AS EDEXCEL BIOLOGY UNIT 1 NOTES - CARDIAC CYCLE & HEART RATE

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THE CARDIAC CYCLE: an ongoing sequence of contraction (systole) and relaxation (diastole) of the atria and ventricles that keeps blood continuously circulating around the body.

1. VENTRICULAR DIASTOLE, ATRIAL SYSTOLE.

  • Ventricles relaxed. Atria contracts, increasing pressure inside the chamber. Blood is pushed into the ventricles.
  • Slight increase in ventricular pressure as they received blood from contracting atria.

2. VENTRICULAR SYSTOLE, ATRIAL DIASTOLE.

  • Atria relaxes, and ventricles contract: this increases pressure.
  • Pressure becomes higher in ventricles than atria - AV valves shut to prevent back-flow.
  • Pressure also higher than in aorta and pulmonary artery. SL valves open, and blood is pushed out.

3. VENTRICULAR DIASTOLE, ATRIAL DIASTOLE.

  • Ventricles and atria relax. High pressure in aorta and pulmonary artery closes SV valves to prevent back-flow. Blood returns to heart and atria fill due to

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