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54 Cards in this Set
- Front
- Back
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The electrical events in the heart ____ cardiac contraction
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initiate
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Fast- response AP
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contracting and conducting cardiac myocytes
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Slow-response AP
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pacemaker cells in the SA and AV node
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Cardiac Myocyte AP
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Fast Response
-generated by the contracting and conducting myocytes -the resting membrane potential is about -90 - -80mV - rising phase is very hast (vertical line) due to Na+ |
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Pacemaker AP
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Slow Response
- generated by pacemaker cells of the SA and AV node -Auto-rhythmic - Resting membrane potential is -60mV - Due to Ca+ influx |
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Cardiac Myocyte AP
- Phase 0 |
Rapid Depolarization
- Rapid Na+ influx through the voltage-gated Na+ channels (Fast Na+ channels) |
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Cardiac Myocyte AP
- Phase 1 |
Early Partial Repolarization
-the efflux of K+, the transient outward K+ current (I to) |
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Cardiac Myocyte AP
- Phase 2 |
Plateau Phase
- Increased Ca++ conductance |
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Cardiac Myocyte AP
- Phase 3 |
Final Repolarization
- the efflux of K+ exceeds the influx of Ca++ |
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Cardiac Myocyte AP
- Phase 4 |
Resting Potential
- is determined mainly by the K+ conductance |
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Effective Refractory Period
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Absolute
Duration: during phase 0,1 and part of 3 -NO AP can be triggered -Voltage-gated Na+ channels are inactivated |
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Relative Refractory Period
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Early in this phase suprathreshold stimuli are required to elicit and AP
-A very strong stimuli can trigger an AP -All Na+ channels still not completely reactivated |
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During the ERP, stimulation of the cell does not generate new AP because
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the fast Na+ channels are inactivated and therefore cannot be reopen
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the length of the refractory period limits?
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The frequency of AP and therefore contractions
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Pacemaker cells: Autorhythmic Cell
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-initiate action potential
-Have unstable resting potentials called pacemaker potentials -Use Ca++ influx for upstroke (phase 0) of the AP |
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SA : ionic currents
-Phase 0 |
upstroke
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SA : ionic currents
-Phase 3 |
Repolarization
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SA : ionic currents
-Phase 4 |
Slow (spontaneous) depolarization
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Pacemaker Potential
- Phase 4 slow depolarization occurs due to |
opening of special type of Na+ channel called the funny current
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Funny Current
(opens when and closes when) |
Na+ channel opens when the cell hyperpolarizes (-60) and closes when membrane depolarizes (-20)
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T-type Ca+2 channels
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in the late phase 4 there is a small increase in Ca+2 through theres channels
- at ~ -50 |
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As potential becomes more postive ______channels begin to open until threshold is reached and many voltage gate Ca+2 channels open
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L-type Ca+2 Channel
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Pacemaker potential: Phase 0 (upstroke)
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-opening of voltage gated L-type Ca+2 channel at -40mV, accompanied by low K+ conductance
-depolarizes towards +132 mV |
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Pacemaker Potential: Phase 3 (repolarization)
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Voltage gated Ca+2 channels become inactivated and voltage gated delayed rectifier K+ channels open
-since K+ dominates, membrane potential moves towards -94mV |
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Refractory Period in Pacemaker Cells
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longer than in contracting myocytes
-Relative Refractory Period extends beyond phase 3 |
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SA node b/min
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60-100
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AV node b/min
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40-55
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Purkinje Fiber b/min
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25-40
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Normal HR
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60-100 BPM
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Max HR
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220-age
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what predominantly innervats the SA and AV node
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Vagus Nerve
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what innervates both the cardiac muscle (predominantly) adn to some (very little) extent pacemaker cells
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Sympathetic nerve fibers
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Sympathetic (NE) stimulate the heart via what receptors
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Beta 1
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Sympathetic stimulation causes postive
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-Chronotropic (increase HR)
-Dromotropic (Increase conduction velocity of electrical impulses) -Ionotropic (increase contractile force) |
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Parasympathetic (Ach) neurons inhibit the heart via what receptors
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M2 receptors
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HR can be reduced by decreasing firing frequency of the:
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Pacemaker Cells in the SA and AV nodes
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The Volume of hte ventricle at the end of the relaxation period
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End-diastolic volume
(EDV) |
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Normal EDV and during exsc
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110-120-normal
as high as 150-180 -exsc |
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The volume at the end of contraction
-the amount "left over" |
End-Systolic Volume
(ESV) |
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Normal ESV and during Exsc
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40-50ml remain - normal
as little as 10-20ml -exsc |
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The amount of blood that was ejected during systole
(EDV-ESV) |
Stroke Volume
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Normal SV and during exsc
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70-normal
as high as 140-160 - exsc |
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In a PV loop
- Initial (passive) tension = |
diastolic pressure
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In a PV loop
- Total tension |
systolic pressure curve
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In a PV loop
- Active Tension |
area between the diastolic and systolic pressure curve
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Contractility
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the capacity of the heart to do work with a constant pre-load and constant after-load
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How is stroke volume altered as a consequence of an increase in pre-load?
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- Increase Stroke Volume
(as predicted by starlings law) - Increase EDV (more filling) with no change in contractility |
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How is stroke volume altered as a consequence of an increase in after-load?
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- Decrease SV (but will see an increase in HR)
-didnt fill it up less, used more work to pump it out, but didnt eject as much -equivalent to an increase in aortic pressure |
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How is stroke volume altered as a consequence of an increase in contractility?
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Increase SV
-squeeze harder (more volume out) -After load the same -There is more emptying |
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Treppe Effect
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Increase frequency also leads to an elevation of contractile force
-greater trans-sarcolemal Ca+2 influx -More Ca+2 in SR available for release |
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% of blood in the venous side
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65%
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% of blood residing in systemic circulation
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85%
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% of blood residing in arterial side
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20%./
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Assumptions of Poisuelle's Relationship
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1. Flow must be laminar
2. Velocity of thin fluid layer at wall is zero 3. Tube is straight, right cylinder wtih constant radius 4. Fluid is incompressible 5. Viscosity of fluid must be constant 6. Flow must be steady |
