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Understanding Heart Valves and Cardiac Cycle

Sep 30, 2024

Anatomy and Function of the Heart Valves

Overview

  • The heart consists of four chambers:
    • Right atrium
    • Right ventricle
    • Left atrium
    • Left ventricle
  • Valves ensure one-way blood flow through the heart:
    • Atrioventricular (AV) valves: Between atria and ventricles
      • Right side: Tricuspid valve
      • Left side: Mitral (bicuspid) valve
    • Semilunar valves:
      • Right side: Pulmonary valve
      • Left side: Aortic valve

Function of Valves

  • Valves open and close based on pressure differences:
    • Pressure behind the valve causes it to open.
    • When pressure changes, the valve closes to prevent backflow.
  • Chordae tendineae: Tendon-like cords attached to AV valve leaflets, preventing valve prolapse during ventricular contraction.

Cardiac Cycle

Overview

The cardiac cycle refers to the events in the heart during a single heartbeat, involving contraction and relaxation phases.

Phases of the Cardiac Cycle

  1. Ventricular Filling

    • Atrial pressure > Ventricular pressure
    • AV valves open, allowing blood to flow from atria to ventricles
    • Initial rapid filling phase followed by diastasis (slower filling)
    • Atria contract toward the end of filling (P-wave), adding more blood to ventricles

  2. Isovolumetric Ventricular Contraction

    • Ventricles depolarize and begin to contract
    • Ventricular pressure > Atrial pressure
    • AV valves close, producing the first heart sound
    • No volume change; all valves closed

  3. Ventricular Ejection

    • Ventricular pressure > Aortic pressure
    • Aortic valve opens, blood is ejected from ventricle
    • AV valve remains closed
    • Initial rapid ejection slows due to inertia

  4. Isovolumetric Ventricular Relaxation

    • Ventricular pressure < Aortic pressure
    • Aortic valve closes, producing the second heart sound
    • No volume change; all valves closed
    • Ventricular pressure decreases until it is less than atrial pressure

Definitions of Cardiac Cycle Phases

  • Systole: Ventricular muscle contraction phase
    • Includes isovolumetric contraction and ventricular ejection
  • Diastole: Ventricular muscle relaxation phase
    • Includes isovolumetric relaxation and ventricular filling
  • Terms like "systole" and "diastole" generally refer to the ventricles unless specified for atria (e.g., atrial systole).

These notes highlight the function and mechanism of heart valves and detail the cardiac cycle with its distinct phases and the corresponding physiological events.

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