Exam 3: Ch 13 Cardiac Cycle in 7 Phases

Question 1

Cardiac Cycle in 7 Phases

Answer 1

Phase 1 - Atrial Contraction   
Phase 2 - Isovolumetric Contraction 
Phase 3 - Rapid Ejection 
Phase 4 - Reduced Ejection 
Phase 5 – Isovolumetric Relaxation 
Phase 6 - Rapid Filling
Phase 7 – Reduced Filling

Question 2

Cardiac Cycle - Atrial Contraction (Phase 1)

Answer 2

• A-V Valves Open; Semilunar Valves Closed
• Atrial depolarization causes contraction of the atria.
• As atria contract, pressure within the atrial chambers increases, which forces more blood flow across the open atrioventricular (AV) valves, leading to a rapid flow of blood into the ventricles.

Question 3

Cardiac Cycle - Atrial Contraction (Phase 1)

- Atrial contraction normally accounts for

Answer 3

• for about 10% of left ventricular filling at rest because most of ventricular filling occurs prior to atrial contraction
  
  • as blood passively flows from the pulmonary veins, into the left atrium, then into the left ventricle through the open mitral valve.

Question 4

Cardiac Cycle - Atrial Contraction (Phase 1)

- At high heart rates, however, the atrial contraction may account for

Answer 4

• up to 40% of ventricular filling.
• sometimes referred to as the “atrial kick.”
• The atrial contribution to ventricular filling varies inversely with duration of ventricular diastole and directly with atrial contractility.

Question 5

Cardiac Cycle - Atrial Contraction (Phase 1)

- After atrial contraction is complete

Answer 5

the atrial pressure begins to fall causing a pressure gradient reversal across the AV valves. This causes the valves to float upward (pre-position) before closure. At this time, the ventricular volumes are maximal, which is termed the end-diastolic volume (EDV).

Question 6

Cardiac Cycle - Isovolumetric Contraction (Phase 2)

Answer 6

• All Valves Closed
• Ventricular depolarization occurs and a rapid increase in intraventricular pressure.
• AV valves to close as intraventricular pressure exceeds atrial pressure
• Ventricular contraction also triggers contraction of the papillary muscles

Question 7

Cardiac Cycle - Isovolumetric Contraction (Phase 2)

- Closure of the AV valves results in

Answer 7

the first heart sound (S1

Question 8

Cardiac Cycle - Isovolumetric Contraction (Phase 2)

- During the time period between the closure of the AV valves and the opening of the aortic and pulmonary valves

Answer 8

• ventricular pressure rises rapidly without a change in ventricular volume (i.e., no ejection occurs)
  
  • Ventricular volume does not change because all valves are closed
  • Contraction, therefore, is said to be “isovolumic” or “isovolumetric.”

Question 9

Cardiac Cycle - Rapid Ejection (Phase 3)

Answer 9

• Aortic and Pulmonic Valves Open; AV Valves Remain Closed
• Rapid ejection of blood into the aorta and pulmonary arteries from the left and right ventricles
• Ejection begins when the intraventricular pressures exceed the pressures within the aorta and pulmonary artery
  
  • causes the aortic and pulmonary valves to open.
• No heart sounds are ordinarily noted during ejection because the opening of healthy valves is silent.
• Blood continues to flow into the atria and the atrial pressures begin to rise, and continue to rise until the AV valves open at the end of phase 5.

Question 10

Cardiac Cycle - Reduced Ejection (Phase 4)

Answer 10

• Aortic and Pulmonic Valves Open; AV Valves Remain Closed
• Approximately 200 msec after the beginning of ventricular contraction, ventricular repolarization occurs
• Repolarization leads to a decline in ventricular tension and therefore the rate of ejection (ventricular emptying) falls.
• Ventricular outward flow still occurs
• Left atrial and right atrial pressures gradually rise due to continued venous return from the lungs and from the systemic circulation, respectively.

Question 11

Cardiac Cycle - Isovolumetric Relaxation (Phase 5)

pt 1

Answer 11

• All Valves Closed
• When the intraventricular pressures falls at the end of phase 4
  
  • aortic and pulmonary valves close causing second heart sound (S2) and the beginning of isovolumetric relaxation.
• After valve closure, the aortic and pulmonary artery pressures rise slighty following by a slow decline in pressure.

Question 12

Cardiac Cycle - Isovolumetric Relaxation (Phase 5)

pt 2

Answer 12

• ventricular volumes remain constant because all valves are closed
  
  • volume of blood that remains in a ventricle is called the end-systolic volume and is ~50 ml in the left ventricle.
• Left atrial pressure (LAP) continues to rise because of venous return from the lungs. The peak LAP at the end of this phase is termed the v-wave.

Question 13

Cardiac Cycle - Rapid Filling (Phase 6)

Answer 13

• A-V Valves Open
• As the ventricles continue to relax at the end of phase 5, the intraventricular pressure will fall below atrial pressures.
  
  • causing AV valves to open and ventricular filling begins
  • ventricular pressures slowly rise as they fill with blood from the atria.
• Ventricular filling is normally silent. When a third heart sound (S3) is audible, it may represent tensing of chordae tendineae and AV ring during ventricular relaxation and filling.This heart sound is normal in children; but is often pathological in adults

Question 14

Cardiac Cycle - Reduced Filling (Phase 7)

Answer 14

• A-V Valves Open
• As the ventricles continue to fill the intraventricular pressures rise
  
  • reduces the pressure gradient across the AV valves so that the rate of filling falls.
• In normal, resting hearts, the ventricle is about 90% filled by the end of this phase.
• Aortic pressure and pulmonary arterial pressures continue to fall during this period.