cardiac heart cycle 2_14

Blood Circulation Overview

  • Blood Circulation Pathways

    • Blood is pumped from the heart to different parts of the body through two main circuits:

      • Systemic Circuit:

        • Blood leaves the left side of the heart.

        • Begins at the aorta and branches out into major arteries that supply the body's tissues, excluding the lungs.

        • Blood reaches capillary beds where gas, nutrients, and waste exchange occurs in body tissues (skeletal muscle, glands, gut).

        • Returns through veins to the vena cava, re-entering the heart's right side.

      • Pulmonary Circuit:

        • Blood leaves the right side of the heart.

        • Heads towards the lungs through the pulmonary trunk for gas exchange (O2 and CO2) in the pulmonary capillary beds.

Heart Anatomy and Blood Flow

  • Unidirectional Blood Flow:

    • Blood flow through the heart is unidirectional due to heart valves.

    • Comprises:

      • Atrioventricular (AV) Valves: separate atria from ventricles (right AV valve and left AV valve).

      • Semilunar Valves: located at the exits of the ventricles (pulmonary and aortic valves).

    • Valves ensure one-way flow, preventing backflow.

Heart Valves Structure

  • Valve Anatomy:

    • Composed of flaps (also called leaflets) that open and close to regulate blood flow.

    • Connected to the heart wall via chordae tendineae (cord-like tendons) and papillary muscles (muscle projections from the heart wall).

      • Chordae tendineae prevent flaps from inverting when ventricles contract.

Cardiac Cycle and Pressure Dynamics

  • Cardiac Cycle Phases:

    • Atrial Contraction:

      • Increases pressure in the atria, opening AV valves, allowing blood flow into ventricles.

    • Ventricular Contraction:

      • Initiated by the QRS complex on an EKG.

      • Increases ventricular pressure, which causes blood to be ejected into the aorta.

      • As pressure rises above atrial pressure, AV valves close (S1 heart sound).

      • Ventricles eject blood until pressures equalize with the aorta.

    • Ventricular Relaxation:

      • Reduces pressure in the ventricles, allowing AV valves to open when atrial pressure exceeds ventricular pressure.

      • Blood flows passively into ventricles during relaxation.

Sounds of the Heart

  • Heart Sounds:

    • S1 (Lub): Sound made when AV valves close during ventricular contraction.

    • S2 (Dub): Sound made when semilunar valves close after blood ejection.

    • Murmurs indicate abnormal sounds due to backflow or structural issues with heart valves.

Blood Pressure Changes and Heart Function

  • Electrical and Pressure Changes:

    • Blood flow is driven by pressure gradients between chambers:

      • Blood flows from high-pressure areas to low-pressure areas.

      • This pressure change drives the heart's mechanics and valve function.

  • Pressure Gradients:

    • Following electrical activation (EKG waveforms), observe corresponding pressure changes in the atria, ventricles, and aorta indicating contraction and relaxation phases.

Anatomical Consequences of Valve Malfunction

  • Valve Damage:

    • Issues with chordae tendineae or valve flaps can lead to regurgitation (blood flowing backward).

    • Symptoms range from mild fatigue to severe heart function impairment, necessitating valve replacement surgery, often using pig valves or artificial options.

    • Importance of preserving heart valve integrity highlighted through aging effects on connective tissue, causing hardening and inefficiency over time.

robot