22. Pathophysiology of Thrombosis and Embolism Flashcards
How is normal blood flow described as?
Laminar; when blood flows in parallel layers with no disruptions between layers
What properties make blood flow laminar in normal conditions? (5)
- pressure gradient
- resistance (due to diameter)
- viscosity of blood
- velocity of blood
- compliance (muscular arteries less compliant than elastic)
What is the term that describes stagnant blood flow?
Stasis
What is the term that describes forceful and unpredictable flow?
Turbulence (blood swirling around, not smooth, rhythmic or laminar)
What is the most common defect in blood flow?
Thromboembolism
What are other causes for defects in blood flow?
- atheroma
- hyperviscosity
- spasm
- external compression (e.g. tumour)
- vasculitis (inflammation of vessel wall)
- vascular steal
What is the name of the group of factors that cause thrombosis?
Virchow’s Triad
What 3 factors make up the Virchow’s Triad which cause thrombosis?
- changes in blood vessel wall (endothelial injury/ dysfunction)
- changes in blood constituents (hypercoagulability; increase in clots)
- changes in pattern of blood flow (haemodynamic changes e.g. stasis or turbulence)
What is the difference between clot and thrombus?
Thrombus: formation of a solid mass from the constituents of blooth within the vascular system during life; i.e. when it’s dangerous in a healthy blood vessel
Clot: outwith vascular system or formed in a health vessel as a response to damage to a vascular tissue
What 2 constituents make up an atheroma?
- fibrous cap
2. lipid core
What is the main pathogenesis of changes to blood vessel wall causing a thrombus?
endotherlial injury/dysfunction
What is the main pathogenesis to blood flow causing a thrombus?
stasis or turbulent blood flow (abnormal blood flow)
What is the main pathogenesis to changes in blood constituents which causes a thrombus?
Hypercoagulability of the blood (increase in coagulation which causes a thrombus)
What occurs on the endothelial lining in the blood vessel when a thrombus is formed?
endothelial surface is lost which causes RBCs and platelets to be deposited on plaque forming the thrombus
Describe the steps which occur when thrombosis occurs. (8)
- atheromatous coronary artery exists
- turbulent/rapid blood flow occurs leading to fibrin deposition and platelet clumping
- loss of intimal cells and denuded/stripped plaque
- collagen is exposed and platelets adhere/ stick to it
- fibrin meshwork forms and RBCs are trapped
- alternating bands; lines of Zahn (layers of platelets mixed with fibrin and dark RBCs characteristic of thrombus)
- leads to further turbulence and platelet deposition
- propagation/spreading and consequences
What is the biggest risk factor for atheromas and thrombosis which are caused by Virchow’s triad?
Hypercholesterolaemia
What is arterial thrombosis most commonly formed/ imposed on?
most commonly formed on atheroma (atheromatous plaque) which indicates relationship between atheroma and thrombosis
What are lines of Zhan?
- characteristic of a thrombi
- visible layers (laminations) of platelets, fibrin meshwork and RBCs
- its presence indicates thrombosis due to turbulent blood flow
Where is the turbulent flow greatest?
At the end of a thrombus
What is meant by turbulent flow?
- fluid undergoes irregular fluctuations and mixing (in contrast to laminar flow where fluid moves in smooth and parallel layers)
- speed of fluid is continuously undergoing changes in both magnitude and direction
Define thrombosis.
- LOCAL coagulation or clotting of blood in a blood vessel (not travelling but localised blood clot).
- Thrombus formed due to changes in blood vessel wall
Give an example of when blood constituents often change which leads to thrombosis.
When blood undergoes hyperviscosity and post-traumatic hypercoagulaility after a trauma/injury or post surgery as an automatic mechanism
When is stasis blood flow most common?
- “economy class syndrome”
- common in post- op as blood travels more slowly