Vasculature Flashcards
Describe the main features of laminar fluid flow.
– Fluid molecules touching wall adhere move slowly
– Next layer slips over these etc.
– Middle most layers move the most rapid (Parabolic velocity profile)
Describe the main consequences of turbulence on blood flow.
Disrupts flow
Increases resistance
Poiseuille’s law doesn’t hold true
Is turbulence pathological or physiological ?
Can be both.
Give an example of physiological turbulence.
When ejecting blood at high force into aorta, will create some turbulent flow (expansion of aorta allows turbulence to be harnessed).
Define Reynold’s number.
Used to indicate whether flow is laminar or turbulent (i.e. for a given system, there will be a “critical value” for Re, above which turbulence is highly likely.)
Re = ((velocity of flow) x (radius of vessel)) / viscosity
What factors increase Re ? Explain why.
Factors which increase Re/make turbulence more likely:
– High velocity flow
– Large diameter vessels (Larger vessel, more layers we can get in there, more likely disruption where one of those layers get disrupted)
– Low blood viscosity
– Abnormal vessel wall
Is the aorta more likely to have laminar or turbulent blood flow ? Why ?
Turbulent
Highest velocity flow, large radius so turbulent
Describe the main features of the viscosity of blood.
Blood is a thixotropic fluid (increased flow results in reduced viscosity)
How much more viscous is static blood relative to flowing blood ?
100x more viscous
Graph relative viscosity of blood as a function of blood flow velocity.
Refer to slide 5, on lecture “Vasculature”
Give a clinical application of turbulent flow.
When we take blood pressure, you create artificial turbulent flow using a sphygmomanometer cuff.
Describe LaPlace’s Law.
Distending pressure (P) produces an opposing force or transmural tension (T) in the vessel wall (in order to withstand the pressure within it), proportional to the radius (R) of the vessel. T=PR
Describe the implication of LaPlace’s law on arterioles, the aorta, and capillaries.
Aorta: Large radius, has to generate a huge amount of tension otherwise it would rupture (properties of it evolved to withstand it). Hence, thick walls.
Arterioles: small radius (than aorta) and lower amount of pressure (than aorta) which means it is easy to generate enough tension to stop vessel rupturing. Arterioles can have smooth muscle inside walls which can exert increase in tension which can further squeeze radius.
Capillaries: Very small radius and very little pressure, so walls are one cell thick only (tension required is small). This enables the exchange process to take place.
Identify the practical consequences of LaPlace’s law on the control of blood flow.
1) CONTROL OF BLOOD FLOW
– Low tension required to oppose blood pressure in arterioles
– Smooth muscle control of arteriole and precapillary sphincters are the sites of tissue blood flow regulation (can squeeze radius)
Explain how aneurysms happened, keeping LaPlace’s law in mind.
- Bulge caused by mechanical weakening of affected vessel
- Radius therefore changes (in the bulge, radius greater)
- Consequently, tension has to be greater in the bulge, but that’s also the part that is mechanically weakened, so it keeps expanding until it ruptures (because weakened part of the wall means you can’t withstand the pressure within it and the tension just gives way)