The Platelet Flashcards
What physiological mediators are secreted by the endothelium to prevent platelet adhesion?
Prostacyclin (PGI2)
Nitric oxide
What mediators are secreted due to endothelial damage, provoking platelet adhesion?
Collagen
von Willebrand Factor
What happens after platelets adhere to the endothelium to stimulate further aggregation?
Platelet adhesion –> degranulation of platelets –> ADP release
-ADP stimulates further platelet aggregation
What is Thromboxane?
Prostaglandin synthesised by platelets
-causes vasoconstriction and aggregation
How does aspirin work?
Irreversibly inhibits COX
Prevents conversion of arachionic acid to endoperoxides (PGI2/TXA2)
Why does aspirin affect platelet cells and endothelial cells differently?
Platelet cells have no nucleus, cannot resynthesise COX (7 days for new platelets)
Endothelial cells have a nucleus, produce more COX
What is Thrombocytopenia?
Abnormally low platelet count
What are the two main causes of thrombocytopenia?
Reduced platelet production in bone marrow
Excessive peripheral destruction of platelets
What are the common causes of reduced platelet production?
Aplastic anaemia
Marrow infiltration
Marrow suppression
What are the common causes of excess platelet destruction?
Immune thrombocytopenic purpura AI causes (SLE, CLL, viruses) Thrombotic thrombocytopenic purpura Haemolytic uraemic syndrome Sequestration
How does Clopidogrel work?
ADP receptor antagonist
- prevents glycoprotein expression
- prevents platelet aggregation
How does thrombocytopenia present?
Mucocutaneous bleeding
-bruising/purpura of skin
-epistaxis/menorrhagia
Major haemorrhage rare
What is immune thrombocytopenic purpura (ITP)?
Autoimmune disorder causing destruction of platelets
How does ITP affect children?
Acute
Self-limiting
Post viral/immunisation
How does ITP affect adults?
Less acute presentation
Mostly women w/ other AI disorders
