Intro to CV physiology

Question 1

What is bathmotropy?

Answer 1

Excitability or threshold of excitation

Question 2

What is chronotropy?

Answer 2

AP emission frequency or HR

Question 3

What is dromotropy?

Answer 3

AP conduction speed or conductibility

Question 4

What is inotropy?

Answer 4

Muscular contraction force or contractility

Question 5

What is lusitropy?

Answer 5

Diastolic relaxation

Question 6

What is tonotropy?

Answer 6

Distensibility

Question 7

What is the average range for a cardiac muscle AP?

Answer 7

200 to 400 msec

Question 8

What is the significance of the long refractory period of cardiac muscle?

Answer 8

Cannot be tetanized
Prevents fatigue
Allows time for heart chambers to fill

Question 9

What are the 10 steps of cardiac excitation-contraction coupling?

Answer 9

1. AP enters from adjacent cell
   2.Voltage-gated Ca++ channels open
2. Ca++ induced Ca++ release from SR through RyR channels
3. Local Ca++ release causes Ca++ sparks
4. Summed Ca++ sparks creates a Ca++ signal
5. Ca++ binds to troponin C initiating contraction
6. Ca++ unbinds from troponin initiating relaxation
7. Ca++ is pumped back into SR through SERCA channels
8. Ca++ is exchanged for Na by NCX antiporter
9. Na gradient is maintained by Na/K ATPase

Question 10

What occurs during phase 0 of cardiac muscle AP?

Answer 10

Opening of voltage gated Na channels
Transient influx of Na

Rapid depolarization

Question 11

What occurs during phase 1 of cardiac muscle AP?

Answer 11

Closure of voltage gated Na channels - Na influx stops
Opening of voltage-gated transient K channels
K efflux - tiny repolarization

Initial rapid repolarization

Question 12

What occurs during phase 2 of cardiac muscle AP?

Answer 12

Opening of voltage gated L-type Ca channels
Ca influx balances K efflux and triggers Ca release from SR
Contraction

Plateau

Question 13

What occurs during phase 3 of cardiac muscle AP?

Answer 13

Ca channels inactivate slowly - decreasing Ca influx
Increased K efflux through delayed rectifying K channel
Repolarization

Late repolarization

Question 14

What will occur during phase 3 is Ach is present?

Answer 14

Ach activates IKAch and increases K efflux
Increases hyperpolarization

Question 15

What occurs during phase 4 of cardiac muscle AP?

Answer 15

RMP is reestablished at -85 mV

Resting membrane potential

Question 16

What are the 4 types of K channels in heart muscle?

Answer 16

Inward rectifying K+ channel (Ik1)
Transient outward K+ channel (It0)
Delayed rectifying potassium channel (Iks, Ikr, and Ikur)
G-protein activated inward rectifying K current (Girk or IkAch)

Question 17

What is the inward rectifying K channel?

Answer 17

Leaky K channel which closes near the end of depolarization and reopen during repolarization

Question 18

What is the transient outward K channel?

Answer 18

Opens transiently at the end of phase 1 and closes during the middle of plateau/phase 2

Question 19

What is delayed rectifying K channel?

Answer 19

Open slowly during the plateau and then more rapidly near the end of phase 2 to initiate repolarization

Question 20

What is G-protein activated inward rectifying K current?

Answer 20

Channel opens in response to Ach release
Efflux of K to cause further hyperpolarization
Reduces effects of If and Ca channels

Question 21

What occurs during phase 0 of SA node AP?

Answer 21

Decreased Ca influx through T-Ca channels
Increased Ca influx through L-Ca channels

Question 22

What occurs during phase 3 of SA node AP?

Answer 22

Increased K efflux through voltage-gated K channels

Question 23

What occurs during phase 4 of SA node AP?

Answer 23

K channels close
Funny Na channels open – Na influx
Slow depolarization of cell
Near threshold funny channels close and T-Ca channels open
L-Ca channels open at threshold

Question 24

What will occur with selective inhibition of funny Na channels?

Answer 24

Decreased HR
No effect on contractility

Question 25

What causes extra systole?

Answer 25

A sufficiently strong stimulus during relative refractory period

Question 26

What is the compensatory pause?

Answer 26

Missed normal systole from the presence of an extra systole

Question 27

What is post-extra systolic potentiation?

Answer 27

Extra volume of blood collected in ventricle during compensatory pause resulting in an increased force of contraction

Question 28

What results in the staircase phenomenon?

Answer 28

When stimuli of same strength are applied at short intervals resulting in increase in height of contraction

Question 29

What is the intrinsic firing rate of the SA node?

Answer 29

70-80 bpm

Question 30

What is the intrinsic firing rate of the AV node?

Answer 30

40-60 bpm

Question 31

What is the intrinsic firing rate of the AV bundle?

Answer 31

40 bpm

Question 32

What is the intrinsic firing rate of the Purkinje fibers?

Answer 32

15-20 bpm

Question 33

What causes the AV nodal delay?

Answer 33

Narrow fiber diameter Relatively few gap junctions Slow depolarization due to slow voltage-gated Ca channels

Question 34

What is the purpose of AV nodal delay?

Answer 34

Allows time for complete ventricular filling Maintains ventricular contraction rate in case of A fib

Question 35

What is the conduction rate of the SA node?

Answer 35

0.5 m/s

Question 36

What is the conduction rate of the atrial pathways and ventricular muscle?

Answer 36

1 m/s

Question 37

What is the conduction rate of the AV node?

Answer 37

0.05 m/s

Question 38

What is the conduction rate of the AV bundle?

Answer 38

1 m/s

Question 39

What is the conduction rate of Purkinje fibers?

Answer 39

4 m/s

Question 40

How does SyNS influence conduction?

Answer 40

Increases

Question 41

How do beta blockers influence conduction?

Answer 41

Decrease

Question 42

How does PsNS influence conduction?

Answer 42

Decrease

Question 43

How does ischemia or hypoxia of the heart decrease conduction?

Answer 43

Decrease

Question 44

How does digoxin influence conduction?

Answer 44

Decrease

Question 45

How to Ca channel blockers influence conduction?

Answer 45

Decrease

Question 46

How does norepinephrine from SyNS work in cardiac muscle?

Answer 46

Binds to Beta-1 receptors Adenyl cyclase increases cAMP increasing PKa Phosphorylation of membrane Ca channels - increases contractility Phospholamban stimulates SERCA reuptake into SR - increases HR Troponin I releases Ca bound to troponin C - quicker relaxation

Question 47

How does Ach from PsNS work in cardiac muscle?

Answer 47

Binds to M2 receptors in atria Inhibits adenyl cyclase Closure of membrane Ca channels - decreases contractility Inactivation of SERCA channels - decreases HR Increases K permeability - hyperpolarization

Question 48

How does ischemia in heart affect conduction?

Answer 48

Katp channels open - increased extracellular K Depolarization Decreases slope of phase 0 Reduced AP conduction velocity

Question 49

How does acidosis effect myocardial function?

Answer 49

Inhibits myofibrillar responsiveness to Ca Decreases binding of Ca to troponin C Decreases force of contraction