Hemostais and Thrombosis

9 important questions on Hemostais and Thrombosis

What is primary and secondary hemostasis?

- Primary: vasoconstriction followed by rapid formation of a platelet plug
- Secondary: stabilization of platelet plug by a fibrin network

Where is the von Willebrand factor (VWF) stored?

In Weibel-Palade bodies located in endothelial cells.

How do platelets adhere to a damaged vessel wall during primary hemostasis?

Vascular damage --> collagen gets exposed --> collagen attracts von Willebran factor (VWF) --> VWF binds to collagen --> GP1B binds to VWF --> platelet activation --> platelets bind to collagen by GPVI and a2Beta1 --> extra activation (2ADP released by dense granules).
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How does a vitamin K antagonist work and what does it treat?

It prevents thrombosis.
The vitamin K antagonist inhibits vitamin K epoxy-reductase thereby limiting the activity of the vitamin K dependent carboxylase. Reduced gamma-carboxylation of blood coagulation results in reduced ability to interact with phospholipids and a reduced activity. So less clotting.

What is hemophilia a and b and how can it be treated?

- Hemophilia a: Lack Factor VIII
- Hemophilia b: Lack Factor IX
Result: bleeding in joints or muscle (joint bleeding may result in severe damage)

Patients are treated with:
- purified factor VIII or purified factor IX (intravenous administration)
(sometimes the proteins are recognized as foreign, which induces an immune reaction).
- Bispecific anitobody (Hemophilia a): brings FIXa and FX together (so does the  same as FVIII). Is however still less effective than FVIII istself.
- Gene therapy

How does secondary hemostasis go?

- Complex VII modifies carboxyl groups more efficient which leads to better binding to phospholipids.
- Complex VIIa activates factor X and factor IX.
- Factor Xa and IXa lead to the formation of thrombin and that leads to the formation of fibrin. (FIXa accelerates serine protease).

* Complex FXa and FVa converts prothotrobin into thrombin (which activates FV, FVIII and FXI --> amplification thrombin formation)
* Thrombin cleaves fibrogen which forms fibrin by releasing fibrinopeptiole A and B. 
* Fibrin crosslinks due to Ca2+binding

How are fibrin clots degraded?

- Plasminogen is converted into Plasmin. Plasmin removes fibrin clots.

How can blood coagulation be controlled?

- Anti thrombin (AT) inhibits FIXa, FXa and thrombin.
- APC (Activated Protein C) + ProtS (active component) cleave FVa and FVIIIa (cofactors) which lead to a limited thrombin formation.

What happens in Factor V Leiden?

There is a mutation in the FV position where APC (Activated Protein C). So APC cannot cleave anymore and FV circulates longer in the bloodstream which leads to a higher chance of thrombosis.

* Treatment: vitamin K antagonist

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