As atria contract, rising atrial pressures push blood into the ventricles thru the open right and left AV valves.
STEP 2 - Atrial Systole
Start of atrial systole, ventricles already filled 70%. As atria contract, rising atrial pressure provide the remaining 30 percent by pushing blood thru the open AV valves. Atrial systole 'tops off' ventricles.
STEP 3 - Atrial Systole
End of atrial systole, each ventricle contains maximum amount of blood that it will hold in cardiac cycle = End diastolic volume EDV
STEP 4 - Ventricular Systole.
ventricles are contracting. bloow flow has yet to occur. ventricles contract isometrically: generate tension and pressure. flow does not occur. isovolumetric contraction: all valves closed. volume constant and pressure rises.
STEP 5 - Ventricular Systole
Once ventricle pressure exceeds that in arterial trunks. semilunar valves open and blood flows into pulmonary and aortic trunks = ventricular ejection. isotonically contract: muscle cells shorten. tension constant.
STEP 6 - Ventricular Systole
near end of VS, ventricular pressure falls.blood in aorta + pulmonary trunk now starts to flow twrd ventricles-> closes semilunar valves. pressure rises again as arterial walls recoil, amt of blood remaining in ventricle = end systolic volume
STEP 7 - Ventricular Diastole
all heart valves closed.vent. myocardium relaxing vent pressures higher than atrial pressures blood cannot flow into ventricles. isovolumetric relaxation; rapid drop in pressure over this period
STEP 8 - Ventricular Diastole
when ventricular pressure fall below atria. atrial pressure forces valves open.blood flows into ventricles. both atria + vent = diatole. vent. pressure continues to fall > chambers expand.
