Renin-Angiotensin-Aldosterone System (RAAS)

Overview

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

Components of a Nephron

• Nephron: Basic functional unit of the kidney
  • Video recommended for nephron functions

Homeostasis Loop

1. Stimulus/Change: Blood pressure/volume alteration,
2. Sensors: Detect changes
3. Integration: Compare to set point, determine action
4. Effectors: Correct the imbalance

Stimuli for RAAS Activation

• Dehydration: Low water levels
• Blood Loss: Decreased blood volume
• Sodium Deficiency: Low sodium levels

Sensors

• Baroreceptors: Detect blood pressure decrease
  • Located in juxtaglomerular (JG) cells in afferent arterioles
• Chemoreceptors: Detect sodium deficiency
  • Located in macula densa of the distal convoluted tubule

Integration

• Angiotensin II Production: Key hormone in the RAAS
• Organs Involved:
  • Liver: Produces inactive angiotensinogen
  • Kidney: Releases renin
  • Lungs: Produce angiotensin-converting enzyme (ACE)

Hormone/Enzyme Functions

• Angiotensinogen (Liver):
  • Inactive precursor of angiotensin
• Renin (Kidney):
  • Converts angiotensinogen to angiotensin I
  • Released from JG cells
• Angiotensin-Converting Enzyme (Lungs):
  • Converts angiotensin I to II

Effects of Angiotensin II

1. Adrenal Gland: Produces aldosterone
   • Aldosterone: Increases sodium reabsorption in the distal convoluted tubule
2. Direct Action on Nephron: Increases sodium reabsorption in proximal convoluted tubule
3. Pituitary Gland: Releases ADH (Antidiuretic Hormone)
   • ADH: Increases water reabsorption in the distal convoluted tubule and collecting duct
4. Vasoconstriction: Constricts arterioles, raising blood pressure
5. Sympathetic Nervous System Activation: Increases heart rate, alertness
6. Glomerular Filtration Rate: Maintains filtration even if blood pressure is low

Key Points for Study

1. Detection of Changes: Baroreceptors (JG cells) and chemoreceptors (macula densa)
2. Hormone Activity: Angiotensinogen, renin, ACE, Angiotensin II, aldosterone, ADH
3. Effectors: Adrenal gland, nephron, pituitary gland, blood vessels, sympathetic nervous system
4. Outcome: Restoration of blood pressure, volume, and sodium levels

Study Recommendations

1. Review provided diagrams, explain each stage
2. Practice on blank diagrams
3. Try drawing the system from memory

Fun Ending

• Anatomy content and humor to keep learning engaging