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