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physiology block 1 > CV physiology > Flashcards

CV physiology Flashcards

1
Q

rates of contraction for SA node, AV node, bundle of his

A

SA node ~ 70
AV node ~ 40-60
bundle of his ~ 30-40

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2
Q

what is overdrive suppression?

A

higher frequency of SA node firing will suppress the other pacemaker cells from firing at their inherent rates bc the AP will pass from the SA node down the conduction system to the other cells before they have the chance to fire

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3
Q

what is the consequence of varied regional conduction velocities in the heart?

A

AV node is the slowest
Purkinje fibers are the fastest
this allows for the AV node to be the “gatekeeper” for the ventricles if the atria are firing too often and it also allows for coordinated ventricular contraction

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4
Q

2 determinants of cardiac membrane potential

A

ionic gradients, ionic permeabilities

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5
Q

what maintains the RMP of most cells?

A

Na/K ATPase

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6
Q

what are the 3 types of channels specific to pacemaker cells?

A

1- Na-HCN
2- t-type Ca
3- K-K(Ach)

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7
Q

what is responsible for the upstroke of AP in SA and AV node pacemaker cells?

A

Ca influx via L-type Ca channels

recall these cells lack Na channels

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8
Q

what limits the extent of hyperpol in pacemaker cells?

A

Na-HCN and t-type Ca channels limit hyperpol to -60 mV

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9
Q

what is the consequence of Ca being the ion to cause upstroke in SA and AV node pacemaker APs?

A

upstroke is slower and lower amplitude

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10
Q

what causes the upstroke in purkinje fiber pacemaker cells?

A

Na influx

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11
Q

what causes the plateau phase?

A

K channels open at max depol allowing for K efflux, but then Ca channels open and Ca influx occurs so plateau results

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12
Q

what is different for APs in atrial vs ventricular myocytes?

A

ventricular myocytes require more forceful contraction so they have longer plateau phases allowing for increased influx of Ca and thus stronger contraction

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13
Q

3 determinants of conduction velocity

A

cell diameter
gap junctions
amplitude of AP
(increasing all will increase velocity)

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14
Q

what is the clinical effect of Na channel blockers?

A

Na channel blockers will decrease the amplitude of AP and therefore will decrease conduction velocity

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15
Q

2 main determinants of HR

A

rate of pacemaker firing

conduction velocity

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16
Q

what causes the refractory period? what reverses it?

A

Na channel inactivation causes the refractory period, repel reverses it

17
Q

discuss the differences in sympathetic vs parasympathetic innervation of the heart

A

sympathetic- diffuse, including SA node and AV node

parasymp- only SA node and AV node

18
Q

sympathetic effects on Na-HCN channels

A 
uses GaS mechanism
epi/NE binds b-adrenergic receptor
g protein activated 
adenyl cyclase activated
increases cAMP
increased cAMP activates Na-HCN channels
activation increases rate of diastolic depol and increases HR
19
Q

parasympathetic effects on Na-HCN channels

A

ACh binds M2 receptor
g-protein activated and inhibits adenyl cyclase
decreased cAMP = decreased activation of Na-HCN = decreased HR

20
Q

differentiate between t-type and l-type Ca channels

A

t-type: open during hyperpol (with Na-HCN)

l-type: open during depol, allow Ca influx for contraction

21
Q

sympathetic effects on t-type Ca channel

A

uses GaS
epi/NE binds b-adrenergic receptor
g protein and adenyl cyclase activated
increases cAMP
cAMP activates PKA
PKA phosphorylates/activates t-type Ca channel
increased Ca influx brings cell to threshold faster and increases HR

22
Q

parasympathetic effects on t-type Ca channel

A

ACh binds to M2 receptor
g protein activated and inhibits adenyl cyclase
decreased cAMP = decreased PKA = decreased HR

23
Q

parasympathetic effects on K-K(ACh) channel

A

ACh binds muscarinic receptor
g protein activates K-K(Ach) channel opening it
increased K efflux = hyperpol which delays diastolic depol and decreases HR

24
Q

what is the main controller of HR?

A

parasymp

25
Q

describe junctional rhythm

A

impulse generated at AV node, travels retrograde and anterograde

26
Q

early afterdepolarizations

A

occur in phase 2 or 3

27
Q

late afterdepolarizations

A

occur in phase 3 or 4

28
Q

what is the consequence of Na channels following cardiac injury?

A

functional Na channels are decreased and thus amplitude of AP and rate of conduction are decreased

29
Q

WPW

A

anatomic accessory pathway allows for re-entry from ventricles to atria, leads to tachycardia

physiology block 1 (5 decks)

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