Haemostasis intro Flashcards
What is primary haemostasis?
Platelets and vasoconstriction for platelet plug
What cells do platelets develop from
Megakaryocytes
Diameter of platelets?
1-4um
Define thrombocytopenia
Low platelet count
<150*10^9
Normal platelet count?
150-400*10^9
Define thrombocytosis
> 450*10^9
Function of the various proteins found inside platelets
Surface proteins: help platelets stick to breaks in vessel wall and to eachother
Granule proteins: help make plug
Contained proteins: Allow platelet to change shape
What causes platelet migration initially?
The collagen that is exposed when blood vessel breaks causes platelet migration and structural change
Describe structural changes that occur when platelets form initial clot
Originally flat (look like plates) Then extend long filaments and filaments from different platelets interlock to make a clot
What is secondary haemostasis
The use of fibrin to stabilise platelet clot
What is the first thing to trigger coagulation cascade
Tissue factor
Where is tissue factor found?
Outside of endothelium
When does extrinsic pathway of coagulation cascade occur?
When a vessel is injured
Describe the extrinsic pathway (excluding common pathway)
- Factor VII is converted to VIIa via tissue factor
- VIIa converts factor X to factor Xa complex (complex including factor Xa, calcium and more)
Describe the common pathway of coagulation cascade?
- Factor Xa converts prothrombin to thrombin
- Thrombin converts fibrinogen to fibrin
- Fibrin forms stable clot
What is the rate limiting step in extrinsic pathway
X->Xa
What measurment is used to test extrinsic and common pathways?
Prothrombin time
When does the intrinsic pathway of coagulation cascade occur?
occurs without injury to vessels
Describe the instrinsic pathway exclusing the common pathway
Factor XII–> Factor XIIa
XIIa converts XI to XIa
XIa converts IX to IXa
IXa converts X to Xa
What tests the intrinsic and common pathway
Activated partial prothrombin time
Describe bleeding time test
Shallow incision made on underside of forearm
Time taken for bleeding to fully stop in measured
Normal is 3-10 minutes
What is INR?
Derived from prothrombin time
Healthy is 0.8-1.2
What is the INR to aim for in patients taking warfarin and heparin
2.0-3.0
What type of feedback loop regulates thrombin production
Positive feedback
