Haemodynamics Flashcards
What is the equation for flow
Pressure gradient between arteries and veins/ resistance
Structure of a blood vessel from inside to out
Lumen
Intima (endothelium)
MEdia (smooth muscle, elastin, collagen)
Adventitia
What is the media made of
Smooth muscle, elastin, collagen
Amount of smooth muscle in aorta, arteries, arterioles and capillaries in relation to each other
0 in capillaries
Most in arterioles
second most in arteries
Not much in the aorta
elasticity in capillaries, arteries, arterioles and capillaries in relation to each other
0 elasticity in capillaries and venules
Elasticity is most In capillaries, second most in arterioles
Smooth muscle content in aorta, arteries, arterioles and capillaries in relation to each other
Most in the capillaries, second most in the arterioles
0 in the arteries and aorta
Relationship between total cross sectional area and the size of the blood vessel
Smaller blood vessels have a larger cross sectional area because they are more numerous
At constant flow rate, which blood vessels have the highest and lowest velocity
Highest- aorta
Lowest- capillaries
What is Flow directly related to
The pressure different
What is flow inversely related to
Resistance
What is resistance determined by
-Length of blood vessels
Viscocity of fluid
-Radius of tube (r^4)
What does the media do
Allow active control over the diameter
What does the adventitia contain and what does it do
Contains lots of elastin and collagen and provides structure
What is there between the media and adventitia and what do these do
Lots of sympathetic nerves
-Control the diameter of the blood vessels
Why should you decrease the blood pressure before the blood reaches the capillary
Otherwise it would rupture the capillary
What control is there not in venules
No dynamic control
How is the flow related to the pressure difference
Greater the pressure gradient, the greater the flow
How is flow related to vessel length
Longer the vessel, the lower the flow (inversely related)
How is flow related to viscosity
Increased viscosity means a lower flow (viscosity means thickness)
Why is the flow being exponentially related to the radius of the tube important (r^4)
A small change in the radius of the blood vessel will have a very large effect on the blood flow
What is resistance largely determined by and why
Radius because vessel length and viscosity doesnt change under normal conditions
What vessels have the greatest capacity to change the radius
Small arteries and arterioles
Formula for total peripheral resistance
arterial-venous pressure
divided by cardiac output
when does turbulent flow occur
When there is atherosclerosis so a higher driving pressure is needed
Why is systolic pressure reduced
Because aorta absorbs some of the energy
Where is the velocity at its max in laminar flow
MAx in the centre
What is elasticity conferred by
Elastin and collagen
What has a smoothing effect on blood
Elastic conduits (arteries) and high resistance arterioles
What does the extent of elasticity determine
The compliance (change in volume for a given pressure)
What does less compliance mean
Less distensibility
What does arterial compliance provide
Provides filtering/smoothing
What does compliance mean
Ability to absorb pressure wave
What does venous compliance provide
Capacity for storage because they have a high compliance
What determines cardiac output
Venous return
What is venous return affected by
- Valves (prevent back flow)
- Constriction of the blood vessels (venomotor tone)
What do constricting veins do to venous capacity and in turn what does this do
Reduce venous capacity which increases return of blood to heart (increases effective circulating blood volume)
What does leg muscle contraction do
Squeezes blood from superficial vein to deep vein to heart
