Physiology 3- The Cardiac Cycle

Question 1

What is the cardiac cycle?

Answer 1

All of the events which occur from the beginning of one heartbeat to the beginning of the next

Question 2

What happens in diastole?

Answer 2

The heart ventricles are relaxed and fill with blood

Question 3

What happens in systole?

Answer 3

The heart ventricles contract and pump blood into the aorta and pulmonary artery

Question 4

Which is longer, diastole or systole?

Answer 4

Diastole

Question 5

At the end of diastole, which valves are open and which are closed?

Answer 5

AV valves open

Aortic and pulmonary valves are closed

Question 6

What are the 5 phases of the cardiac cycle?

Answer 6

Passive filling, atrial contraction, isovolumetric ventricular contraction, ventricular ejection, isovolumetric ventricular repolarisation

Question 7

What happens in passive filling?

Answer 7

Heart chambers are very low pressure. AV valves are open and so blood flows from atria to ventricles

Question 8

How much filling takes place during passive filling?

Answer 8

80%

Question 9

What happens in atrial contraction?

Answer 9

Atria contract and the last of the blood is squeezed into the ventricles to complete EDV

Question 10

What does the p wave represent on an ECG?

Answer 10

Atrial depolarisation

Question 11

Where does atrial contraction correlate to on an ECG?

Answer 11

Between the p wave and QRS complex

Question 12

What happens in isovolumetric ventricular contraction?

Answer 12

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.

Question 13

Where does isovolumetric ventricular contraction take place on an ECG?

Answer 13

After the QRS complex

Question 14

What happens in ventricular ejection?

Answer 14

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’

Question 15

What does the t wave signal on an ECG?

Answer 15

Ventricular repolarisation

Question 16

What happens in isovolumetric ventricular repolarisation?

Answer 16

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

Question 17

What does the 1st heart sound signify?

Answer 17

The beginning of systole

Question 18

What does the 2nd heart sound signify?

Answer 18

The beginning of diastole

Question 19

Why does atrial pressure not fall to 0 during diastole?

Answer 19

Elastic properties of the heart and the great vessels stretching and recoiling

Question 20

Where will pressure changes in the RA be able to be seen and why?

Answer 20

Internal jugular vein because there are no valves between the two

Question 21

What does the a wave of JVP mean?

Answer 21

Atrial contraction

Question 22

What does the c wave of JVP mean?

Answer 22

Bulging of tricuspid valve into atrium during ventricular contraction

Question 23

What does the v wave of JVP mean?

Answer 23

Rise of atrial pressure during atrial filling