Haemostasis Flashcards
Haemostasis definition
Haemostasis is the balance between blood clotting and clot lysis
It works to control bleeding and prevent thrombosis
Mechanisms of haemostasis
- Blood vessels
- Platelets
- Blood coagulation
- Fibrinolysis
Platelets
Platelets provide early stage clotting
They adhere to collagen that is exposed by a wound and become activated
Many platelets cluster around the injury to form a haemostatic plug
Blood coagulation
The blood coagulation pathway involves the activation of clotting factors to produce thrombin
Most clotting factors are synthesised in the liver
They lead to the formation of fibrin, which is a more permanent plug
Fibrinolysis
The fibrinolysis pathway produces plasmin
Plasmin degrades fibrin fibres
Bleeding time
Bleeding time is an index of platelet integrity
APTT
Activated partial thromboplastin time tests the intrinsic blood coagulation pathway
PT
Prothrombin time tests the extrinsic blood coagulation pathway
Platelet abnormalities
Can occur due to thrombocytopenia and abnormal platelet function
Symptoms = purpura, bleeding from mucous membranes
Thrombocytopenia
Characterised by abnormal levels of platelets in the blood
May be due to reduced production, increased destruction or sequestration
Idiopathic thrombocytopenic purpura
A bleeding disorder caused by the immune destruction of platelets
Leads to the destruction of the spleen
Symptoms = easy bruising, purpura, epistaxis, menorrhagia, major haemorrhage
Treatment of idiopathic thrombocytopenic purpure
In children, the disease may be self-limiting
Anti-inflammatory steroids may help
A splenectomy may be required
Haemophilia A
A deficiency of factor VIII (8)
X-linked recessive trait
Affects the intrinsic pathway leading to significant bleeding after minor trauma
Haemophilia B
A deficiency of factor IX (9)
X-linked recessive trait
Affects the intrinsic pathway
Von Willebrand’s disease
A deficiency or abnormality of VWf
Results in abnormal platelet adhesion
Autosomal trait
