Week 3 Flashcards
How are platelets formed?
Budding off from megakaryocytes
What is the lifespan of platelets?
7-10 days
What causes platelet adhesion after vessel wall injury in primary haemostasis?
Exposure of collagen and releasing of vWF
What are the two stages of haemostasis?
Primary - formation of platelet plug
Secondary - formation of fibrin clot
What 3 things can use failure of platelet plug formation?
Vascular - loss of collagen
Platelets - decrease in number or function (drugs)
Decrease in vWF
What symptoms would you see in primary haemostasis failure?
Spontaneous bleeding and purpura
Mucosal bleeding - epistaxis, gi, menorrhagia
Intracranial haemorrhage
How can you screen for primary haemostasis failure?
Platelet count
What causes production of megakaryocytes and platelets?
Thrombopoietin
What causes conversion of prothrombin to thrombin?
V/Xa
What causes conversion of fibrinogen into fibrin?
Thrombin
What affect does thrombin have on IX?
Activates it
What 3 things could case failure of secondary haemostasis?
Single clotting factor deficiency
Multiple clotting factor deficiency
Increased fibrinolysis
What 2 tests can you do for fibrin clot formation and what factors do they represent?
Prothrombin time - TF, VIIa
Activated partial thromboplastin time - VIII/IXa
What breaks down fibrin to fibrin degradation products?
Plasmin
What does antithrombin do?
Inactivates Xa and thrombin
What do protein C and S do?
Inactivate Va and VIIIa
What is the commonest cause of platelet plug formation failure?
Thrombocytopenia
What are the 2 causes of thrombocytopenia?
Increased destruction - DIC, immune thrombocytpoenic purpura, hyersplenism
Reduced production
Name 2 causes of reduced platelet function?
Drugs - aspirin, NSAIDS
Renal failure
What mode of inheritance if von willebrands disease?
Autosomal dominant
Name 1 vascular cause of platelet plug formation failure?
Henoch schonlein purpura
What are the 3 causes of multiple clotting factor deficiencies?
Liver failure
Vitamin K deficiency
Complex coagulopathy
What does liver failure cause clotting factor deficiencies?
Because clotting factors are produced in hepatocytes
Which clotting factors are carboxylated by vitamin K?
II, VII, IX, X
What is required for vitamin k absorption?
Bile salts
Name the 3 steps of disseminated intravascular coagulation?
Excessive activation of haemostasis
Microvascular thrombus
Clotting factor consumption
Which types of haemophilia is more common?
A
What factors are involved in haemophilia A and B?
A - VIII
B - IX
What is the normal PT time?
10-14 seconds
Where is the abnormality of PT is prolonged?
Extrinsic pathway
Causes of prolonged PT?
Liver disease, warfarin, DIC
What is the normal APTT time?
30-40 seconds
Where is the abnormality if the APTT is prolonged?
Intrinsic pathway
Causes of prolonged APTT?
Liver disease
Heparin
Haemophilia
DIC
How does Heparin work?
It potentiates anti thrombin
What is the benefit of LMWH over unfractionated?
Less monitoring needed
Name 2 LMWH’s?
Fragmin, dalteparin
How do you monitor unfractionated heparin?
APTT
What can be used to reverse heparin?
Protamine Sulphate
How does warfarin work?
Block ability of vitamin K to carboxylate
How is INR calculated?
Patients PT/Mean normal PT
How does dabigatran work?
Thrombin inhbitor
How to rivaroxiban and apixiban work?
Xa inhbitors
What sort of drugs are needed to treat an arterial thrombosis?
Anti platlets
What sort of drugs are needed to treat a venous thrombosis?
Anti-coagulants
Name 4 risk factors for arterial thrombosis?
High cholesterol
Diabetes
Hypertension
Smoking
Name 2 conditions caused by a stable atherosclerotic plaque?
Stable angina and intermittent claudication
Name 2 conditions caused by an unstable atherosclerotic plaque?
MI or stroke
How does clopidogrel?
ADP receptor antagonist
What type of dipyridamole?
Phosphodiesterase
When should anti platelets be stopped before elective surgery?
7 days
