Kaplan Section 3 Chapter 1 Cardiac Renal Fundamentals
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| In cardiac cells, in which direction is the Na [ ] gradient? | Na+ outside > Na+ inside --> Na+ flows down gradient INTO cell
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| What are the fast-response fibers in cardiac cells? | In cardiac muscle and in the His-Purkinje system
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| In Phase 0 of the cardiac action potential of FAST-repsonse fibers, which channels open first? | fast I-Na+ channels
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| In Phase 0 of the cardiac action potential of FAST-repsonse fibers, what does the rate of depolarization depend on? | Resting membrane potential of the cell ---(determines)---> # of fast I-Na+ channels open ---(determines)---> rate of depolarization. The more negative the resting potential, the faster the response. As membrane voltage increases, the number of Na channe
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| Which class of drugs blocks phase 0 of the cardiac action potential of FAST-repsonse fibers? | Class I anti-arrhythmic drugs
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| What is Phase I of the cardiac action potential of FAST-repsonse fibers? Talk about the movement of ions. | Overshoot. Na+ channels inactivated. K+ channels open transiently --> K+ flow OUT. Cl- channels open transiently --> Cl- flows IN
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| Which class of anti-arrhythmic drugs blocks phase 1 of the cardiac action potential of FAST-repsonse fibers? | None
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| What is Phase 2 of the cardiac action potential of FAST-repsonse fibers? Talk about the movement of ions. | Plateau. Slow Ca2+ IN. Delayed K+ OUT (I-K channel).
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| Which class of anti-arrhythmic drugs blocks phase 2 of the cardiac action potential of FAST-repsonse fibers? | None
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| What is Phase 3 of the cardiac action potential of FAST-repsonse fibers? Talk about the movement of ions. | Repolarization. Delayed K+ rectifier OUT current increases rapidly as the slow Ca2+ IN current dies out.
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| Which class of anti-arrhythmic drugs blocks phase 2 of the cardiac action potential of FAST-repsonse fibers? | Class III anti-arrhythmic drugs slows the repolarization (makes the slope less steep)
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| What is the slow Na+ current in the cardiac action potential of FAST-repsonse fibers? | Window current (Na+ IN) that lasts from phase 0 through phase 3. Can help prolong the duration of the action potential.
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| What is Phase 4 of the cardiac action potential of FAST-repsonse fibers? Talk about the movement of ions. | Return to resting membrane potential
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| What is normal cardiac resting membrane potential of FAST-repsonse fibers? | -85mV
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| How is the cardiac resting membrane potential maintained in FAST-repsonse fibers? | Na+/K+ ATPase (pumps Na+ OUT and pumps K+ IN)
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| What are the slow-response fibers in cardiac cells? | SA and AV Nodes
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| In slow-response fibers, what does depolarization depend on? | Activation of Ca2+ channels (I-Ca-L, I-Ca-T)
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| Which class of drugs blocks phase 0 of the cardiac action potential in SLOW-repsonse fibers? | Class IV anti-arrhythmic drugs
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| Which channels cause repolarization of the cardiac action potential in SLOW-response fibers? | Delayed rectifier K+ current (OUT)
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| What is phase 4 of the cardiac action potential in SLOW-repsonse fibers? Talk about the movement of ions. | Spontaneous depolarization. Na+ IN (I-f channel), Ca2+ IN (I-Ca-T channel), K+ OUT (I-K channel)
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| Which class of drugs blocks phase 4 of the cardiac action potential in SLOW-repsonse fibers? | Class II and IV anti-arrhythmic drugs
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| What is automaticity in a heart cell? | The ability to depolarize spontaneously.
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| What determines the pace of the heart rate? | The fastest phase 4 slope (steepest slope) of a slow-repsonse fiber, usually, the SA node.
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| What is the effective refractory period? | no stimulus of any magnitude can elicit a response. (i.e. from phase 0 to phase 3 of the cardiac AP because Na+ channels are effectively inactivated because the potential is too "positive" for them to be open)
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| Which types of drugs prolong the effective refractory period? | K+ channel blockers (class II antiarrhythmics)
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| What is the relative refractory period? | a strong stimulus can elicit a repsonse, but the timing will be out of sync with the rest of the heart --L can lead to arrhythmias
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| What do decreases in the effective refractory period of an action potential allow? | longer relative refractory period --> greater chance of premature impulse being generated --> arrhythmia
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| At which membrane potential does the activating (M) Na gate close? | -50mV
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| At which membrane potential does the inactivating (h) Na gate open? | -85mV
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| Why is the rate of Na channel recovery slower in ischemic tissue? | Some cells in ischemic tissue may be depolarized at rest --> dec number of channels able to participate in the next depolarization --> dec conduction rate
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| Which receptors innervate the SA node? | PANS - M2 and SANS B1
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| What is the difference between depolarization in fast vs. slow response cardiac cells? | fast (cardiac muscle/His/Purkinje) -- Na+ influx; slow (SA/AV nodes) -- Ca2+ influx
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| When are Class I anti-arrhythmics least effective? | When Na+ channels are in the resting state (M gates closed, h gates open) -- state dependent
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