A&P Chapter 14
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A&P Chapter 14
Chapter 14 - circulation, biophysics of pressure, flow and resistance
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
What percent of blood is systemic circulation?
What percent of blood is cardiopulmonary?
Arteries contain what % of blood?
The venous system contains what % of blood?
Pulmonary circulation contains what percent of the blood?
Heart contains what % of blood?
arterioles and capillaries contain what % of blood?
What are the 3 functions/characteristics of arteries?
1) transport blood
2) have strong walls
3) have a higher velocity
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
What is the function of the capillaries?
exchange of fluids, nutrients, electrolytes, hormones, etc between blood and interstitial fluid
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
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
Which has a greater velocity - aorta or capillaries?
velocity = blood flow/cross sectional area
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
What is the functional pressure in the capillary beds?
17 mm Hg
Is the pressure gradient large or small across the arteriolar-capillary junction?
cardiac output is controlled by the sum of what?
all the local tissue flow
What 2 things does CO respond to?
nerve signal input
What % of blood flow do the kidneys receive?
What % of blood flow does the liver receive?
What is the formula for Ohm's Law?
Flow = change in pressure / resistance
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
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
What is viscosity?
the degree of slipperiness between layers of fluid
What are the 4 causes of turbulent flow?
1) high velocity
2) narrowing of vessels
3) sharp turns
4) passes over a rough surface
What is the formula for Reynolds number?
tendency for turbulence is:
diamter - velocity - density / viscosity
What reynolds number indicates turbulence in even small straight vessels?
What is the definition of blood pressure?
force exerted by the blood against any unit area of the vessel wall
1 mm Hg = ___ mm H2O = ___ cm H2O
13.6 mm H2O, 1.36 cm H2O
What is the definition of resistance?
the impediment to blood flow in a vessel
What is the definition of conductance?
the measure of blood flow through a vessel for a given pressure difference - the exact reciprocal of resistance
What does a small change in vessel diameter do to conductance?
drastically increases it
Why did Poiseulle feel the need to create a new formula for flow?
to account for the parabolic profile during laminar flow
How does Poiseulle's Law relate flow and radius of the vessel?
flow is directly proportional to the 4th power of the radius
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
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
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)