3B - The cardiac cycle

Question 1

What do Atrioventricular valves do ?

Answer 1

Link the atria to the ventricles and stop blood flowing back into atria when ventricles contract

Question 2

What do semi-lunar valves do ?

Answer 2

Link ventricles to pulmonary artery and aorta and stop blood flowing back into heart after ventricles contract

Question 3

When do valves open ?

Answer 3

When the blood pressure above the valve is higher than the blood pressure below the valve

Question 4

What happens during atrial systole (contraction)?

Answer 4

• Ventricles relax
• Both atria contract, decreasing volume of atria and increasing pressure
• Higher pressure in atria keeps AV valves open
• Blood flows into ventricles to fill them completely
• SL valves in vena cava and pulmonary arteries shut

Question 5

What happens during ventricular systole ?

Answer 5

• Atria relax
• Both ventricles contract
• Increases pressure in ventricles which closes AV valves
• Opens aortic and pulmonary SL valves so blood flows into pulmonary artery and aorta

Question 6

What happens during diastole ?

Answer 6

• Ventricles and atria relax
• This increases volume and lowers pressure in chambers
• Greater pressure in pulmonary artery and aorta closes SL valves to prevent back flow
• Atria fill with blood due to higher pressure in the pulmonary veins and vena cava
• Ventricles also passively fill as AV valves open

Question 7

What is the equation for cardiac output ?

Answer 7

Cardiac output = stroke volume x heart rate

Question 8

What is the sequence of the cardiac cycle ?

Answer 8

1. Cardiac diastole
2. Atrial systole, ventricular diastole
3. Atrial diastole, ventricular systole