The Renin-Angiotensin-Aldosterone System (RAAS)

Jun 29, 2024

The Renin-Angiotensin-Aldosterone System (RAAS)

Overview

  • Homeostatic negative feedback loop
  • Regulates blood pressure, blood volume, and sodium levels
  • Involves kidneys, other organs, hormones, and enzymes

Four Parts of Homeostasis Loop

  1. Stimulus/Change: Dehydration, blood loss, sodium deficiency
  2. Sensors: Detect changes
  3. Integration: Compare value to set point, decide corrective action
  4. Effectors: Implement changes to restore balance

Stimuli and Initial Responses

  • Dehydration/Blood Loss: Decrease in blood volume and pressure
  • Sodium Deficiency: Detected by chemoreceptors

Sensors

  • Baroreceptors: Detect blood pressure drop, found in nephron's juxtaglomerular cells (afferent arterioles)
  • Chemoreceptors: Detect sodium levels, found in macula densa of distal convoluted tubule

Integration

  • Key Organs: Liver, kidneys, lungs
  • Angiotensinogen: Produced by liver, inactive hormone

Conversion Process

  1. Renin Release: By juxtaglomerular cells in response to low blood pressure or sodium signal
  2. Renin Function: Converts angiotensinogen into Angiotensin I
  3. ACE (Angiotensin-Converting Enzyme): Converts Angiotensin I to Angiotensin II

Angiotensin II Effects

  1. Aldosterone Production: Stimulates adrenal gland
    • Increases sodium reabsorption in distal convoluted tubule
    • More sodium reabsorption leads to more water reabsorption, increasing blood volume/pressure
  2. Direct Impact on Nephron:
    • Increases sodium reabsorption in proximal convoluted tubule
  3. Pituitary Gland Stimulation:
    • Releases ADH (Antidiuretic Hormone), also known as vasopressin
    • Increases water reabsorption in distal convoluted tubule and collecting duct
  4. Vasoconstriction: Constricts blood vessels, increasing blood pressure
  5. Sympathetic Nervous System Activation: Enhances fight-or-flight response, increasing blood pressure
  6. Glomerular Filtration Rate (GFR): Increases GFR to maintain waste filtration despite low blood pressure/volume

Key Points to Remember

  • Renin: Enzyme, not hormone
  • ACE Inhibitors: Blood pressure medication
  • Angiotensin II: Main hormone that triggers multiple effects

Study Tips

  1. Pause and review diagram explanations
  2. Practice with blank diagrams
  3. Draw the entire process from memory

Extra

  • Fun Fact: Telling anatomy-related jokes can lighten up the studying mood!

Note: This content is helpful for understanding the steps involved in blood pressure regulation and the roles of different organs and hormones.