STEP 1 — MCQs (NO answers here)
MCQ 1 — Virchow Triad
The three primary abnormalities that predispose to thrombosis are:
a. Platelet deficiency, anemia, endothelial regeneration
b. Endothelial injury, stasis/turbulence, hypercoagulability
c. Vasodilation, high cardiac output, hypercalcemia
d. Fibrinolysis, vasoconstriction, leukocytosis
e. Atherosclerosis, infection, thrombocytopenia
MCQ 2 — Thrombosis in Arteries
Thrombus formation in the heart and arterial circulation typically depends on:
a. RBC aggregation
b. Platelet-rich clots due to endothelial injury and high shear stresses
c. Very low blood flow allowing fibrin accumulation
d. Lymphatic obstruction
e. Fat embolism
MCQ 3 — Platelet-Rich Arterial Thrombi
Arterial thrombi are usually rich in platelets because:
a. Platelets die quickly in venous blood
b. High shear forces require platelet adhesion and activation for clot formation
c. Fibrin cannot form in arteries
d. Tissue factor is absent in arteries
e. RBCs dominate arterial flow
MCQ 4 — Purpose of Aspirin in CAD/MI
Aspirin is used in coronary artery disease because:
a. It increases fibrin production
b. Arterial thrombosis depends heavily on platelet activation
c. It stimulates endothelial PAI production
d. It enhances vWF release
e. It causes vasoconstriction
MCQ 5 — Endothelial Activation Causes
Endothelial activation (“dysfunction”) may be triggered by all EXCEPT:
a. Physical injury
b. Hypercholesterolemia
c. Inflammatory mediators
d. Abnormal blood flow
e. High oxygen tension in plasma
MCQ 6 — Consequence of Endothelial Activation
Endothelial activation shifts gene expression towards:
a. Anticoagulant and anti-platelet pathways
b. Prothrombotic pathways
c. Vasodilatory dominance
d. Increased t-PA production
e. Decreased PAI release
MCQ 7 — Procoagulant Change: Thrombomodulin
Downregulation of thrombomodulin on activated endothelium results in:
a. Reduced thrombin generation
b. Sustained thrombin activity promoting platelet activation and inflammation
c. Enhanced protein C activation
d. Increased fibrinolysis
e. Inhibition of PAR signaling
MCQ 8 — Other Downregulated Anticoagulants
Activated endothelium promotes thrombosis by downregulating:
a. Heparin
b. Protein C and TFPI
c. Platelet factor 4
d. Collagen
e. Vitamin K
MCQ 9 — Anti-Fibrinolytic Change
Activated endothelial cells favor thrombosis by:
a. Increasing t-PA expression
b. Decreasing PAI release
c. Secreting PAI and reducing t-PA expression
d. Activating plasmin directly
e. Activating protein S
MCQ 10 — Key Prothrombotic Effect of PAI
PAI (plasminogen activator inhibitor) promotes thrombosis because it:
a. Activates plasminogen
b. Blocks fibrin polymerization
c. Inhibits fibrinolysis by blocking plasminogen activation
d. Activates factor XIII
e. Stimulates platelet production
STEP 2 — ANSWERS + SHORT EXPLANATIONS
MCQ 1 — b
Virchow triad: endothelial injury, abnormal blood flow (stasis/turbulence), hypercoagulability.
MCQ 2 — b
Arterial clots form in high-shear environments → require platelet activation triggered by endothelial injury.
MCQ 3 — b
High shear = platelets essential → arterial thrombi become platelet-rich (“white clots”).
MCQ 4 — b
Aspirin inhibits platelet activation → essential because arterial thrombosis is platelet-driven.
MCQ 5 — e
High oxygen tension is NOT listed as a cause.
Causes include injury, inflammation, hypercholesterolemia, homocystinemia, abnormal flow, smoking toxins, infection.
MCQ 6 — b
Endothelial activation shifts the phenotype toward prothrombotic gene expression.
MCQ 7 — b
↓ Thrombomodulin → thrombin remains fully active → sustained thrombin → more platelet activation + inflammation via PARs.
