Intro to CV physiology Flashcards
What is bathmotropy?
Excitability or threshold of excitation
What is chronotropy?
AP emission frequency or HR
What is dromotropy?
AP conduction speed or conductibility
What is inotropy?
Muscular contraction force or contractility
What is lusitropy?
Diastolic relaxation
What is tonotropy?
Distensibility
What is the average range for a cardiac muscle AP?
200 to 400 msec
What is the significance of the long refractory period of cardiac muscle?
Cannot be tetanized
Prevents fatigue
Allows time for heart chambers to fill
What are the 10 steps of cardiac excitation-contraction coupling?
- AP enters from adjacent cell
2.Voltage-gated Ca++ channels open - Ca++ induced Ca++ release from SR through RyR channels
- Local Ca++ release causes Ca++ sparks
- Summed Ca++ sparks creates a Ca++ signal
- Ca++ binds to troponin C initiating contraction
- Ca++ unbinds from troponin initiating relaxation
- Ca++ is pumped back into SR through SERCA channels
- Ca++ is exchanged for Na by NCX antiporter
- Na gradient is maintained by Na/K ATPase
What occurs during phase 0 of cardiac muscle AP?
Opening of voltage gated Na channels
Transient influx of Na
Rapid depolarization
What occurs during phase 1 of cardiac muscle AP?
Closure of voltage gated Na channels - Na influx stops
Opening of voltage-gated transient K channels
K efflux - tiny repolarization
Initial rapid repolarization
What occurs during phase 2 of cardiac muscle AP?
Opening of voltage gated L-type Ca channels
Ca influx balances K efflux and triggers Ca release from SR
Contraction
Plateau
What occurs during phase 3 of cardiac muscle AP?
Ca channels inactivate slowly - decreasing Ca influx
Increased K efflux through delayed rectifying K channel
Repolarization
Late repolarization
What will occur during phase 3 is Ach is present?
Ach activates IKAch and increases K efflux
Increases hyperpolarization
What occurs during phase 4 of cardiac muscle AP?
RMP is reestablished at -85 mV
Resting membrane potential
What are the 4 types of K channels in heart muscle?
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)
What is the inward rectifying K channel?
Leaky K channel which closes near the end of depolarization and reopen during repolarization
What is the transient outward K channel?
Opens transiently at the end of phase 1 and closes during the middle of plateau/phase 2
What is delayed rectifying K channel?
Open slowly during the plateau and then more rapidly near the end of phase 2 to initiate repolarization
What is G-protein activated inward rectifying K current?
Channel opens in response to Ach release
Efflux of K to cause further hyperpolarization
Reduces effects of If and Ca channels
What occurs during phase 0 of SA node AP?
Decreased Ca influx through T-Ca channels
Increased Ca influx through L-Ca channels
What occurs during phase 3 of SA node AP?
Increased K efflux through voltage-gated K channels
What occurs during phase 4 of SA node AP?
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
What will occur with selective inhibition of funny Na channels?
Decreased HR
No effect on contractility
What causes extra systole?
A sufficiently strong stimulus during relative refractory period
What is the compensatory pause?
Missed normal systole from the presence of an extra systole
What is post-extra systolic potentiation?
Extra volume of blood collected in ventricle during compensatory pause resulting in an increased force of contraction
What results in the staircase phenomenon?
When stimuli of same strength are applied at short intervals resulting in increase in height of contraction
What is the intrinsic firing rate of the SA node?
70-80 bpm
What is the intrinsic firing rate of the AV node?
40-60 bpm
What is the intrinsic firing rate of the AV bundle?
40 bpm
What is the intrinsic firing rate of the Purkinje fibers?
15-20 bpm
What causes the AV nodal delay?
Narrow fiber diameter
Relatively few gap junctions
Slow depolarization due to slow voltage-gated Ca channels
What is the purpose of AV nodal delay?
Allows time for complete ventricular filling
Maintains ventricular contraction rate in case of A fib
What is the conduction rate of the SA node?
0.5 m/s
What is the conduction rate of the atrial pathways and ventricular muscle?
1 m/s
What is the conduction rate of the AV node?
0.05 m/s
What is the conduction rate of the AV bundle?
1 m/s
What is the conduction rate of Purkinje fibers?
4 m/s
How does SyNS influence conduction?
Increases
How do beta blockers influence conduction?
Decrease
How does PsNS influence conduction?
Decrease
How does ischemia or hypoxia of the heart decrease conduction?
Decrease
How does digoxin influence conduction?
Decrease
How to Ca channel blockers influence conduction?
Decrease
How does norepinephrine from SyNS work in cardiac muscle?
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
How does Ach from PsNS work in cardiac muscle?
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
How does ischemia in heart affect conduction?
Katp channels open - increased extracellular K
Depolarization
Decreases slope of phase 0
Reduced AP conduction velocity
How does acidosis effect myocardial function?
Inhibits myofibrillar responsiveness to Ca
Decreases binding of Ca to troponin C
Decreases force of contraction
