Cardiac Cycle Flashcards
Cardiac cycle
One completed cycle of contraction & relaxation of all 4 chambers of the heart
What are the events of the cardiac cycle?
- Ventricular filling
- Heart contraction
- Ejection of blood from ventricle into the circulation
- Heart relaxation
- …the cycle continues…
Systole
Contraction
Dystole
Relaxation
Does the heart spend more time in diastole or systole?
Diastole
Describe blood flow through the right side of the heart.
Pulmonary Circulation
- Right atrium receives deoxygenated blood from the body (via the superior and inferior vena cava)
- Blood passes through the right tricuspid valve into the right ventricle
- Then passes through the pulmonary valve into the pulmonary artery
Destination – lungs
Describe blood flow through the left side of the heart.
Systemic circulation
- Left atrium receives oxygenated blood from the lungs (via the pulmonary veins)
- Blood then passes through mitral valve into the left ventricle
- Though the aortic valve into the aorta
Destination – the body
Cardiac cycle.
Mechanical events which occur with the flow of blood through the heart in one heartbeat
Describe the cardiac cycle & blood flow.
- Vena Cava (deoxygenated blood)
- Right Atrium
- Right Ventricle (via Tricuspid valve)
- Pulmonary arteries (via semilunar valves)
- Lungs
- Pulmonary veins (Oxygenated blood)
- Left Atrium
- Left Ventricle (via Bicuspid valve)
- Rest of the body
…Repeat…
Early diastole.
- Whole heart relaxed
- Pulmonary and aortic valves shut
- AV valves (tricuspid and bicuspid/mitral) open
- Blood flowing passively from great veins through atria to ventricles
Atrial systole.
- Atria contract forcing blood into the ventricles
- Atria then relax
Ventricular systole: isovolumetric contraction.
- Ventricles contract
- Increase ventricular pressure
- AV valves now close
- Aortic and pulmonary valves still closed – this contraction does not bring about any change in volume
Ventricular systole: ventricular ejection.
- Ventricular pressure continues to rise
- Aortic and pulmonary valves forced open
- Blood rapidly ejected into the aorta (L) and pulmonary artery (R)
Ventricular diastole: isovolumetric relaxation.
- Ventricles relax and ventricular pressure drops
- Blood in aorta and pulmonary artery starts to flow back towards heart = aortic and pulmonary valves shut
What does the atrioventricular node cause?
- Slows impulse down
- Allows time for atrial contraction + ventricular filling
What is the primary function of the sinoatrial (SA) node in the heart?
To act as the pacemaker of the heart
What is the primary purpose of coronary arteries?
To supply oxygenated blood to the myocardium
What does the sinoatrial node cause?
Depolarisation + contraction of both atria (atrial systole)
Why do heart valves open & close?
Pressure differences
