the cardiac cycle Flashcards
normally heart valves produce a sound when they
shut, not when they open
the cardaic cycle refers to
all events that occur from the beginning of one heart beat to the beginning of the next
diastole
the heart ventricles are relaxed and fill with blood
systole
the heart ventricle contracts and pumps blood into the aorta and pulmonary artery
events during the cardiac cycle
passive filling atrial contraction isovolumetric ventricular contraction ventricular ejection isovolumetric ventricular relaxation
what happens during passive filling
pressure in atria and ventricles is close to 0
AV valves open so venous return flows into ventricles
same events happen in the right side of the heart but the pressures are much lower
ventricles become 80% full by passive filling
what happens during atrial contraction
the P wave in the ECG signals atrial depolarisation
the atria contracts between the P wave and the QRS
atrial contraction complete the END DIASTOLIC VOLUME the end diastolic pressure is a few mmHg
what happens during isovolumetric ventricular contraction
ventricular contraction starts after the QRS in the ECG
ventricular pressure rises
when sufficient pressure is reached, the AV valves shut
this produces the first heart sound (LUB)
the aortic valve is still shut so no blood can enter or leave the ventricle
the tension rises around a closed volume “isovolumetric contraction”
the ventricular pressure rises very steeply
what happens during ventricular ejection
when the venticular pressure exceeds aorta/pulmonary artery pressure the aortic/pulmonary valve opens - this is silent
stroke volume is ejected by each ventricle, leaving behind the end systolic volume
aortic pressure rises
what happens next in ventricular ejection…
the T wave in the ECG signals ventricular repolarisation
the ventricles relax and the ventricular pressure falls
when the pressure gets too low the valves shut
this produces the second heart sound (DUB)
the valve vibration produces the dicrotic notch in aortic pressure curve
isovolumetric ventricular relaxation
closure of aortic/pulmonary valves signals the start of isovolumetric ventricular relaxation
the tension falls
when the ventricular pressure falls below atrial pressure, AV valves open and the heart starts a new cycle
what is the first heart sound caused from
closure of mitral and tricuspid valves
it sounds like lub
the first heart sound marks the beginning of
systole
the second heart sound is caused from
closure of aortic and pulmonary valves
it sounds like dub
the second heart sound marks the
end of systole and the beginning of diastole
the jugular venous pulse
occurs right after atrial pressure waves
