the heart/cardiac cycle

• diastole?

  • atria and ventricles are relaxing
  • blood flows from veins -> atria. recoil of atria walls generates low pressure, allowing more blood flow and atria to fill.
  • pressure builds up allowing AV valves to open. blood flows into ventricles.
• atrial systole?

  • both atria contract, allowing remaining blood flow to force through AV valves into ventricles
• ventricular systole?

  • ventricles contract from apex, increasing pressure and forcing blood upwards into aorta and then pulmonary arteries.
  • changes in pressure force SL valves to open (ventricles increasing) and AV valves to close (atria decreasing).
• define cardiac cycle?

  sequence of events from one heartbeat to the next heartbeat involving systole and diastole