Cardiac cycle

Question 1

In which stage(s) are the ventricles relaxed?

Answer 1

1 and 3

Question 2

Explain stage 1.

Answer 2

The ventricles are relaxed.

The atria contract. This decreases the volume of the chambers and increases the pressure inside the chambers.

This pushes blood out of the ventricles.

Question 3

Explain stage 2.

Answer 3

The atria relax.

The ventricles contract. This decreases the volume and increases the pressure.

Their pressure is higher in the ventricles than the atria, which forces the AV valves shut.

The pressure in the ventricles is higher than in the aorta and pulmonary artery, which forces the SL valves open and blood is forced out into these arteries.

Question 4

Explain stage 3.

Answer 4

The ventricles and atria relax.

Higher pressure in the vena cava and pulmonary vein means that blood returns to the heart.

In turn, this starts to increase the pressure in the atria.

As the ventricles continue to relax, their pressure falls below that of the atria, so the AV valve open. This allows blood to flow passively into the ventricles from the atria.

Question 5

In which stage(s) does the atria contract?

Answer 5

Stage 1

Question 6

In which stage(s) does the atria relax?

Answer 6

Stage 2 and 3.

Question 7

In which stage(s) do the ventricles contract?

Answer 7

Stage 2

Question 8

In stage 1, the atria contract. What does this result in?

Answer 8

This decreases the volume of the chambers and increases the pressure inside the chamber.

This pushes blood into the ventricles.

Question 9

In stage 2, the ventricles contract. What does this do?

Answer 9

This increases the pressure of the ventricles.
The pressure becomes higher in the ventricles than in the atria, which forces the AV valve to close and prevent backflow.

The pressure is also higher than in the aorta and pulmonary artery, which forces open the semilunar valves and blood is forced out into these arteries.

Question 10

In stage 3, the atria and ventricles are relaxed. What does this do?

Answer 10

The higher pressure in the pulmonary artery and aorta closes the SL valves to prevent back flow into the ventricles.

Blood then flows into the heart and the atria fill again due to the higher pressure in the vena cava and pulmonary vein.
In turn this increases the volume of the atria.

As ventricles continue to relax, their pressure falls below the pressure of the atria so the AV valves open.

This allows blood to flow passively into the ventricles from the atria.

The atria then contracts and the process begins again.