Study guide: Atherosclerosis Pathogenesis and Clinical Implications

1. 📌 Essentials

• Atherosclerosis is a chronic disease characterized by fatty deposits in arterial walls causing stenosis.
• Primarily affects medium to large arteries like coronary, carotid, and peripheral arteries.
• Initiates with endothelial dysfunction due to risk factors such as hypercholesterolemia, hypertension, smoking, and diabetes.
• Lipid infiltration, especially oxidized LDL, promotes inflammation and foam cell formation.
• Progressive stages include fatty streaks, fibrous plaques, and complicated lesions.
• Stable plaques are collagen-rich; unstable plaques are lipid-rich and prone to rupture.
• Critical stenosis >70–75% causes ischemic symptoms; rupture can lead to thrombosis.
• Clinical manifestations include angina, MI, stroke, limb ischemia, often asymptomatic early.
• Plaque development is a slow process spanning decades, beginning in youth.
• Morphological evolution: fatty streak → fibrous plaque → calcified and complex plaque.

2. 🧩 Key Structures & Components

• Endothelium — lines arteries, regulates vessel permeability and tone.
• Lipid core — composed of cholesterol, phospholipids, necrotic debris.
• Foam cells — macrophages engorged with oxidized LDL.
• Vascular smooth muscle cells (VSMCs) — migrate, proliferate, produce collagen.
• Fibrous cap — collagen layer stabilizing plaque.
• Necrotic core — lipid and cell debris prone to rupture.
• Calcifications — deposits within chronic plaques.
• Thrombus — clot formed after plaque rupture.
• Risk factors — hypercholesterolemia, hypertension, smoking, diabetes.
• Risk modifiers — age, sex, obesity, inactivity.

3. 🔬 Functions, Mechanisms & Relationships

• Endothelial dysfunction allows LDL to penetrate intima.
• Oxidized LDL induces monocyte adhesion and infiltration.
• Monocytes differentiate into macrophages, phagocytose lipids forming foam cells.
• Foam cells and lipid accumulation form fatty streaks.
• VSMCs migrate from media to intima, secrete collagen → fibrous cap.
• Stable plaques have thick collagen caps; unstable plaques have thin caps and large lipid cores.
• Plaque rupture exposes thrombogenic material, leading to thrombus formation.
• Critical stenosis (>70–75%) causes ischemic symptoms; rupture causes acute events.
• Calcification stabilizes plaques but can contribute to brittleness.

Endothelium
   │
   ├─ LDL infiltration
   │
   ▼
Oxidized LDL
   │
   ├─ Monocyte recruitment
   │
   ├─ Monocytes → macrophages → foam cells
   │
   ├─ Fatty streak formation
   │
   ├─ VSMC migration and collagen deposition
   │
   └─ Fibrous plaque
           │
           ├─ Stable (thick collagen)
           │
           └─ Unstable (lipid-rich core)

4. Comparative Table: Stable vs. Unstable Plaques

5. 🗂️ Hierarchical Diagram

Atherosclerosis
 ├─ Initiation
 │   └─ Endothelial dysfunction
 ├─ Lipid infiltration
 │   └─ LDL cross-and oxidation
 ├─ Inflammatory response
 │   └─ Monocyte adhesion and infiltration
 ├─ Foam cell formation
 │   └─ Macrophages ingest oxidized LDL
 ├─ Plaque development
 │   ├─ Fatty streak
 │   ├─ Fibrous plaque (VSMC collagen)
 │   └─ Complex/ruptured plaque
 └─ Clinical outcome
     ├─ Chronic ischemia
     └─ Acute rupture leading to thrombus

6. ⚠️ High-Yield Pitfalls & Confusions

• Confusing fatty streaks with advanced plaques; fatty streaks are non-obstructive and benign.
• Mistaking stable plaques for unstable ones; stability depends on collagen content.
• Overlooking the role of oxidized LDL vs. native LDL.
• Ignoring the contribution of VSMCs to plaque stability.
• Misinterpreting the timing: initiation in youth (ages 10–20), symptoms often not until 35–40.
• Assuming all plaques cause symptoms; most early plaques are asymptomatic.
• Confusing atherosclerosis with arteriosclerosis (general arterial stiffening).
• Overemphasizing calcification as a sign of instability; often stabilizes plaques.

7. ✅ Final Exam Checklist

• Define atherosclerosis and identify affected arteries.
• List key risk factors: hypercholesterolemia, hypertension, smoking, diabetes.
• Describe the sequence: endothelial damage → LDL entry → foam cells → fatty streaks.
• Differentiate stable vs. unstable plaques.
• Know the critical stenosis percentage (>70–75%) causing symptoms.
• Understand the process of plaque rupture and thrombus formation.
• Recognize clinical presentations: angina, MI, stroke, gangrene.
• Recognize the significance of oxidized LDL in pathogenesis.
• Describe the morphological evolution of plaques.
• Recall age-related development starting at age 10–20.
• Be aware of factors that stabilize or destabilize plaques (collagen vs. lipids).
• Know the common arteries affected and related diseases.

End of Revision Sheet