Vasculature Flashcards
Describe laminar fluid flow
The fluid molecules touching the wall move slowly due to friction, the next layer slips over these fluid molecules but is partially effected by the friction but not to the same extent. Therefore the middle layer of fluid molecules move the most rapid
What accurse as a result of turbulence?
Flow is disrupted and resistance is increased. So posieuille equation doesn’t hold true
What is used to indicate if flow is laminar or turbulent
Reynold’s number (Re). For a given system there will be a critical value for Re, above which turbulence is highly likely
What causes the Re number to increase and make turbulence more likely
High velocity flow, large diameter vessels, low blood viscosity and abnormal vessels wall.
Describe how flow effects viscosity?
Increased blood velocity, decreases the viscosity. Faster the blood flows the thinner it gets
Describe how the blood pressure cuff makes artificially generated turbulence
When blood travels via laminar flow, no sound can be heard. The BP cuff is inflated to pressure above patient systolic so no sound is heard as it occludes the artery. When the pressure in the cuff is equal to patients systolic pressure 1st korotofff sound is heard. The blood in the vessels flows in spirts as the pressure in the artery rises above pressure in the cuff and then drops beyond the cuffed region resulting in turbulence, this produces an audible sound.
What is LaPlace’s Law
Tension = Pressure x Radius. The tension in the vessel walls is what is required to prevent the pressure from the blood rupturing the vessel walls
What are the sites of tissue blood flow regulation
The smooth muscle control of arteriole and precapillary sphincters
Why is low tension required to appose the pressure in arterioles?
Because arterioles have a small radius, the smaller the radius then the lower the tension required as the blood pressure is decreased
Describe the formation of an aneurysm
There is a weakened point in a vessel wall which cannot produce the required tension to appose the blood pressure. So the pressure stretches the wall, increasing the radius and therefore increasing the tension required to withstand the internal pressure. So high risk of rupture.
How to arterioles regulate blood flow
Control regional distribution (The arteriole controls the supply of blood in the area where it is situated)
How do metarterioles regulate blood flow?
They link arterioles directly to venules.
How do precapillary sphincters regulate blood flow?
They vasodilate in response to local factors, increasing the blood flow to the capillary
What are the ways of regulating tissue blood flow?
Active and reactive hyperemia, flow autoregulation, vasomotion and response to injury
Describe what is meant by active and reactive hyperaemia
Active - If tissue is highly metabolically active, the rate of flow will increase
Reactive - Blood flow increases after a tissue has been deprived of blood for a period of time