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
- Stimulus/Change: Dehydration, blood loss, sodium deficiency
- Sensors: Detect changes
- Integration: Compare value to set point, decide corrective action
- 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
- Renin Release: By juxtaglomerular cells in response to low blood pressure or sodium signal
- Renin Function: Converts angiotensinogen into Angiotensin I
- ACE (Angiotensin-Converting Enzyme): Converts Angiotensin I to Angiotensin II
Angiotensin II Effects
- Aldosterone Production: Stimulates adrenal gland
- Increases sodium reabsorption in distal convoluted tubule
- More sodium reabsorption leads to more water reabsorption, increasing blood volume/pressure
- Direct Impact on Nephron:
- Increases sodium reabsorption in proximal convoluted tubule
- Pituitary Gland Stimulation:
- Releases ADH (Antidiuretic Hormone), also known as vasopressin
- Increases water reabsorption in distal convoluted tubule and collecting duct
- Vasoconstriction: Constricts blood vessels, increasing blood pressure
- Sympathetic Nervous System Activation: Enhances fight-or-flight response, increasing blood pressure
- 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
- Pause and review diagram explanations
- Practice with blank diagrams
- 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.