L5.1 - Blood flow Flashcards
what is velocity?
The rate of movement of fluid particles along the tube
What is the relationship between flow and velocity?
flow is the same along all points, velocity caries with ‘tube’ radius
What is the relationship of velocity & cross sectional area?
velocity is inversely proportional to cross sectional area
What is lamina flow?
velocity highest in centre, fluid stationary @ edge
What is turbulent flow?
mean velocity increases, the velocity gradient breaks down, flow tumbles over all directions, the flow resistance increases as the pressure increases as well e.g. in the aorta (high pressure)
What is viscosity?
viscosity resists the sliding of concentric layers past each other in laminar flow
What is high viscosity / how doe it affect flow?
low central flow (laminar), lower overall average flow
Describe the effects of changes in tube diameter on flow rate
mean velocity proportional to cross sectional area (pi.r^2)
flow = mean velocity x cross S.A.
wider tube, faster flow in the middle
What is ‘resistance’ to flow?
resistance slows down flow velocity
resistance = pressure / flow
Which factors affect flow resistance?
flow & pressure
resistance increases with viscosity
increase radius, decrease resistance to 4th power (Poiseuille’s law)
Describe the relationship between pressure, resistance & flow
pressure = resistance x flow
Describe the effects of combining flow resistance in series
resistance add
total resistance = sum of individual resistance
Describe the effects of combining flow resistance in parallel
resistance lower (more pathways to flow through) reciprocals: 1/total = 1/Ra + 1/Rb
e.g. capillaries
What is flow?
The volume of fluid passing through a given point per unit time
Describe how the distensibility of blood vessels affects the relationship between flow and pressure?
when vessels stretch, resistance decreases
so in higher pressure, more stretch = easier flow
as vessels widen with increasing pressure - more blood enter than out
Describe how distensibility of blood vessels produces the property of capacitance
distensible vessels store blood - have capacitance e.g. veins (carry 65% body’s blood)
so when the body’s metabolic demand increases, then the venous return increases (from capacitance), increasing cardiac output to meet the body’s metabolic demands
Describe the pattern of flow resistance & pressure over the systemic circulation - 1 arteries & arterioles
Blood is at high pressure in arteries (low resistance as pressure doesn’t drop), as it enters arterioles resistance increases as lumen narrows, large pressure drop
flow stays the same throughout
Describe the pattern of flow resistance & pressure over the systemic circulation - 2 capillaries
flow maintains the same, resistance increases, but because of being in parallel the overall resistance isn’t affected
so v small pressure drop
Describe the pattern of flow resistance & pressure over the systemic circulation - 3 venules & veins
flow remains the same
pressure drop low, as low resistance
Why is the pressure in arteries high? what does this tell us?
the pressure in arteries is high because of the increased pressure in the arterioles
the higher arteriole pressure, higher arterial pressure
What happens if the heart pumps more blood but the arterial resistance remains the same?
arterial pressure will rise
When does flow normally become turbulent?
when lumen is irregular
when viscosity is low
when flow velocity is high
low viscosity = high velocity
When do you hear turbulent flow? Where is it heard?
upon auscultation in:
stenotic cardiac valve (narrowed)
atherosclerotic blockage (femoral, carotid, renal, hepatic arteries)
heard in radial artery when taking blood pressure
What is transmural pressure
the pressure generated between inside and outside of a blood vessel
tends to stretch the vessel
What’s the percentage of blood stored in our heart & lungs?
20%
