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.