The cardiac cycle 3.2.5

Question 1

How long is the cardiac cycle?

Answer 1

One complete sequence of the heart filling and pumping blood (heartbeat) which takes approx 0.8 seconds

Question 2

Define systole

Answer 2

When the cardiac muscle contracts (left ventricle) and the heart pumps blood out through the aorta and pulmonary arteries

Question 3

Define diastole

Answer 3

Cardiac muscle relaxes (left ventricle) and the heart fills with blood.

Question 4

What is an atrial systole?

Answer 4

The atria contract and force blood into the ventricles

Question 5

What is a ventricular systole?

Answer 5

Ventricles contract and force blood into the arteries

Question 6

What causes the ‘lub dub’ sound?

Answer 6

The closing of the valves (not the contraction of the heart muscle)

Question 7

State the functions that occur during atrial systole

Answer 7

• Muscles of the atria contract and the pressure in these increase
• The semi lunar valves in the vena cava and pulmonary vein close
• The atrioventricular valves open, allowing blood into the ventricles
• Pressure decreases
• 0.1 seconds

Question 8

State the functions that occur during ventricular systole

Answer 8

• Muscles of the ventricles contract and pressure increases
• Atrioventricular valves close
• The semi lunar valves in the aorta and pulmonary arteries open
• Pressure decreases
• 0.3 seconds

Question 9

State the functions that occur during diastole

Answer 9

• Pressure in the ventricles decreases
• Semi lunar valves in the aorta and pulmonary arteries close
• Heart muscles relax
• Blood flows into the atria from the vena cava and pulmonary vein
• Blood pressure remains low inside the atria and ventricles

Question 10

What do the valves do?

Answer 10

Prevent back flow in the heart

Question 11

What are valves controlled by?

Answer 11

By pressure changes in the heart chambers.
High pressure behind the valve forces it to open
- High pressure infront of the valve closes it

Question 12

How do the elastic fibres in the artery walls help to maintain pressure?

Answer 12

The elastic recoil in the walls helps to maintain a high pressure as it keeps blood pumping throughout the body.

Question 13

Define cardiac output

Answer 13

The volume of blood pumped from the left ventricle per minute.

Question 14

What two factors does cardiac output depend on?

Answer 14

Stroke volume and heart rate