The Origin Of Thrombi And Virchow's Triad

Question 1

Virchow’s trid describes….?

Answer 1

The 3 primary abnormalities that lead to thrombus formation

Question 2

What are Virchow’s triad?

Answer 2

• Endothelial injury
• Alterations in normal blood flow (turbulence/stasis)
• Hypercoaculability

Question 3

Describe how endothelial injury leads to thrombi formation

Answer 3

Endothelial exposure leads to the exposure of the ECM, platelet adhesion and release of tissue factor. As well as local depletion of PGI2 and plasminogen activators.
The endothelium doesn’t need to be denuded or physically dysrupted, endothelial dysfunction is sufficient to cause thrombosis

Question 4

Describe how endothelial dysfunction contributes to throbosis

Answer 4

Dysfunctional endothelial cells can produce more procoagulant factors or less anti-coagulant factors

Question 5

Which factors can induce endothelial dysfunction?

Answer 5

• Hypertension
• Turbulent blood flow
• Bacterial endotoxins
• Radiation
• Metabolic abnormalities (homocystinemia or hypercholesterolemia)
• Toxins from cigarette smoke

Question 6

How does turbulent blood flow contribute to thrombi formation?

Answer 6

It creates countercurrents and pockets of stasis and stasis is a major contributor in the development of venous thrombi.
Stasis and turbulence promote endothelial activation, enhancing procoagulant activity (due to flow induced changes in endothelial cells gene expression)

Question 7

When _________ flow is disrupted, platelets come into contact with _____________ and prevent washout and dilution of activated _________________ by fresh flowing blood

Answer 7

Laminar; the endothelium; clotting factors

Question 8

How do ulcerating atherosclerotic plaques favour thrombosis?

Answer 8

• they expose ECM

- they cause turbulence

Question 9

Why are aneurysms fertile sites for thrombosis?

Answer 9

They favour local stasis

Question 10

Which conditions favour stasis? (Hence predispose for thrombosis)

Answer 10

• hyperviscosity

- sickle cell anemia

Question 11

Is hypercoagulability a frequent cause of thrombosis?

Answer 11

Not really

Question 12

Name some possible causes of hypercoagulability

Answer 12

• Primary causes: Mutation in factor 5 gene or prothrombin gene
• Acquired causes: Heparin-induced thrombocytopenia syndrome, smoking, obesity etc