Heart Physio

Question 1

What is the function of the AV node?

Answer 1

• Acts as a gate to slow the impulses to the ventricles and prevent premature atrial impulses from influencing ventricular rate

Question 2

What do the following portions of EKG wave correspond with in terms of the heart?

• P wave
• Q wave
• R wave
• S wave
• T wave

Answer 2

• P = atrial activation
• Q = His, BB, septal activation
• R = ventricular activation (left)
• S = late ventricular activation (right)
• T = ventricular repolarization

Question 3

S1 and S2 correspond to what?

Answer 3

S1 - closure of tricuspid and mitral valves

S2 - closure of aortic and pulmonic valves

Question 4

What factors affect the threshold of a cardiac cell?

Answer 4

1) resting potential (availability of potassium)
2) excitability (availability of sodium and channels)
3) cell size (hypertrophy, edema)

Question 5

What factors affect the refractory period of a cardiac cell?

Answer 5

1) action potential duration (especially plateau phase, proportional to QT interval)
2) excitability (sodium current, potassium current)

Question 6

Describe phase 0 for the

a) fast response AP
b) slow response AP

Answer 6

• upstroke
  a) fast - sodium current activation, occurs in atrium, ventricle, and His-Purkinje system
  b) slow - calcium current activation, occurs in SA node and AV node

Question 7

Describe phase 1 for the fast response AP

Answer 7

• early repolarization, AP notch
• inactivation of INa
• activation of transient outward K+ current (Ito)
• occurs in atrium, His-Purkinje, ventricular epicardium

Question 8

Describe phase 2 for the fast response AP

Answer 8

• plateau
• inactivation of outward K+ current (Ito)
• activation of L-type Ca current (ICa,L)
• activation of ultra-rapid K current (IKur)
• ICa,L and IKur oppose each other, causing plateau

Question 9

Describe phase 3 for fast and slow response AP

Answer 9

• final repolarization
• slow inactivation of ICa,L
• activation of delayed rectifier K currents (IKr, IKs)

Question 10

Describe phase 4 for pacemaker cells

Answer 10

• inactivation of IKr, IKs

- inward K current provided by funny channel (If); ICa,T; INCX; ICa,L

Question 11

Describe phase 4 for non pacemaker cells

Answer 11

• background K current from IK1 (inward rectifier Kir 2.x channel proteins)
• balance of inward and outward current

Question 12

What is the cardiomyocyte resting membrane potential?

Answer 12

• 90 mV

use Goldman-Hodgkin-Katz to determine, due to multiple ion conductances in cell membrane

Question 13

What are the end effects of hypokalemia on the heart?

Answer 13

• decrease in conduction velocity
• shortens effective refractive period
• prolongs relative refractive period
• increases automaticity
• early afterdepolarizations (reentrant arrhythmias)
• increased excitability!

Question 14

What are the end effects of hyperkalemia on the heart?

Answer 14

• initially increases and then decreases membrane excitability
• decreases action potential duration

Question 15

What are the 3 different junctions for cell-cell adhesion or communication in cardiac cells?

Answer 15

1) desmosome - for mechanical stability
2) fascia adherens - anchoring of thin actin filaments
3) gap junction - site of electrical communication

I think these are all in the intercalated disc? Or together make up the intercalated disc?

Question 16

What are the primary, secondary, and tertiary pacemakers in the heart?

Answer 16

• primary: SA node
• secondary: AV node
• tertiary: His-Purkinje