Renin-angiotensin-aldosterone system

• Triggers for Renin Release
  • ↓ BP: Detected by juxtaglomerular (JG) cells in the afferent arteriole.
  • ↓ Na+ delivery: Detected by macula densa cells in the distal convoluted tubule (DCT).
  • ↑ Sympathetic tone: β1-adrenergic receptor stimulation of JG cells.
• Pathway/Cascade
  • Renin (secreted by JG cells in kidney) converts angiotensinogen (from liver) → angiotensin I.
  • Angiotensin-converting enzyme (ACE) (primarily in lung capillary endothelium) converts angiotensin I → angiotensin II.
    • Hemodynamic Efficiency: The lungs are the only organ that receives 100% of the cardiac output (right ventricle output).
    • ACE is also responsible for the breakdown of bradykinin (a vasodilator).

ACEI

• Physiologic Effects:
  • $\downarrow$ Angiotensin II $\to$ vasodilation ($\downarrow$ SVR), preferentially induces efferent arteriolar vasodilation in glomerulus $\to$ $\downarrow$ intraglomerular hydrostatic pressure.
  • $\downarrow$ Aldosterone $\to$ $\downarrow$ ${\text{Na}}^{+}/{\text{H}}_2\text{O}$ reabsorption, $\downarrow$ ${\text{K}}^{+}/{\text{H}}^{+}$ excretion ($\to$ risk of hyperkalemia).
  • $\downarrow$ Inactivation of bradykinin & substance P $\to$ $\uparrow$ bradykinin levels ($\to$ cough, angioedema).