The Cardiac Cycle Flashcards
what is the cardiac cycle?
all of the events that occur from the beginning of one heart beat to the beginning of the next
what is diastole?
when the ventricles relax and fill with blood
what is systole?
when the ventricles contract and pump blood into the aorta and pulmonary artery
how long are systole and diastole in a heart with a heart rate of 75bpm?
systole = 0.3s diastole = 0.5s
what are the five events that occur during the cardiac cycle?
passive filling atrial contraction isovolumetric contraction ventricular ejection isovolumetric ventricular relaxation
describe the pressure in the heart during passive filling
close to zero
what valves are open during passive filling and what does this allow?
AV valves
ventricles fill
which valves are closed during passive filling?
aortic and pulmonary
how full do the ventricles become during passive filling?
around 80%
what does the P wave on an ECG represent?
atrial depolarisation
where on an ECG does atrial contraction occur?
between the P wave and the QRS complex
what completes the end diastolic volume?
atrial contraction
when does ventricular contraction start on an ECG?
after the QRS
what does the QRS on an ECG signal?
ventricular depolarisation
when do the AV valves shut?
when the ventricular pressure exceeds atrial pressure in isovolumetric ventricular contraction
what produces the first heart sound?
closure of the AV valves
what are the two AV valves?
mitral
tricuspid
what makes isovolumetric ventricular contraction isovolumetric?
all valves are closed so volume doesn’t increase, but pressure does
when does ventricular ejection occur?
when ventricular pressure exceeds the pressure of the aorta and pulmonary artery
what valves open in ventricular ejection?
aortic and pulmonary
what is left in the heart after ventricular ejection?
the end systolic volume
what does the T wave in ECG represent?
ventricular repolarisation
what causes the second heart sound and when does this occur?
when the aortic and pulmonary valves close
when ventricular pressure falls below aortic/pulmonary pressure
what signals the start of isovolumetric ventricular relaxation?
closure of the aortic and pulmonary valves
what signals the start of a new cardiac cycle?
the AV valves opening
