The Cardiac Cycle Flashcards
What is the cardiac cycle?
The sequence of events in one heartbeat, repeated around 70 times per minute at rest
What are the two main phases of the cardia cycle?
- Systole - contraction of the heart
- Diastole - relaxation of the heart
What happens during diastole (relaxation of the heart)?
1/ Blood returns to the atria via the pulmonary vein (from the lungs) and vena cava (from the body)
2/As the atria fill, their pressure increases
3/ When atrial pressure exceeds ventricular pressure, atrioventricular valves open, allowing blood to pass into the ventricles (aided by gravity)
4/The atria and ventricles are both relaxed at this point
What causes the atrioventricular valves to open during diastole?
When the pressure in the atria exceeds the pressure in the ventricles
What happens to the ventricles during diastole?
Ventricular walls relax and recoil, lowering the pressure in the ventricles
The ventricular pressure becomes lower than that in the aorta and pulmonary artery
What causes the semi - lunar valves to close during diastole?
The lower pressure in the ventricles compared to the aorta and pulmonary artery causes the semi - lunar valves to close
What sound is produced when the semi - lunar valves close?
The “dub” sound of the heartbeat
What happens during atrial systole?
The atria contract, forcing the remaining blood into the ventricles
How does blood move from the atria to the ventricles during atrial systole?
Atrial walls contract, increasing the pressure and the ventricular walls recoil, helping blood flow into the ventricles
What is the state of the ventricles during atrial systole?
The ventricular walls remain relaxed
What role does the recoil of the ventricles play in the atrial systole?
The recoil of the relaxed ventricle walls helps draw blood from the atria into the ventricles
What sound is produced when the atrioventricular valves close?
The ‘lub’ sound of the heartbeat
What happens during ventricular systole?
Ventricles contract simultaneously after a short delay. Blood pressure then increases in the ventricles. Leading to the atrioventricular valves closing to prevent backflow into the atria
Why is there a short delay before ventricular systole begins?
To allow the ventricles to fill completely with blood before contracting
What causes the atrioventricular valves close during ventricular systole?
The increase in pressure within the ventricles as they contract forces the atrioventricular valves shut, preventing backflow into the atria
When do the semi - lunar valves open during ventricular systole?
When ventricular pressure exceeds the pressure in the aorta and pulmonary artery, forcing blood into these vessels
Why do the ventricles have thick muscular walls?
To contract forcefully, generating high pressure needed to pump blood around the body
Why is the left ventricle thicker than the right ventricle?
The left ventricle pumps blood to the entire body, so requiring higher pressure. The right ventricle inly pumps blood to the lungs, so it has a relatively thinner wall
