension than large vessels.
False: Small vessels have a small radius, thus the tension does not build as quickly as in large vessels.
Micro-circulation refers to...
Circulation through arterioles, metarterioles, capillaries, and venules.
True or False: Pressure in small vessels in not significant enough to be a risk for tear.
False: Pressure is significant, even in capillaries.
What is transmural pressure?
The difference in pressure between the two sides of a wall or equivalent separator. (ie the pressure in the lumen vs. the pressure on the surface of the vessels).
Wall tension is more easily developed in what type of vessels?
Arterial large vessels due to radius and transmural pressure.
What aspect of large vessels allows them to withstand high wall tensions? What aspect of small vessels protects them from high wall tension?
Large vessels have elastin in the tunica media that allow them to stretch.
Small vessels have a small radius and thus don't allow wall tension to build easily.
How does an aneurysm contribute to wall tension?
It contributes to an increase in the radius of the vessel (aneurysm). Larger radius means higher wall tension. High wall tension is a risk for rupture.
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