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53 Cards in this Set
- Front
- Back
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What property of cardiac muscle lets us think of it as a syncytium?
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intercalated discs have gap junctions that allow for communication and impulse conduction
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Why is there a delay in conduction between atrial and ventricular muscle?
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the fibrous tissue between the atria and ventricles does not have many gap junctions and impulse is restricted to the nerve fibers
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Why does there need to be a plateau in the action potential of ventricular muscle?
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To allow for time for the ventricles to fill
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What causes the plateau in the ventricular muscle action potential?
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slow calcium/sodium channels and increased impermeability to potassium until repolarization
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What occurs with regard to the potassium channels while the slow calcium channels are open in ventricular muscle fibers?
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potassium permeability is decreased about 5 fold
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Slow calcium channels are open for how long in ventricular muscle fibers?
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.2-.3 seconds
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Refractory period of the ventricles
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.25-.30 seconds
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What is the relative refractory period of ventricular muscle?
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0.05 seconds at the end of action potential where action potential can occur prematurely with a strong signal
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Why does cardiac muscle rely on extracellular calcium concentrations?
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Cardiac muscle relies on T-tubules to move extracellular calcium into the cell to activate sarcoplasmic reticulum (which releases more ca). skeletal muscle doesn't rely on T-tubules are much
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How does calcium recycle itself in the cardiac muscle after contraction?
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some is pumped into the sarcoplasmic reticulum (actively). some is transported out as Na moves in (Na/K pump maintains Na coming in)
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Why is cardiac muscle more affected by extracellular calcium levels than skeletal muscle?
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Sarcoplasmic reticulum in cardiac muscle is less developed than that in skeletal muscle. T-tubules (which bring extra cellular calcium into cell) are responsible for more calcium influx in cardiac cells as opposed to skeletal cells
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The plateau in atrial muscle action potentials is how long?
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.2 seconds
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The plateau in ventricular muscle action potentials is how long?
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.3 seconds
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What is the "duration of cardiac cycle" as a function of "heart rate"
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duration = 1/(heart rate)
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The first heart sound (S1) is caused by ...
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closing of AV valves
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The second heart sound (S2) is caused by ...
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closing of aortic/pulmonary valves (splitting = pulmonary closing a little slower due to lower pressure)
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Increased rate of cardiac cycle decreases systole and diastole. Which is decreased more?
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diastole shortens more than systole
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When rate of cardiac cycle is increased, why does cardiac output decrease?
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Since diastole is shortened, ventricles do not fill as much blood. This leads to decreased stroke volume
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The "a" wave in atrial pressure is caused by ...
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atrial contraction
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The "c" wave in atrial pressure is caused by ...
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ventricular contraction (back flow into atria)
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The "v" wave in atrial pressure is caused by ...
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filling of the atria
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The "c" wave in atrial pressure is caused by the closing of what valves...
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A/V valves
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During isovolumetric contraction of left ventricles, what pressure does the ventricle need to reach before the aortic valve opens?
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about 80 mmHg
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Isovolumetric contraction corresponds with what EKG wave?
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QRS = ventricles contracting
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The "a" wave in atrial pressure corresponds with what part of the EKG?
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P wave is atrial contraction
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Why is it not a big problem if a person does not have atrial contraction?
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80% of the blood gets into the ventricles without atrial pumping.
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QRS waves on an EKG correspond with the closing of what valve?
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A/V valve closes when ventricles begin to contract
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Ventricular volume is lowest at what part of the EKG?
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T wave, after ventricles have contracted
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Ventricular filling is broken into thirds. What occurs during the first third?
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rapid filling
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Ventricular filling is broken into thirds. What occurs during the last third?
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atrial contraction of the remaining 20% of blood
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Isometric ventricular contraction occurs for how long?
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.02 seconds
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What is the ejection fraction?
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% of blood ejected out of ventricles. stroke volume/ end diastolic volume. typically 60%
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What is stroke volume?
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amount of blood ejected. end diastolic - end systolic volumes
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Function of valves
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prevent backflow of blood
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Function of the papillary muscles/chordae tendineae
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prevent bulging of the AV valves into the atrium
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Why do the semilunar valves need to be more tough than the AV valves?
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high pressure in arteries after systole (strong back flow), smaller openings (faster flow), no chordae tendineae
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What causes the incisura in the aortic pressure curve?
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closing of the aortic valve
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minute work output =
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stroke work output * heart rate
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Right ventricle work output is what fraction of left ventricle work output?
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1/6
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What valve closes once the left ventricle has reached its end diastolic volume?
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mitral valve closes
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What valve opens once the left ventricle end systolic volume is reached?
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mitral valve opens
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The preload of the ventricle is equal to the ...
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end diastolic pressure
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The "after load" of the ventricle is equal to the ...
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end systolic pressure in aorta
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In heart failure, when the ventricle may be dilated (have a high pressure due to back-up of blood), is more or less work required to pump this ventricle?
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more work and energy is required
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Efficiency of the heart
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20-25%
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What does the Frank-Starling Mechanism say?
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Increased venous return will lead to increased cardiac output = all blood returned to the heart will be pumped out
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Why does the Frank-Starling Mechanism work?
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Increased venous load distends the cardiac muscles and positions the muscle fibers in a more optimal arrangement to accommodate the excess blood
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Complete inhibition of sympathetics has what affect on heart rate?
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decreases heart rate
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Parasympathetics use what neurotransmitter to decrease heart rate?
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Ach
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Vagus parasympathetics work to ...
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mainly decrease heart rate (also weaken force of contraction)
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High blood potassium levels have what affect on the heart?
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slows down heart (action potential repolarizes more slowly)
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High blood calcium levels have what affect on the heart?
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increase heart rate by helping depolarization
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How does increased temperature affect heart rate?
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increases heart rate by increasing permeability to self-excitatory ions. contractile forces are also increased
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