The Cardiac Cycle

Question 1

What are the 2 types of valves in the heart and their functions?

Answer 1

Atriaventricular: stops blood flowing back into the atria when ventricles contract
Cords attach to the ventricles to stop them being forced upwards
Semilunar: Links ventricles to arteries
Stops blood flowing back into the ventricles when they contract

Question 2

How do valves involve a unidirectional flow?

Answer 2

If pressure is greater behind the valve, they open
If pressure is greater in front of the valve, they close

Question 3

What is the cardiac cycle and its 3 stages?

Answer 3

Ongoing sequence of contraction and relaxation of the atria and ventricles that keeps blood continuously circling around the body (0.8s)
3 stages:
- Atrial systole
- Ventricular systole
- Diastole

Question 4

What happens in atrial systole?

Answer 4

• Walls of atria contract
• Atrial volume reduces, atrial pressure increases
• Pressure in atria is greater than pressure of the ventricles
• So AV valves are forced open and blood is pushed into ventricles

Question 5

What happens in ventricular systole?

Answer 5

• Atria relaxes
• Walls of ventricles contract
• Volume of ventricles reduces and ventricular pressure increases
• Ventricular pressure rises above pressure of atria and AV valves are forced shut to prevent backflow
• Once ventricular pressure is greater than aorta and pulmonary artery pressure, the SL valves are forced open
• Blood is forced out the heart

Question 6

What happens in diastole?

Answer 6

• Both atria and ventricles relax
• SL valves are forced shut by pressure of aorta and pulmonary artery
• Blood begins to fill atria as pressure is less than vena cavas and pulmonary vein
• Some blood enters passively into ventricles