Cardiac Cycle

Question 1

What occurs in phase 1 of the cardiac cycle?

Answer 1

Ventricular filling:

1. Blood flows passively into the left ventricle from the left atrium through the mitral valve
2. Blood in left ventricle is at end diastolic volume

Question 2

What occurs in phase 2 of the cardiac cycle?

Answer 2

Ventricular systole:

1. Ventricles contract (isovolumetric contraction)
2. Left ventricle pressure rises rapidly, closing mitral valve
3. When left ventricle pressure exceeds aortic pressure, semi-lunar valve opens
4. Blood enters aorta

Question 3

What occurs in phase 3 of the cardiac cycle?

Answer 3

Ventricular diastole:

1. As left ventricle stops contracting, pressure falls rapidly
2. Aortic and pulmonary valves close.
3. Brief rise in aortic pressure - dicrotic notch

Question 4

How long does ventricular systole last?

Answer 4

0.3 seconds

Question 5

How long does ventricular diastole last?

Answer 5

0.5 seconds

Question 6

Describe Frank-Starling Law.

Answer 6

‘Stroke volume will increase in response to an increased end diastolic volume when all other factors remain constant’

As a larger volume of blood flows into the ventricles, blood stretches the wall of the heart (during diastole). This increases the force of contraction and thus quantity of blood pumped into the aorta (during systole).