Physiology 3- The Cardiac Cycle Flashcards
What is the cardiac cycle?
All of the events which occur from the beginning of one heartbeat to the beginning of the next
What happens in diastole?
The heart ventricles are relaxed and fill with blood
What happens in systole?
The heart ventricles contract and pump blood into the aorta and pulmonary artery
Which is longer, diastole or systole?
Diastole
At the end of diastole, which valves are open and which are closed?
AV valves open
Aortic and pulmonary valves are closed
What are the 5 phases of the cardiac cycle?
Passive filling, atrial contraction, isovolumetric ventricular contraction, ventricular ejection, isovolumetric ventricular repolarisation
What happens in passive filling?
Heart chambers are very low pressure. AV valves are open and so blood flows from atria to ventricles
How much filling takes place during passive filling?
80%
What happens in atrial contraction?
Atria contract and the last of the blood is squeezed into the ventricles to complete EDV
What does the p wave represent on an ECG?
Atrial depolarisation
Where does atrial contraction correlate to on an ECG?
Between the p wave and QRS complex
What happens in isovolumetric ventricular contraction?
Ventricular pressure rises until it becomes ore than in the atria. This then causes the AV valves to close and cause the 1st heart sound ‘lub’. The aortic/pulmonary valves are still shut so ventricular pressure rises steeply.
Where does isovolumetric ventricular contraction take place on an ECG?
After the QRS complex
What happens in ventricular ejection?
When the pressure in the ventricles exceeds the pressure in the vessels, this causes the aortic/pulmonary valves to open and the stroke volume is ejected. This leaves behind the end systolic volume. The pressure in the vessels then increases and when this becomes higher than ventricles the aortic/pulmonary valves shut which causes the second heart sound ‘dub’
What does the t wave signal on an ECG?
Ventricular repolarisation
What happens in isovolumetric ventricular repolarisation?
Signalled by the closure of the aortic/pulmonary valves- the ventricle is again a closed box. When the tension falls there is ventricular relaxation and when this falls below atrial pressure it causes the AV valves to open again and a new cycle starts
What does the 1st heart sound signify?
The beginning of systole
What does the 2nd heart sound signify?
The beginning of diastole
Why does atrial pressure not fall to 0 during diastole?
Elastic properties of the heart and the great vessels stretching and recoiling
Where will pressure changes in the RA be able to be seen and why?
Internal jugular vein because there are no valves between the two
What does the a wave of JVP mean?
Atrial contraction
What does the c wave of JVP mean?
Bulging of tricuspid valve into atrium during ventricular contraction
What does the v wave of JVP mean?
Rise of atrial pressure during atrial filling
