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What are the functions of the circulatory system?
- 1) transport oxygen and nutrients to the tissues
- 2) carry waste products away from tissues
- 3) transport hormones throughout the body
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What percent of blood is systemic circulation?
84%
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What percent of blood is cardiopulmonary?
16%
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Arteries contain what % of blood?
13%
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The venous system contains what % of blood?
64%
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Pulmonary circulation contains what percent of the blood?
9%
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Heart contains what % of blood?
7%
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arterioles and capillaries contain what % of blood?
7%
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What are the 3 functions/characteristics of arteries?
- 1) transport blood
- 2) have strong walls
- 3) have a higher velocity
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What is a major function of the arterioles?
they have the potential to greatly alter blood flow at the tissue level to adjust to tissue needs
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What is the function of the capillaries?
exchange of fluids, nutrients, electrolytes, hormones, etc between blood and interstitial fluid
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What % of your blood is stored in your venous system? what effects does this have on anesthetic practice?
2/3 - anesthetics can cause an increase in venous pooling which can greatly decrease blood pressure
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What structure has the largest cross-sectional area? (aorta, arteries, arterioles, capillaries, venues, small veins, venue cavae) Why?
capillaries - they must carry the same amount of blood / min as the aorta
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Which has a greater velocity - aorta or capillaries?
aorta
velocity = blood flow/cross sectional area
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Is blood flow velocity directly or inversely related to cross sectional area? What is the velocity in the aorta? the capillary system?
inversely. aorta = 33 cm/sec, cap = 0.3 mm/sec
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What is the functional pressure in the capillary beds?
17 mm Hg
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Is the pressure gradient large or small across the arteriolar-capillary junction?
large
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cardiac output is controlled by the sum of what?
all the local tissue flow
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What 2 things does CO respond to?
- tissue demand
- nerve signal input
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What % of blood flow do the kidneys receive?
22%
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What % of blood flow does the liver receive?
27%
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What is the formula for Ohm's Law?
Flow = change in pressure / resistance
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What is the definition of blood flow?
the quantity of blood that passes a given point in the circulation in a given period of time. ml/min
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What is Laminar Flow? (include parabolic profile)
Streamline flow where each layer of blood remains the same distance from the wall
Parabolic profile is the idea that the center has a higher velocity than the outer edge
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What is viscosity?
the degree of slipperiness between layers of fluid
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What are the 4 causes of turbulent flow?
- 1) high velocity
- 2) narrowing of vessels
- 3) sharp turns
- 4) passes over a rough surface
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What is the formula for Reynolds number?
tendency for turbulence is:
diamter - velocity - density / viscosity
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What reynolds number indicates turbulence in even small straight vessels?
2000
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What is the definition of blood pressure?
force exerted by the blood against any unit area of the vessel wall
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1 mm Hg = ___ mm H2O = ___ cm H2O
13.6 mm H2O, 1.36 cm H2O
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What is the definition of resistance?
the impediment to blood flow in a vessel
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What is the definition of conductance?
the measure of blood flow through a vessel for a given pressure difference - the exact reciprocal of resistance
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What does a small change in vessel diameter do to conductance?
drastically increases it
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Why did Poiseulle feel the need to create a new formula for flow?
to account for the parabolic profile during laminar flow
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How does Poiseulle's Law relate flow and radius of the vessel?
flow is directly proportional to the 4th power of the radius
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What is the definition of conductance? what is the typical measurement?
measure of blood flow through a vessel for a given pressure difference. ml/min/mmHg
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What does Poisuelle's Law point out about diameter vs. all other components of flow? (change in pressure, length, viscosity)
diameter has the largest effect on flow
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The radius of an arteriole is determined by what 3 things?
- 1) sympathetic tone (nerve signals)
- 2) local tissue chemical signals (drugs or hormones)
- 3) chemicals from tissues (histamine, prostaglandin, CO2, hydrogen)
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