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Working Mechanism of Human Heart

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Estimated time: 5 minutes
Maharashtra State Board: Class 12

Key Points: Working Mechanism of Human Heart

  • Cardiac Cycle Duration — One complete cardiac cycle = 0.8 sec (Atrial systole + Ventricular systole + Joint diastole).
  • Atrial Systole — SA node generates impulse → atria contract → blood pushed into ventricles (increases flow by ~30%). Impulse travels: SA node → AV node → Bundle of His → Purkinje fibres → ventricles.
  • Ventricular Systole (0.3 sec) — Ventricles contract → cuspid valves close (Lubb sound) → right ventricle pumps deoxygenated blood to pulmonary trunk, left ventricle pumps oxygenated blood to aorta. Atria undergo diastole simultaneously.
  • Ventricular Diastole (0.5 sec) — Ventricles relax → semilunar valves close (Dubb sound) → prevents backflow from pulmonary trunk and aorta.
  • Joint Diastole — All four chambers relax simultaneously for 0.4 sec. This is called complete/joint diastole.
  • Heart Sounds — Lubb = cuspid valves closing (ventricular systole) | Dubb = semilunar valves closing (ventricular diastole).
  • Cardiac Output — Stroke Volume × Heart Rate = 70 × 72 = 5040 mL/min. Regulated by ANS (neural) and adrenaline/acetylcholine (hormonal).

Shaalaa.com | Circulation of Blood in the Heart: Cardiac Cycle

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