Anticoagulants in Blood Collection Systems Flashcards
What does haemostasis contribute to? (3)
- Maintaining blood in a fluid state in the circulation
- Arresting bleeding at site of injury by formation of a haemostatic plug
- Removal of that haemostatic plug when healing is complete
Where are platelets produced?
In the bone marrow
What is the process of platelet formation called?
Thrombopoiesis
How are platelets formed?
The precursor of the Megakaryocyte, the Megakaryoblast arises from a process of differentiation from the haemopoietic stem cell and colony forming unit CFU-GEMM
What is the platelet growth factor and where is it produced?
Thrombopoietin. Produced in the liver and kidneys
How are platelets central to haemostasis?
- Responsible for the initial closure of the defect in the vessel through formation of a platelet plug (Primary Haemostasis)
- Pro and anticoagulant factors stored in platelet granules and are released into microenvironment
- Contain thromboxane, a powerful vasoconstrictor
- Have many glycoprotein receptors which have a role in haemostasis and provide the membrane surface for which activated coagulation factors bind , leading to increased thrombin (clot) generation
Three phases of platelet function
- Platelet Adhesion
- Platelet Activation
- Platelet Aggregation
What happens during platelet adhesion
Platelets adhere to collagen fibres at site of injury
what happens during platelet activation?
With a change in platelet shape, the release of procoagulant molecules from the platelet granules is stimulated. These molecules released, provide platelets with a surface for the reactions of the coagulation factors in the physiological cascade
What happens during platelet aggregation?
Primary reversible aggregation and secondary irreversible aggregation lead to formation of the primary haemostatic platelet plug.
What reduces the level of platelet aggregation?
The drug aspirin
How do platelets bind to the blood vessel upon vessel injury?
Circulating platelets bind to the blood vessel via surface glycoproteins, Gpla and Gplb
How do platelets react to vessel injury (detailed)?
- Upon vessel injury and exposure of the sub endothelium, circulating platelets bind to the blood vessel via surface glycoproteins, GpIa and GpIb.
- The platelets then undergo shape change, becoming spherical and extending pseudopods.
- The intracellular granules move towards the surface and are released into the microenvironment by the mobilization of calcium and the activation of platelets.
What are coagulation factors?
Inert pro enzymes that become activated during haemostasis to arrest bleeding
What do coagulation factors need the presence of to form a haemostatic plug in vivo or a clot in a tube in vitro?
Calcium!
