Blood Pressure Regulation | RAAS & Antihypertensive Drug Classes

Baseline Blood Pressure Regulation

BP equals cardiac output times resistance, tuned by RAAS.

Core eq.: BP = CO × SVR (hemodynamic identity)
<120: Normal systolic target (mmHg, resting)
↓ Renal perfusion: RAAS trigger (juxtaglomerular cells)
Na⁺/H₂O retention: Aldosterone effect (raises volume)

Cardiac output and vascular resistance

Short placeholder: CO and SVR multiply to set arterial pressure.

The RAAS cascade

Short placeholder: renin cleaves angiotensinogen, ACE makes AII.

Feedback and homeostasis

Short placeholder: baroreceptors and kidneys close the loop.

Placeholder key insight: RAAS is slow but powerful BP modulator.

Hypertension Develops

Elevated resistance or volume pushes BP above healthy target.

≥140/90: Stage 2 HTN threshold (mmHg, AHA/ACC)
~1.3 B: Global adults affected (placeholder estimate)
↑ Renin: Overactive RAAS (drives AII overshoot)
Stroke, CKD, MI: Chronic risk (end-organ damage)

Rising vascular resistance

Short placeholder: chronic vasoconstriction narrows arterioles.

Volume overload

Short placeholder: excess sodium retention expands blood volume.

RAAS overactivation

Short placeholder: persistent renin drive sustains hypertension.

Placeholder key insight: severity varies mild to severe.

Drug Class Selection

Each drug class intercepts a different point in the pathway.

RAAS cascade: ACEi/ARB target (blocks AII formation/action)
Vascular smooth muscle: CCB target (direct vasodilation)
Renal Na⁺ handling: Thiazide target (reduces blood volume)
3: Drug classes shown (first-line options)

ACE inhibitors and ARBs

Short placeholder: block angiotensin-converting enzyme or receptor.

Calcium channel blockers

Short placeholder: relax smooth muscle, widen arterioles directly.

Thiazide diuretics

Short placeholder: promote renal sodium and water excretion.

Placeholder key insight: mechanism guides class choice.

Drug class quick reference

Product	Indication	Trial Design	Key Result
ACE Inhibitor / ARB	RAAS cascade	Blocks AII formation or receptor binding	Preferred in diabetes, CKD
Calcium Channel Blocker	Vascular smooth muscle	Blocks Ca²⁺ influx, direct vasodilation	Effective in Black patients, elderly
Thiazide Diuretic	Renal sodium reabsorption	Increases Na⁺/H₂O excretion, lowers volume	Low cost, strong evidence base

Mechanism-Specific BP Lowering

The chosen drug visibly blocks its node; BP output falls.

↓ AII, ↓ SVR: ACEi/ARB effect (cascade interrupted)
↓ SVR directly: CCB effect (resistance dial narrows)
↓ Volume: Thiazide effect (reservoir drains)
8–12 mmHg: Typical SBP drop (monotherapy, placeholder)

Blockade visualized

Short placeholder: block icon appears at the targeted node.

Downstream consequence

Short placeholder: flow past the block point drops sharply.

Gauge response

Short placeholder: BP needle eases toward target zone.

Placeholder key insight: mechanism explains onset timing.

BP Returns Toward Target

Pressure normalizes; patient factors guide class selection.

<130: Target SBP (mmHg, most adults)
CCB/thiazide: Race-guided first-line (placeholder, Black patients)
ACEi/ARB: Diabetes/CKD first-line (renal protection)
CCB favored: Elderly consideration (placeholder guidance)

BP normalization

Short placeholder: gauge needle settles into green target zone.

Patient-factor guidance

Short placeholder: age, race, comorbidities steer drug choice.

Long-term management

Short placeholder: combination therapy often needed over time.

Placeholder key insight: individualized therapy improves outcomes.

BP Regulation & Rx