3.2.3 The Heart

Question 1

What is the cardiac cycle?

Answer 1

Cardiac cycle is an ongoing sequence of contraction and relaxation of the atria and ventricles that occurs 70 times in each minute when resting.

Question 2

What are the two stages of the cardiac cycle?

Answer 2

• Systole (contracting)
• Diastole (relaxing)

Question 3

How is the direction of the blood flow through the heart maintained?

Answer 3

By pressure changes and the action of valves.

Question 4

What happens to the volume and pressure of the heart when it contracts and why is it beneficial?

Answer 4

The volume decreases and the pressure increases - this helps to push blood through the heart and valves prevent any backflow of the blood.

Question 5

What are the three phases of the cardiac cycle?

Answer 5

• Diastole (muscle relaxed)
• Atrial systole (atrial muscle contracts)
• Ventricular systole (ventricular muscle contracts)

Question 6

Why does the pressure in the aorta never fall to a low level?

Answer 6

Due to the elastic recoil of the artery wall which maintains a pressure even after the blood has passed through.

Question 7

Describe what occurs during Atrial Systole.

Answer 7

• Blood enters atrium. Blood volume increases pressure.
• Atrium pressure is higher than ventricular pressure.
• Forces AV valve open.
• Atrium muscles contract forcing blood into ventricles.

Question 8

Describe what occurs during ventricular systole.

Answer 8

• Blood is forced into ventricle at high pressure.
• Ventricular pressure greater than pressure in atrium.
• Forces AV valves shut.
• Contraction of ventricles causes pressure in ventricles, rises above that of arteries.
• Semi-lunar valves are forced open and blood flows into arteries.

Question 9

Describe what happens during diastole.

Answer 9

• Ventricle pressure lower than aorta/pulmonary artery.
• Semi-lunar valves forced shut.
• Atrium pressure lower than veins and so blood flows into atrium
• Cycle happens again.