Compensatory mechanism – Counterregulatory mechanism

Compensatory mechanism

• Renin-Angiotensin-Aldosterone-System (RAAS)
• Neurohormonal response – RAAS
• Endothelin release (contractility)
• Cytokine release (Hypertrophy)
• Inadequate stroke volume and CO –  (Epi and NoreEpi)
• Ventricular remodeling
  • Continuous activation of neuro-hormonal responses (RAAS and SNS)
  • Hypertrophy of ventricular myocytes
  • Ventricles larger but less effective in pumping
  • Can cause life-threatening dysrhythmias and sudden cardiac death
• Dilation
  • Enlargement of chambers of heart that occurs when pressure in left ventricle is elevated
  • Initially effective
  • Eventually this mechanism becomes inadequate and CO decreases
• Hypertrophy
  • Increase in muscle mass and cardiac wall thickness
  • Initially effective
  • Over time leads to poor contractility, increased O₂ needs, poor coronary artery circulation, and risk for ventricular dysrhythmias

Counterregulatory mechanism

• Natriuretic peptides
  • Atrial natriuretic peptide (ANP),
    b-type natriuretic peptide (BNP)
  • Released in response to increased blood volume in heart
  • Causes diuresis, vasodilation, and lowered BP
  • Counteracts effects of SNS and RAAS
• Nitric oxide (NO) and prostaglandin
  • Released from vascular endothelium in response to compensatory mechanisms
  • NO and prostaglandin relaxes arterial smooth muscle, resulting in vasodilation and decreased afterload