Day 5- Lecture 2- Thrombosis And Embolism Flashcards
What is thrombosis?
The process of formation of a thrombus
When does thrombosis occur?
When normal haemostatic mechanisms are turned on inappropriately
What is a thrombus?
A solid mass formed from the constituents of the blood within the heart of vessels during life
What are the 3 changes in Virchow’s triad that explain the process of thrombosis?
- Changes in vascular wall (endothelial damage)
- Changes in blood flow (slow or turbulent flow)
- Changes in blood (hypercoagulability)
Where do arterial and cardiac thrombi normally occur?
At the site of endothelial injury or turbulence
When is venous thrombi often seen?
Where there is stasis
Which 2 of aspects of Virchow’s triad would produce a thrombus?
- Changes in blood flow (stasis)
- Hypercoagulability
Stasis and hypercoagulability are present in pregnancy when there is stasis due to pressure on the large veins of the pelvis by the gravid uterus and the blood is hypercoagulable. What is the consequence of this?
Increased risk of thrombi in the lower limbs
When can endothelial damage take place?
- After a myocardial infarction (there is damaged to area of endothelium overlying the infarct)
- Secondary to haemodynamic stress of hypertension
- Scarred heart valves
- After trauma or surgery
- In inflammation
- On the surface of atherosclerotic plaques when they break open
When there is endothelial damage, what happens?
The platelets adhere to exposed von willebrand factor/factor VIII complex
Why does a thrombus not normally form when blood flow is swift (i.e. No stasis)?
The platelet thrombi generally does not grow as the current washes away the platelets, chemical mediators and clotting factors
What occurs with abnormal flow?
- Gives platelets a better chance to stick to the endothelium
- Gives clotting factors a change to accumulate
Why is thrombosis more frequent in veins?
- As they have slower flow
- Valves produce eddies (swirling of blood) and pockets of stagnant blood
When is blood flow particularly slow in veins?
- Cardiac failure
- Patients who are immobile/bed rest use to lack of muscular contractions in the calves results in blood stasis
This predisposes these patients to thrombosis
When else is slow/turbulent flow seen?
- Over ulcerated atherosclerotic plaques
- Within aneurysms
- Around abnormal heart valves
- In the heart where a section of the myocardium isn’t contracting following an MI
Turbulent flow can itself cause endothelial damage- and abnormal flow also allows thrombi to grow more easily
