Lecture 12: The Cardiac Cycle

Question 1

When are the atrioventricular valves open and closed? (in terms of pressure)

Answer 1

AV valves are open when the Pressure of the atria > Pressure of the ventricles

AV valves are closed when the Pressure of the ventricles > Pressure of the atria

Question 2

When are the semilunar valves open and closed? (in terms of pressure)

Answer 2

Semilunar valves are open when the Pressure of the ventricles > Pressure of the aorta/pulmonary artery

AV valves are closed when the Pressure of the aorta/pulmonary artery > Pressure of the ventricles

Question 3

How does the aorta act as a pressure reservoir?

Answer 3

flow into aorta > flow out out aorta/runoff

During systole, the excess blood that cannot be accommodated by the aorta is kept there due to the elasticity of the walls. It stretches out in order to maintain the flow.

During diastole, the walls recoil

Question 4

How does the resistance in the pulmonary circulation compare to that of the systemic circulation?

Answer 4

Q=ΔP/R

Flow must be kept the same.
However, pressure is lower in the pulmonary circulation.
Therefore, the resistance also has to be lower in pulmonary circulation (right side of heart).

Question 5

How long does each phase of the cardiac cycle last?

Answer 5

Ventricular diastole = 0.5 sec (~2/3rds)
Ventricular systole = 0.3 sec (~1/3rd)

Total heartbeat duration= 0.8 sec