Understanding the Renin-Angiotensin-Aldosterone System

Mar 16, 2025

Lecture Notes: Renin-Angiotensin-Aldosterone System (RAAS)

Introduction

  • Discussion on the Renin-Angiotensin-Aldosterone System (RAAS)
  • Importance of knowing body pressures for understanding blood flow and metabolism

Mean Arterial Pressure (MAP)

  • Standard MAP: 70-110 mmHg
    • Too high: Vasoconstriction, inadequate kidney filtration
    • Too low: Insufficient pressure for kidney filtration
  • Kidney pressure: 60-90 mmHg
    • High MAP leads to chronic renal damage
    • Low MAP can result in acute kidney injury

Pressure Dynamics in the Body

  • Capillary bed pressure: ~35 mmHg
  • Central Venous Pressure (CVP): 2-6 mmHg
    • Important for understanding low-pressure systems, particularly right heart side

Role of Kidneys in Pressure Regulation

  • Kidneys require specific pressure range
  • Below 60 mmHg, kidneys send a distress signal
  • Activation of RAAS

RAAS Activation Process

  1. Trigger: Blood pressure drop
  2. Liver releases angiotensinogen
  3. Conversion to Angiotensin I
  4. Lungs release ACE (Angiotensin-Converting Enzyme)
  5. Conversion to Angiotensin II
  6. Angiotensin II effects:
    • Systemic vasoconstriction
    • ADH secretion (posterior pituitary)
    • Aldosterone release (adrenal glands)

Overactivation of RAAS

  • Leads to hypertension
  • Medications to block RAAS effects:
    • Renin Inhibitors: Block conversion of angiotensinogen to Angiotensin I
      • Example: Aliskiren
      • Cautions: Avoid grapefruit juice, high-fat meals
    • ACE Inhibitors: Stop conversion of Angiotensin I to Angiotensin II
      • Concerns: Dry cough, angioedema, orthostatic hypotension
      • Example: Enalapril
    • Angiotensin Receptor Blockers (ARBs): Block receptor sites
      • Less side effects than ACE inhibitors
      • Examples: Valsartan, Losartan
    • Aldosterone Antagonists: Used in CHF and cirrhosis
      • Example: Spironolactone
      • Cautions: Potassium levels, fluid management
    • Neprilysin Inhibitors: Effective in CHF
      • Example: Sacubitril/Valsartan (Entresto)
      • Study: Showed reduced cardiovascular death; caution with potassium-sparing diuretics

Summary

  • Understanding of hypertension cascade and RAAS
  • Importance of medication management and side effects
  • Encouragement to seek further clarification if needed

Additional Resources

  • Refer to ATI Pharm 9.0 Chapters 18, 19, and 20 for more detailed information.