12.1 The Structure & Function of Platelets Flashcards
What is the main function of platelets?
To aid in the clotting of blood
What organelles do platelets contain? Do they contain nuclei?
Platelets contain:
- Granules
- Mitochondria
- Microtubules
They do NOT contain a nucleus.
Outline the process of haemostasis in 3 steps
- Vasoconstriction to reduce blood loss
- Primary haemostasis (platelet plug formation)
- Coagulation
What is the lifespan of a platelet?
7-10 days
List two chemicals that blood vessel endothelium produces to prevent binding of platelets
- Prostacyclin
- Nitric oxide
True or false: endothelium promotes fibrinolysis as an anticoagulant measure.
True
What are the three steps between inactive platelets and a platelet plug
- Adhesion
- Activation
- Aggregation
When a blood vessel is damaged and the endothelial cells are no longer continuous, molecules are exposed that bind to platelets. Give two examples of these
- Subendothelial collagen
- Von Willebrand factor
Which receptor on platelets binds to Von Willebrand factor?
Glycoprotein 1b
Describe the structure of Von Willebrand factor
Long, sticky protein
What two types of granules are in a platelet?
- Dense
- Alpha
What three processes occur during platelet activation?
- Shape change
- Granule secretion
- Receptor activation
What causes platelet activation?
Adhesion to molecules such as collagen and Von Willebrand factor
Describe the role of Thromboxane A2 and ADP in platelet activation
- Released by activated platelets
- Activates itself and surrounding platelets
Thrombin can activate platelets. How is it produced?
During the coagulation cascade.
During autocrine and paracrine activation of platelets, Glycoprotein 2b 3a (GP IIb/IIIa) is produced on the cell surface of platelets. What is it, and what does it do?
- It is a transmembrane fibrinogen receptor
- It binds to fibrinogen and allows aggregation to occur.
Platelet coagulation requires platelets to have a negative surface charge. How is this achieved?
Upon platelet activation, anionic phospholipids become exposed on platelet surface.
Describe the role of fibrinogen using an oversimplified simile
It is like molecular glue
What are some issues that can arise regarding to platelets
- Acute thrombotic events
- Thrombocytopaenia/osis
- Defective platelets
Antiplatelet drug indications
- ACS
- TIA/Stroke
- Peripheral arterial disease
- Primary prevention
Is aspirin an antiplatelet or an antithrombotic?
Antiplatelet
Describe the mechanism of action of aspiring
Inhibits COX-1 enzyme, preventing production of Thromboxane A2 production
Mechanism of action of ADP receptor inhibitors as antiplatelet agents
- ADP is used for autocrine and paracrine platelet activation during clotting
- By blocking this receptor, we inhibit the process of clotting
Phosphodiesterase inhibitors inhibit platelet aggregation. How?
Nobody knows. Genuinely.
List three contraindications for antiplatelet medication
- Active bleeding
- Thrombocytopenia
- Think twice if they’re also on anticoagulants