Renin-Angiotensin-Aldosterone System (RAAS)

Key Functions of RAAS

• Goal: Raise blood pressure
• Starts with kidneys

Kidney Function

• Kidneys receive ~20% of cardiac output
• Filter blood at 100-120 mL/min (filtration rate)
• Decrease in filtration rate (e.g., 80 mL/min) indicates low blood volume

Response to Low Filtration Pressure

• Kidneys release enzyme renin
• Renin acts on substrate angiotensinogen (from liver)
  • Angio (blood vessel) + Tensin (tension/pressure) indicates involvement in blood pressure

Conversion Process

1. Renin cleaves angiotensinogen -> forms Angiotensin 1
   • Angiotensin 1: inactive, no physiological value
2. Angiotensin 1 travels to lungs
3. Lung cells have enzyme ACE (Angiotensin Converting Enzyme)
4. ACE converts Angiotensin 1 -> Angiotensin 2 (active form)

Actions of Angiotensin 2

• Angiotensin 2 (active) acts on 3 major organs to raise blood pressure

1. Adrenal Cortex

• Angiotensin 2 binds to receptors in adrenal cortex
• Adrenal cortex produces aldosterone
  • Aldosterone tells kidneys to reabsorb salt and water -> increases blood volume -> raises blood pressure

2. Muscular Arteries

• Angiotensin 2 binds to endothelial receptors
• Causes vasoconstriction
  • Constriction of blood vessels increases pressure on vessel walls -> raises blood pressure

3. Posterior Pituitary Gland

• Angiotensin 2 affects neurons in hypothalamus
• Hypothalamus releases ADH (Anti-Diuretic Hormone)
  • ADH tells kidneys to reabsorb more water -> increases blood volume -> raises blood pressure

Additional Insights

• Blood pressure medications may inhibit parts of this process to lower blood pressure
• Further learning in related video on blood pressure medications