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

Overview

• RAAS is a hormone system that regulates blood pressure and fluid balance.
• Activates in response to fluid volume deficit (low blood pressure).
• Main goal: Increase blood pressure by increasing blood volume.

Key Components

1. Renin

   • Released by juxtaglomerular cells in the kidneys in response to low blood pressure.
   • Initiates the RAAS pathway.

2. Angiotensinogen

   • Produced by the liver.
   • Converted to Angiotensin I by renin.

3. Angiotensin I

   • Precursor to the active hormone Angiotensin II.
   • Converted to Angiotensin II by Angiotensin-Converting Enzyme (ACE).

4. Angiotensin II

   • Major hormone for increasing blood pressure.
   • Causes vasoconstriction, leading to higher blood pressure.
   • Stimulates release of other hormones:
     • Aldosterone from the adrenal cortex.
     • Antidiuretic Hormone (ADH) from the posterior pituitary gland.
   • Stimulates the thirst mechanism.

Mechanisms of Action

• Vasoconstriction

  • Narrows blood vessels, reducing blood flow to kidneys.
  • Reduces water excretion, aiding in fluid retention.

• Aldosterone

  • Promotes sodium retention in kidneys, leading to water retention.
  • Results in decreased urination and increased blood volume.

• Antidiuretic Hormone (ADH)

  • Promotes water retention in the kidneys.
  • Works against the action of diuretics by reducing urination.

• Thirst Mechanism

  • Increases the desire to drink more fluids, contributing to increased blood volume.

Implications

• Low Blood Pressure: RAAS activation is crucial to restore normal blood volume and pressure.
• Fluid Volume Deficit: Understanding RAAS helps in managing conditions associated with fluid imbalance.

Additional Resources

• For more videos on fluid and electrolyte balance, refer to the provided YouTube links.