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94 Cards in this Set

  • Front
  • Back
Function of Arteries:
High pressure transport of blood to organs
Function of Arterioles:
Control and distribution of bloodflow
Function of capillaries:
To exchange nutrients, electrolytes, hormones, etc for waste at peripheral tissues
Function of Venules:
To collect blood from capillaries
Function of veins:
to transport blood back to the heart
When you exercise, what really drives the increased bloodflow to exercising muscle?
Increased RETURN of blood to the heart - regulated by the vasculature; the role of the heart is just to pump out whatever returns to it (Starling's law).
So what determines cardiac output?
A BALANCE between the heart's ability to pump out, and the body's ability to return blood to it.
During exercise what increases return of blood to the heart?
The active muscles vasodilate and so more bloodflow goes back to the heart and increases preload.
So the heart and vasculature are:
How are the pulmonary and systemic circulation related?
Theyre in series
Where is the vast majority of blood in the circulation at any time?
In the veins and veinules
What is the business end of circulation?
The capillaries
What %total blood volume is in:
-the heart
-the systemic circulation
-the pulmonary vessels
Heart = 7%
Syst Circ = 84%
Pulm Vessels = 9%
Of the 84% of total blood that is in systemic circulation at any given time, how much is in
-The veins
Veins = 64%
Arterioles/caps = 13%
What vessels have the biggest cross-sectional area?
What is the velocity of a vessel?
The rate at which blood moves through the vessel
What vessels have the highest and lowest velocity?
Highest = Aorta
Lowest velocity = Capillaries
What vessels have an intermediate but relatively high velocity?
Vena cava
Why is the velocity through capillaries so LOW?
Because they have such a huge cross-sectional area - it gives time for hemoglobin to unload oxygen.
In what vessels is MAP most widest?
In the large arteries
Why is the pulse pressure wider in the large arteries than in the aorta?
Because of
-Reflected waves in circulation
-Propagated pulse
What happens to pulse pressure as you move from large arteres to small arteries and arterioles?
It gets damped and goes away completely
What happens to MAP as you move through the systemic vessels?
It decreases
What happens to flow as you move through the systemic vessels?
It starts to smooth out because pulse pressure dampens.
Why is the smoothing out of flow important?
Because it allows for ideal exchange of nutrients and waste at capillaries.
Where does pulsatile pressure resume after it's smoothed out?
In the pulmonary arteries
What is the MAP you would see in
-The aorta
-Large arteries
-Small arteries
Aorta = 100
Lg aa = 100
Small aa = 100-80
What happens in the arterioles? Why?
Pressure drops from 80 - 30 because this is where resistance is highest
What MAP would you expect in
-All veins
Caps = 30, dropping to 10
All veins = close to 0
What is the Average pressure in the pulmonary arteries?
20/15, or about 18 mean pressure
What describes the relationship between pressure, flow and resistance?
Ohm's law
What is Ohm's law?
P = FR
F = P/R
What does flow and pressure directly relate to?
The diameter of a vessel; Resistance.
What is the "P" in P=FR?
The difference in pressure at the beginning and end of a tube.
If there's REALLY high pressure in a tube, like 1000 mm Hg, at P1 and P2, will there be flow? Why?
No; it's a gradient that drives flow.
What is the pressure gradient that drives flow in people?
Arterial pressure - Venous pressure
What IS blood pressure?
A force, exerted by the blood against any unit area of vessel wall. BP = F/A
What is BP measured in?
mm Hg
What is normal MAP?
100 mm Hg
What is the definition of CONDUCTANCE?
How easily blood flows through a vessel for a given pressure difference.
How is Conductance related to Resistance?
Inversely: C = 1/R
How is Conductance related to Diameter of a vessel?
C = d^4; Conductance increases a LOT - to the fourth power - as diameter increases, because resistance decreases.
If you increase a vessel's diameter by a factor of 2, how will that affect conductance?
Conductance will increase by 2^4 so 2x2x2x2=16 ml/min
If you increase a vessel's diameter by a factor of 4, how will that affect conductance?
Conductance will increase by 4^4 so 4x4x4x4 = 256 ml/min
So if you think about it, what vessels have the larger diameter in general? So which vessels have higher conductance?
Veins - veins have higher conductance; it's much easier for blood to flow through them.
What is Resistance equal to?
