CIE A Level Biology复习笔记8.3.3 The Cardiac Cycle

• The contraction of the heart is called systole, while the relaxation of the heart is called diastole
• Atrial systole is the period when the atria are contracting and ventricular systole is when the ventricles are contracting
• Ventricular systole happens around 0.13 seconds after atrial systole
• During ventricular systole, blood is forced out of the pulmonary artery (to the lungs) and aorta (to the rest of the body)
• One systole and diastole makes a heartbeat and lasts around 0.8 seconds in humans. This is the cardiac cycle

Pressure changes

• During systole and diastole, heart valves open and close as a result of pressure changes
• Valves are an important mechanism to stop blood flowing backwards
• During diastole, the heart is relaxing
  • The atrioventricular valves open and the semilunar valves are closed
• During systole, the heart contracts and pushes blood out of the heart
  • During this time, the atrioventricular valves are closed and the semilunar valves are open

Pressure Changes in the Heart Table