Cardiac homeostasis

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  • Cardiac homeostasis
    • Preload
      • passive stretch placed on a muscle prior to an active contraction; initial passive length to which muscle is stretched prior to the start of a contraction
    • Frank-Starling curve
      • Normal heart - As you increase preload, you increase stroke volume
      • Failing heart - this relationship is lost, heart loses its ability to pump increased blood round body
    • Afterload
      • force a muscle experiences (exerts) after it has begun to shorten, force heart has to beat against (aortic pressure)
    • Frank-Starling law
      • The stroke volume of the heart increases in response to an increase in the volume of blood filling the heart when all other factors remain constant.
    • Caculations
      • MABP= CO x TPR
        • Fall in MABP is detected by arterial baroreceptors
          • Causes reflex
            • sympathetic arteriolar constriction in skin and viscera
            • sympathetic cardiostimulation
            • sympathetic veno-constriction
      • CO = SV x HR
        • CO can increase 4-5 fold during exercise
          • This is cardiac reserve. In HF this is diminished or abolished
    • Haemodynamics
      • physics of blood flow and distributions
    • Ventricular function curves
      • A biological property of muscle increases in resting length causes increase in development of tension/contractionMore you stretch cardiomyocytes, the more tension they have
    • Contractility and venous return
      • Increased cardiac contractility (Sympathetic stimulation) and decreased resistance (as occurs during exercise) will produce maximum increases in CO.
      • Sympathetic venoconstriction may further enhance venous return. Note that changing cardiac contractility (pump output) also changes Rt Atrial Press

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