Haemostasis Flashcards
What is Haemostasis?
The process in which blood coagulation is initiated and terminated in a tightly regulated fashion together with the removal of the clot
What is the first step of haemostasis?
Vasoconstriction restricts blood flow to the vessel
What is primary haemostasis?
The second stage, platelet aggregation that forms a plug
What is secondary haemostasis?
Generation of the enzyme thrombin that converts soluble fibrinogen to insoluble fibrin
What is Fibrinolysis?
Removal of the clot
What is the haemostatic system?
a mosaic of activating or inhibitory pathways
What are the five major components of the haemostatic system?
Blood vessels
– Platelets
– Coagulation factors
– Coagulation inhibitors
– Fibrinolytic factors (clot dissolving components)
Why must haemostasis be regulated?
to prevent inappropriate clot formation
What can happen when blood vessels are blocked?
Restricting blood flow
Starving tissues of oxygen
Leading to cell death
Where are platelets produced?
In the bone marrow
Where are coagulation proteins produced?
Primarily made in the liver
Why is haemostasis so rapid?
all the components are pre-synthesised and circulating in the blood
How do activated platelets generate thrombin?
they expose a surface that promotes the assembly of complexes leading to local generation of thrombin
What does the undisturbed endothelium present?
An anticoagulant response that dampens the activation of coagulation
What does the anticoagulant response do?
limits spread of the response beyond the injury
Where are platelets produced?
Bone marrow
What is Thrombopoietin?
Glycoprotein that regulates the production of platelets
What is thrombocytopenia?
Deficiency in circulating platelets due to decreased platelet formation
What are megakaryocytes?
hematopoietic cells that are responsible for the production of platelets
What is the purpose of the adhesion molecules found on the surface
To recognise components in the matrix e.g collagen and VWF
What occurs when platelets bind to ligands? (such as collagen)
release of granules containing ADP and thromboxane that activates the platelet
What does the exposure of phosphotidylserine (PS) on the platelet surface lead to?
The negatively charged surface promotes thrombin generation and fibrin deposition
What occurs to VWF under sheer stress?
It unfolds, exposing platelet binding sites. These can then bind to platelets as they go past
What does localised thrombin generation lead to?
further platelet activation and formation of a polymerised fibrin mesh