Cardiac Physiology

Question 1

Resting membrane potential of cardiac myocyte set by which ion?

Answer 1

Potassium.
Vm = -85 mV.
Ek = -89 mV

Question 2

Phases of the ventricular action potential

Answer 2

0) Upstroke (inward Na current)
1) Notch (Inward Ca current)
2) Plateau (Rapid inward K, slow inward K)
3) Repolarization (rapid inward k, slow inward K)
4) Resting Potential (Inward rectifying K)

Question 3

Phases of the SA nodal action potential

Answer 3

0) Upstroke (Inwards Ca current)
2) Plateau (inward ca current)
3) Repolarization (slow and rapid k current)
4) Slow depolarization (funny current)

Question 4

Which current has faster phase 0?

Answer 4

Ventricle (because serious Na current)

Calcium current is much slower in SA node.

Question 5

Is IK1 present in SA node?

Answer 5

No, only in ventricle. That’s why there is a steady membrane potential.

Question 6

Parasympathetic effect on heart

Answer 6

Decreased chronotropy, decreased dromotropy (cell-cell conduction)

Question 7

Sympathetic effect on heart

Answer 7

Increased chronotropy, increased inotropy, increased dromotropy, increased lusitropy

Question 8

How does the parasympathetic system decreased chronotropy?

Answer 8

Activation of acetylcholine-dependent K current.

ACh binds, GPCR BG subunit opens SA nodal K channel. K rushes out and slows the progression of the funny current (repolarizing).

Question 9

How does B-stimulation increase chronotropy?

Answer 9

Increases cAMP, which opens up HCN channel more (which controls the funny current)

Question 10

How does B-stimulation increase inotropy/lusitropy?

Answer 10

Activates PKA which phosphorylates L-type Ca channel, phosphorylation of PLB which increases Ca in serca.

Question 11

What effect does parasympathetic stimulation have on the ventricles?

Answer 11

None.

Question 12

MAP=?

Answer 12

=COxTPR

=SVxHRxTPR

Question 13

CO=?

Answer 13

=SVxHR

Question 14

Baroreceptor reflex and its response to ie hemorrhage

Answer 14

Attempts to keep MAP the same when it changes.

If hemorrhage occurs, CO decreases, MAP decreases. So, baroreceptors will cause increase in HR, increase in contractility, constriction of arterioles (to increase TPR) and constriction of veins (increased preload ->increased CO).

Question 15

How does the baroreceptor reflex constrict arterioles?

Answer 15

Alpha receptors increase IP3, which release Ca from SR.

Question 16

RAA system

Answer 16

Angiotensinogen converted to ANG I by renin (released from juxtaglomerular cells), ANG I converted to ANG II by ACE.

ANG II increases aldosterone, which increases Na+ reabsorption in kidney, which increases blood volume.

ANG II is also a potent vasocontstrictor

Question 17

PV loop

Answer 17

Draw it.

Question 18

What two lines define the boundaries of the PV loop

Answer 18

ESPVR (upper)

EDPVR (lower)

Question 19

How to increase preload? Effect on SV?

Answer 19

Increase blood volume, constrict veins. Increases SV

Question 20

Starling curve

Answer 20

SV against LVEDP. Increase in LVEDP (preload) leads to increased SV.

Question 21

Increasing afterload?

Answer 21

Decreases SV by shifting up the ESPVR

Question 22

How to increase afterload?

Answer 22

Increase TPR (arteriolar constriction), chronic hypertension, aortic stenosis.

Question 23

How to increase contractility?

Answer 23

Sympathetic stimulation, increase in muscle mass.

Decreased by Ca2+ channel blockers, ischemia, B blockers.

Question 24

As atrial pressure increases…

Answer 24

venous flow decreases

Question 25

Things that increase venous return

Answer 25

Increased blood volume, relaxed arterioles (increases maximal flow), constricted veins (increases atrial pressure)