Understanding the Cardiac Cycle

Oct 14, 2024

Mindmap

Cardiac Conducting System and Cardiac Cycle

Overview

  • The cardiac conducting system generates and spreads electrical impulses to signal cardiac contractile cells to contract.
  • The heart must contract and relax in a coordinated manner to push blood properly through the heart and the body.
  • Cardiac Cycle: Period between the start of one heartbeat and the beginning of the next.
    • Involves contraction (systole) and relaxation (diastole) of heart chambers.

Phases of the Cardiac Cycle

  1. Atrial Systole (Atrial Contraction)

    • Blood is already present in both the atria and ventricles.
    • Atria contract, forcing additional blood into the ventricles through atrioventricular (AV) valves.
    • Ventricles are filled with maximum blood.

  2. Atrial Diastole (Atrial Relaxation)

    • Atria relax and begin to expand.
    • AV valves close to prevent backflow of blood into the atria from ventricles.

  3. Ventricular Systole (Ventricular Contraction)

    • Ventricles begin contracting, increasing blood pressure inside.
    • AV valves remain shut to prevent backflow into the atria.
    • Initial contraction is isovolumetric (no change in blood volume as all valves are closed).
    • Pressure eventually forces open semilunar valves, ejecting blood into pulmonary trunk or aorta.
    • Stroke Volume: Amount of blood ejected from the ventricles.
    • End Systolic Volume (ESV): Blood left in ventricles after contraction.

  4. Ventricular Diastole (Ventricular Relaxation)

    • Ventricles relax, pressure drops.
    • Semilunar valves close to prevent backflow into ventricles.
    • Initially, AV valves remain closed.
    • Isovolumetric relaxation occurs (no change in blood volume).
    • Pressure in atria eventually exceeds that in ventricles, opening AV valves.
    • Blood flows passively from atria to ventricles.

Key Terms

  • End Diastolic Volume (EDV): Maximum blood volume in ventricles at end of diastole.
  • Isovolumetric Contraction: Ventricles contract with no change in blood volume.
  • Isovolumetric Relaxation: Ventricles relax with no change in blood volume.

Summary

  • The cardiac cycle consists of a series of coordinated contractions and relaxations: atrial systole, atrial diastole, ventricular systole, and ventricular diastole.
  • Blood flows through the heart in a specific sequence, regulated by pressure changes and valve operations, ensuring efficient circulation.