8 x viscosity x length
Pi x radius^4
So what happens to resistance as viscosity and length increase?
Resistance increases
What happens to resistance as diameter increases?
Resistance decreases
What is Poiseuille's law?
The equation that describes net flow taking into account the pressure gradient and all components of resistance.
What happens to the resistance equation when inserted into F = P/R to calculate net flow?
It gets turned upside down.
What term describes steady state flow through bloodvessels?
Laminar flow
Where is flow the fastest within a tube of laminar flow?
At the central core
What is the velocity of flow at the edge of a tube in which there is laminar flow? Why?
Velocity = 0 - due to friction of fluid molecules touching the vessel wall
What is the opposite of laminar flow?
Turbulent flow
What is most flow in the CV system?
When does turbulence develop?
At extremely high flow rates
Where would turbulence most likely be seen in circulation?
Around valves and bifurcations in people with diseased structures.
What is the restriction on when Poiseulle's law applies?
Only when flow is laminar
What is the MOST IMPORTANT factor determinining Resistance to Flow?
Vessel Diameter
What affects the viscosity of blood?
The hematocrit
What is the typical viscosity of blood close to?
That of water
When will blood viscosity be
High in Polycythemia
Low in Anemia
If vessels were nondistensible, what would happen to flow as pressure gradient increases?
Flow would increase DIRECTLY PROPORTIONAL to the increase in pressure gradient
How does distensibility alter the way changes in pressure gradients affect flow?
The effect is GREATER than would be expected
Why do changes in pressure affect bloodflow MORE than would be predicted?
Because as pressure increases, the VESSEL DIAMETER increases which reduces resistance. So both components of the equation change!!
What is Critical Closing Pressure?
The pressure required to open a completely collapsed vessel
What is the normal critical closing pressure in the arteries?
About 20 mm Hg
What decreases the critical closing pressure?
Sympathetic inhibition
What increases the critical closing pressure?
Sympathetic stimulation
What are the 2 ways in which the circulation system is set up?
-In parallel
-In series
What parts of the circulatino are in series?
The systemic and pulmonary circulation
What parts of the circulation are in parallel?
The components of the systemic circulation - the arms are parallel to the legs for example.
Why is it good that the systemic circulation is in parallel?
Because resistance is MUCH LOWER in parallel - it doesn't build up like in series.
How do you calculate resistance for a circuit in series?
R1 + R2 = RT
How do you calculate resistance for a circuit in PARALLEL?
1/RT = 1/R1 + 1/R2....
So if you have 3 resistors, each with a value of 5, 25, and 100 respectively, what is the Rtotal if in series? In parallel?
Series = 130
Parallel = 4!!!
So if you add resistance in series what will happen?
The total will be greater than the highest resister
If you add resistance in parallel what will happen?
The total will be less than the least resistor
What are the units for resistance?
PRU's - peripheral resistance units: 1 mm Hg/1 ml/sec
What is the pressure in a vessel determined by?
What is the unstressed volume in
Arteries = low
Veins = high
Why is unstressed volume low in arteries?
Because arteries have high pressure due to low distensibility; so they start to stretch at low volumes, and that is the definition of stressed volume.
How much volume can the veins hold compared to arteries?
5X more
What is the pressure slope on the pressure-volume graph for veins like compared to arteries?
Veins = LOW pressure/HIGH vol
Arteries = HIGH pressure/Low vol
How does sympathetic stimulation and inhibition affect the distensibility of a vessel?
Symp Stim = decreased distensibility
Symp Inhibition = increased distensibility
So in what direction would sympathetic stimulation shift the curve of a vessel on the pressure-volume graph?
To the right - in the direction of veins
What is distensibility?
Vascular compliance, normalized by the initial volume.
What is the equation for compliance?
Change in Volume
Change in pressure
What is the equation for distensibility?
How much blood really makes our MAP? Why?
A REALLY SMALL AMOUNT! Only like 200 ml!! Most of the blood in our vessels is unstressed.
What is Pulse pressure?
Difference between systolic and diastolic pressure
What is mean pressure?
The average pressure
What happens to the contour of the pulse pressure as people age?
Systolic pressure gets higher as the vessels become less compliant, so the slope becomes sharper as systolic HTN ensues.
What does Systolic Hypertension result in?
Damage to the endothelial cells lining the vasculature.