4E- The Cardiac Cycle

what are the two main parts that make up the cardiac cycle

systole (contraction) diastole (relaxation)

what happens during the cardiac cycle

• pressures and volumes change during the cardiac cycle

• atria and ventricles alternately contraction (empty blood) and relax (fill with blood)

  • forces blood from areas of high pressure to areas of lower pressure

• at 75 bpm, one cycle requires 0.8 sec

  • systole and diastole of both atria and both ventricles

what are the 5 phases of the cardiac cycle

1. atrial contraction

2. isometric contraction

3. ventricular ejection

4. isovolumetric relaxation

5. ventricular filling

what happens during atrial contraction

blood goes into ventricle, AV valves open, SL valves close

what happens during isovolumetric contraction

ventricles contract, AV valves close, pressure increases, begins to open SL valves (volume doesn’t change since both valves are closed)

what happens during ventricular ejection

SL valves open, blood. is ejected to pulmonary and systemic circulations

isovolumetric relaxation

all 4 valves closed, atria fill with blood, intraventricular pressure decreases

ventricular filling

pressure in atria increases, AV valves open and ventricles fill

what is end diastolic volume (EDV)

volume in ventricle at end of diastole ~130 ml

what is end systolic volume (ESV)

volume in ventricle at the end of systole, ~60 ml

what is stroke volume

volume ejected per beat from each ventricle ~70 ml

during which part of the cardiac cycle does diastole happen

during atrial contraction

during which part of the cardiac cycle does systole happen

ventricular ejection

what makes the heart sounds you hear during the cardiac cycle

valves opening and closing

during which part of the cardiac cycle is atrial systole, and how long does it last

atrial contraction, 0.1 second

during which part of the cardiac cycle is ventricular systole, and how long does it last

isometric contraction and ventricular ejection, 0.3 sec

during which part of the cardiac cycle is the relaxation period, how long is it, and what happens during it

isometric relaxation and ventricular filling, 0.4 sec, filling

during which part of the cardiac cycle is the P wave

ventricular filling

during which part of the cardiac cycle is the Q wave

atrial contraction

during which part of the cardiac cycle is the R wave

atrial contraction

during which part of the cardiac cycle is the S wave

isovolumetric contraction

during which part of the cardiac cycle is the T wave

ventricular ejection