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Cardiovascular | Cardiac Cycle

Ninja Nerd・21 minutes read

The cardiac cycle involves the flow of blood through the heart's chambers based on pressure differentials and valve openings and closings, crucial for proper functioning. Ventricular contractions and pressure changes lead to the opening and closing of valves, allowing blood to move in and out of the heart efficiently.

Insights

  • The cardiac cycle involves a complex series of events where blood flows through the heart's chambers, regulated by differences in pressure and valve mechanisms.
  • The opening and closing of AV and semilunar valves are crucial determinants of blood flow direction within the heart, with pressure differentials playing a key role in orchestrating these movements.

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Recent questions

  • What is the average duration of the cardiac cycle?

    0.8 seconds

  • What causes the first heart sound "Lub"?

    AV valves closing

  • What initiates atrial depolarization in the heart?

    SA node firing

  • What determines the opening and closing of heart valves?

    Pressure differences in ventricles and arteries

  • What phase of the cardiac cycle focuses on blood ejection from the ventricles?

    Mid to late ventricular systole

Related videos

Summary

00:00

Cardiac Cycle Mechanics and Pressure Dynamics

  • The cardiac cycle involves mechanical events where blood flows through the heart's chambers, taking about 0.8 seconds on average.
  • Discussion includes differences in atrial versus ventricle pressure, AV valves, and semilunar valves (pulmonary and aortic).
  • During mid to late ventricular diastole, blood returns to the heart from various veins, opening AV valves for passive blood flow into the ventricles.
  • Atrial pressure exceeds ventricular pressure, causing AV valves to open, allowing passive blood flow into the ventricles.
  • Ventricular pressure remains lower than arterial pressure, keeping semilunar valves closed to prevent blood backflow.
  • The SA node firing leads to atrial depolarization, seen as a P wave on an EKG, marking the period of ventricular filling.
  • Isovolumetric contraction phase begins as ventricles contract, pushing blood upwards, with semilunar valves closed due to lower ventricular pressure.
  • AV valves close as ventricular pressure surpasses atrial pressure, leading to the first heart sound "Lub" during isovolumetric contraction.
  • Ventricular pressure eventually exceeds arterial pressure, causing semilunar valves to open, allowing blood ejection from the ventricles.
  • The difference in pressures between ventricles and arteries determines valve opening and closing, crucial in the cardiac cycle's functioning.

13:21

Heart Cycle: Blood Flow and Pressure Dynamics

  • Blood moves from areas of high pressure to areas of low pressure in the heart.
  • Ventricles contract, causing pressure to rise and valves to open, allowing blood to move out.
  • The phase focuses on maintaining a visible flow throughout all phases of the heart cycle.
  • Ventricles eject blood as their pressure exceeds that of the pulmonary trunk and aorta.
  • Semilunar valves open as blood is pushed out by the ventricles.
  • AV valves remain closed due to greater pressure in the ventricles compared to the atria.
  • This phase is known as mid to late ventricular systole or ventricular ejection phase.
  • Aortic and pulmonary trunk pressure rises as blood is distributed to various circuits, causing semilunar valves to close.
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