cardiac cycle 14A

Question 1

Phase 1- Atrial Contraction

Answer 1

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 2

atrial contraction phase 1 continuation

Answer 2

atrial contraction normally accounts for about 10% of left ventricular filling at rest because most of ventricular filling occurs prior to atrial contraction
-at his heart rates, however the atrial contraction may account for 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 w/ atrial contractility.
After atrial contraction is compete, the atrial pressure begins to fall causing a pressure gradient reversal across the AV valves. this causes the valves to float upward before closure. at this time, the ventricular volumes are maximal which is termed the end-diastolic volume (EDV)

Question 3

Isovolumetric Contraction Phase 2

Answer 3

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 papillary muscles

Question 4

Phase 2 continued

Answer 4

-closure of the av valves results in the first heart sound (S1)
ventricular pressure rises rapidly w/out a change in ventricular volume
- ventricular volume does not change b/c all valves are closed
-contraction therefore is said to be isovolumic

Question 5

Phase 3 Rapid Ejection

Answer 5

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 b/c the opening of healthy valves is silent

Question 6

Phase 4 Reduced Ejection

Answer 6

Aortic and pulmonic valves open; av valves remain closed

• approx 200msec after the beginning of ventricular contraction, ventricular depolarization occurs
• repolarization lead to a decline in ventricular tension and therefore the rate of ejection(ventricular emptying) falls.
• left atrial and right atrial pressures gradually rise due to continued venous return from the lungs and from the systemic circulation, respectively.

Question 7

Phase 5 Isovolumetric Relaxation

Answer 7

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 pressure rise slightly following by a slow decline in pressure
• -volume of blood that remains in a ventricle is called the end-systolic volume and is about 50ml in the left ventricle
• left atrial pressure (LAP) continues to rise b/c of venous return from the lungs. the peak LAP at the end of this phase is termed the v-wave

Question 8

Phase 6 Rapid filling

Answer 8

AV VALVLES OPEN

• as the ventricles continue to relax at the end of phase 5 the intraventriuclar press 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 renting of chord tenineae and av ring during ventricular relaxation and filling. this heart sound is normal in children; but is often pathological in adults

Question 9

Phase 7 reduced filling

Answer 9

AV VALVES OPEN

• as the ventricles continue to fill the intraventricular pressure rise
• -reduces the press gradient across the av valves so that the rate of filling falls
• IN NORMAL, RESITNG 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