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Flashcards in MoD 5 Deck (55)
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What four things does successful haemostasis depend upon?

1. Vessel walls
2. Platelets
3. Coagulatory system
4. Fibrinolytic system


Which systems oppose each other to regulate haemostasis?

The coagulatory and fibrinolytic systems


How do blood vessels contribute to haemostasis?

Arteries, veins and capillaires constrict to reduce blood flow (and therefore blood loss) in a mechanism that is not fully understood.


How do platelets contribute to haemostasis?

1. Adhere to the vessel walls
2. Adhere to each other
3. Form a platelet plug
4. Platelet release reaction


What are platelets derived from?



What is the platelet release reaction?

Once platelets adhere they release certain molecules which help stimulate platelet plug formation and the coagulatory system.


Which molecules released in the platelet release reaction help stimulate platelet plug formation?

ADP, thromboxane A2


Name a molecule released in the platelet release reaction that helps stimulate coagulation?

Platelet factor 3


What is coagulation?

A cascade in which a series of inactive components are converted to active components. This results in fibrinogen being converted to fibrin which polymersises and along with platelets forms the haemostatic plug.


What is prothrombin time a useful measure of?

How effective the clotting cascade is in an individual.


Why is coagulation tightly regulated?

1ml of blood contains enough thrombin to convert all the fibrinogen in the body to fibrin. Therefore a balance or proagulant and anti-coagulant forces is required to prevent inappropriate coagulation.


What is thrombophilia?

Thrombophilia is an abnormality of blood coagulation that increases the risk of thrombosis.


List some thrombin inhibitors:

Anti-thrombin III
Alpha 1 anti-trypsin
Alpha 2 macroglobulin
Protein C
Protein S


What can be the consequences of inherited deficiencies in protein C and protein S?

Increased risk of thrombosis.


What is fibrinolysis?

The breakdown of fibrin.


How does fibrinolysis occur?

Plasminogen activators convert plasminogen to plasmin. Plasmin break downs fibrin.


What is the role of protein C in the fibrinolytic system?

Activated by thrombin binding to the endothelial receptor, thrombomodulin, it degrades blood clotting factors (Va and VIIIa).


What is the role of anti-thrombin III (AT3) in the fibrinolytic system?

It binds very tightly to thrombin and Factor X. This is enhanced by heparin binding (though heparin-bound AT3 cannot bind to thrombin attached to thrombomodulin receptors).


Name two plasminogen activators:

Streptokinase and t-PA.


Fibrinolytic therapy is widely used e.g. to to break down fibrin polymers in thrombi blocking the coronary arteries. What molecules do they inject in this therapy?

Streptokinase and t-PA.


What gives the endothelium some anti-thrombin properties?

1. Plasminogen activators
2. Prostacyclin (inhibits platelet activation)
3. Nitric oxide (vasodilator?)
4. Thrombomodulin (cofactor of thrombin-induced activation of protein C)


What is thrombosis?

The formation of a solid mass of blood WITHIN the circulatory system (during life).


What are the three main categories of causes of thrombosis?

1. Abnormalities of the vessel wall
2. Abnormalities of blood flow
3. Abnormalities of blood components


What types of abnormalities to vessel walls can cause thrombosis?

1. Atheroma
2. Direct injury
3. Inflammation


What types of abnormalities to blood flow can cause thrombosis?

1. Stagnation
2. Turbulence


What types of abnormalities to blood components can cause thrombosis?

1. Smoking -> inherently more coagulable blood
2. Post-partum hypercoaguability
3. Post-operation


What do arterial thrombi look like?

1. Pale (lower RBC content than venous thrombi)
2. Granular
3. Lines of Zahn (laminations -> indicate high blood flow when occurred)
4. Lower cell content


What do venous thrombi look like?

1. Soft
2. Gelatinous
3. Deep red
4. Higher cell content


What are the 5 main outcomes of thrombosis?

1. Lysis
2. Propagation
3. Organisation
4. Recanalisation
5. Embolism


What does the outcome 'lysis of thrombosis' involve?

Fibrinolytic system activates and completes dissolves the thrombus restoring blood flow to exactly as it was before.