Renin-Angiotensin-Aldosterone System (RAAS): MCAT Mastery

Blood pressure regulation is critical for survival—and for MCAT success. One of the most testable mechanisms is the Renin-Angiotensin-Aldosterone System (RAAS). Whether it's passage-based physiology or hormone signaling logic, you’ll need to know this cold. Let’s simplify it with a clear diagram, high-yield notes, and MCAT-ready associations.

🔄 Step-by-Step RAAS Cascade

Step	Molecule/Action
1. Renin release	From JG cells in kidney
2. Angiotensinogen cleaved	Liver → Angiotensin I
3. ACE converts it	Lungs: Angiotensin I → Angiotensin II
4. Angiotensin II effects	↑ Vasoconstriction, ↑ ADH, ↑ Aldosterone
5. Aldosterone released	Adrenal cortex → ↑ Na⁺ reabsorption
6. Blood pressure increases	Water follows Na⁺ → ↑ Volume & Pressure

💡 Effects of RAAS on the Body

Target Organ	Action
Blood vessels	Vasoconstriction via angiotensin II
Kidneys	Aldosterone ↑ Na⁺/H₂O reabsorption
Brain	Stimulates ADH release and thirst
Adrenal glands	Produce aldosterone

🧪 MCAT Experimental Example

✅ Question Example:

"A patient taking ACE inhibitors has reduced BP and increased plasma renin..."

Answer: ACE is blocked → less angiotensin II → no aldosterone → Na⁺ not reabsorbed → BP stays low
🧠 ACE inhibitors are a favorite pharmacology angle for test passages!

🔁 RAAS vs ADH

Hormone	Source	Trigger	Action
Aldosterone	Adrenal cortex	Angiotensin II	Na⁺/H₂O reabsorption in distal nephron
ADH (Vasopressin)	Posterior pituitary	High blood osmolality	Water retention in collecting duct

🧠 MCAT Tip: Aldosterone regulates volume, ADH regulates osmolality.

🧠 Final MCAT Tips

• Know the sequence: Renin → Ang I → Ang II → Aldosterone

• Understand where each hormone comes from and what it acts on

• Be ready to analyze medications (like ACE inhibitors or angiotensin blockers)

• Associate low BP or dehydration with RAAS activation

✅ Call-to-Action (CTA)

RAAS doesn’t have to be confusing. Use King of the Curve’s visual tools, adaptive questions, and daily concept drills to lock it in.

👉 Start your free KOTC trial now

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