MCQ 8 — b
Activated endothelium downregulates protein C and TFPI → increases coagulation.
MCQ 9 — c
Activated endothelium:
- Secretes PAI
- Reduces t-PA
→ Both inhibit fibrinolysis, promoting clot persistence.
MCQ 10 — c
PAI blocks conversion of plasminogen → plasmin → inhibits fibrinolysis, favoring thrombosis.
STEP 3 — HIGH-YIELD NOTES (COMPLETE + EXAM READY)
Virchow Triad & Endothelial Dysfunction — Full Exam-Ready Integration
1. Virchow Triad — Three Core Drivers of Thrombosis
Thrombosis arises from the combined influence of:
1. Endothelial injury
- Most powerful trigger.
- Exposes vWF and Tissue Factor, initiating platelet adhesion and coagulation cascade.
2. Abnormal blood flow
- Stasis (veins) → allows clotting factors to accumulate.
- Turbulence (arteries, aneurysms) → endothelial injury + pockets of stasis.
3. Hypercoagulability
- Inherited (e.g., Factor V Leiden) or acquired (e.g., malignancy, pregnancy, OCPs).
Key concept: These three factors rarely act alone — thrombosis typically reflects a synergistic interaction.
2. Endothelial Injury — MOST Important in Arterial Thrombosis
Why?
High-flow circulation (heart + arteries) normally resists thrombosis unless the endothelium is disrupted.
Consequences:
- Exposure of vWF → strong platelet adhesion.
- Exposure of tissue factor (TF) → triggers extrinsic pathway → thrombin generation.
Arterial thrombi = platelet-rich (“white thrombi”)
Clinical connection: Aspirin
- Arterial thrombosis is platelet-driven, so inhibiting platelet aggregation reduces MI/CAD events.
3. Endothelial Activation / Dysfunction
Even without full structural damage, endothelium can become prothrombotic.
Triggers:
- Hemodynamic stress (turbulence, hypertension)
- Inflammatory cytokines
- High cholesterol (hypercholesterolemia)
- Homocystinemia
- Toxins from cigarette smoke
- Diabetes/metabolic syndrome
- Infection
Result:
The endothelial phenotype shifts from anti-thrombotic → pro-thrombotic.
4. Prothrombotic Alterations in Activated Endothelium
A. Procoagulant changes
- ↓ Thrombomodulin
- Normally converts thrombin into an anticoagulant signal (activating Protein C).
- When reduced → thrombin stays active, promoting:
- Platelet activation
- Inflammation via PAR (protease-activated receptors)
- ↓ Protein C and ↓ TFPI expression
- Protein C normally inactivates Va and VIIIa.
- TFPI inhibits VIIa–TF complex.(Tissue Factor Pathway Inhibitor)
- Loss = unchecked thrombin generation.
B. Anti-fibrinolytic changes
Activated endothelium:
- ↑ PAI (plasminogen activator inhibitor)
- Blocks t-PA → prevents plasmin formation.
- ↓ t-PA
- Further reduces fibrinolytic activity.
Net effect:
→ Thrombus persists due to impaired breakdown.
5. Integrated Effects on Thrombosis
When endothelial injury or dysfunction occurs, the following prothrombotic changes accumulate:
- ↑ Thrombin generation (major amplifier of coagulation)
- ↑ Platelet adhesion + activation
- ↓ Anticoagulant signals (thrombomodulin, Protein C, TFPI)
- ↓ Fibrinolysis (↑ PAI, ↓ t-PA)
Diseases strongly driven by endothelial dysfunction:
- Myocardial infarction (coronary artery thrombosis)
- Ischemic stroke
- Peripheral arterial disease
- Venous thrombosis (particularly when combined with stasis or hypercoagulability)
High-Yield Exam Hooks
- Endothelial injury = most important factor for arterial thrombosis
- Platelet-rich thrombi → arteries; fibrin-rich → veins
- Cigarette smoke, hypercholesterolemia, homocysteinemia → endothelial activation
- ↓ thrombomodulin = ↑ thrombin = prothrombotic
- PAI ↑ = inhibited fibrinolysis
- Stasis is the MAIN contributor in venous thrombosis