Cardiac Cycle Flashcards
Explain the spontaneous depolarization of Phase 4 SA nodal cell action potentials:
(Spontaneous depolarization)
K+ currents decrease
Hyperpolarization activates HCN channels spontaneously and If current increases
Ca2+ increases
Pacemaker cells are capable of self-perpetuation (automaticity) at higher rates due to ________.
Spontaneously “leaky” HCN channels
Phase 0 of nodal action potentials is mediated by ____. Phase 0 of ventricular myocyte action potentials is mediated by _____.
Phase 0 of nodal action potentials is mediated by Ca2+. Phase 0 of ventricular myocyte action potentials is mediated by Fast Na+.
Do pacemaker cell APs, ventricular myocyte APs, both, or neither have HCN channels?
ONLY pacemaker cells have HCN channels.
The HCN channels spontaneously depolarize in pacemaker cells.
Explain what occurs during each stage (a, a–>b, b, b–>c, c, c–>d, d, and d–>a) in this pressure-volume loop:
What are the labeled a, x, c, v, and y zones on this image?
a wave = atrial systole
x descent
c wave = contraction of the ventricles
v wave = venous filling
y descent
Which valve closes first - mitral or tricuspid? Why?
Mitral closes before the Tricuspid because the left ventricle depolarizes/contrasts slightly before the right ventricle.
What closes first, the aortic or pulmonary? Why?
The aortic closes slightly before the pulmonary due to higher pressure in the aorta than the pulmonary artery.
Explain the physiologic splitting of S2:
An important normal phenomenon
In normal physiology, A2 always precedes P2. However, the separation between the two sounds can be so short as to be inaudible—this is usually the case during EXPIRATION and between breaths.
During INSPIRATION, venous return to the right atrium (and hence right ventricle) increases, which delays pulmonic valve closure even further than during expiration. This delay is sufficiently long to be heard as a “Split S2”
What congenital disorder results in a fixed splitting of S2?
Atrial septal defect
(because of an overload in the right heart, cauing a delay in pulmonary valve closure)
What is S3? What causes it?
S3 arises from the tensing from chordae tendinae.
Can be normal in youth, but problematic in adulthood (indicates volume overloaded ventricle aka heart failure).
Occurs in early distole.
What is S4? What causes it?
Sue to contraction of atria (atrial systole) against a stiff ventricle (e.g. in MI and LHV).
Always pathological.
Late diastole.
How is stroke volume depicted on a pressure volume loop diagram?
Which of the following primarily accounts for the spontaneous Phase 4 depolarization of SA nodal pacemaker cells?
A. Inactivation of Na+ channels
B. Rapid closure of Ca++ channels
C. If current through HCN channels
D. K+ influx through Inward Rectifier channels
E. Inactivation of the Na+/K+ ATPase pump
C. If current through HCN channels
Which mechanical event directly precedes (and causes) aortic valve opening?
A. Atrial systole
B. Mitral valve closure
C. Pulmonic valve closure
D. Isovolumetric contraction
E. Isovolumetric relaxation
D. Isovolumetric contraction
Rapid influx of which ion initiates depolarization in ventricular myocytes?
A. Na+
B. Ca++
C. K+
D. Mg++
E. Zn++
A. Na+
Which time period corresponds to isovolumic contraction?
A. F to B
B. B to A
C. A to C
D. C to D
E. D to F
B. B to A
Which of the following waveforms is created by venous filling of the right atrium?
A. a wave
B. x descent
C. c wave
D. v wave
E. y descent
D. v wave
Which of the following points corresponds to the second heart sound (S2)?
A. A
B. B
C. C
D. D
E. E
D
Which of the following points occurs at the same time as an S4?
F
Which component of the EKG tracing directly precedes aortic valve opening?
A. P wave
B. PR interval
C. QRS complex
D. ST segment
E. T wave
C. QRS complex
