Haemostasis Flashcards
What are clots formed from?
Platelets, von Willebrand factor and coagulation factors
What is the role of natural anticoagulants in haemostasis?
Responsible for confining the clot to the area of injury
What is the role of the fibrinolytic system in haemostasis?
Dissolving the clot after ~1 week
What is the role of the vessel endothelium in haemostasis?
Produces substances such as heparans, nitric oxide, prostacyclin, thrombomodulin and TFPI to stop blood from sticking to the surface and aiding flow
What are the signals for clot formation?
Abnormal surface and physiological activators
How does vessel damage trigger clot formation?
When a vessel is damaged, it is exposed to collagen and the platelets recognise this as an abnormal surface. If a tissue is damaged then tissue factor will be released into the circulation at the site and clots are formed
What is present on the surface of platelets to aid in haemostasis?
Platelet has glycoproteins on it’s surface for things such as von Willebrands factor to bind to. There are also receptors for a number of molecules that signal the platelet to become activated and do it’s job
What are the roles of platelets in haemostasis?
Adhere- via glycoproteins
Activation- via receptors
Aggregation- platelets sticking together to form plug
Provide phospholipid surface for coagulation- scramblase flips platelet membrane round so phospholipid membrane is on the outside
How is definitive haemostasis brought about?
Platelet plug is cleaved to form a fibrin clot
What are zymogens?
Unactivated coagulation factors
Describe the extrinsic pathway in clot formation?
Tissue factor binds to factor VII and activates it, which activates factor X, which turns prothrombin into thrombin. Thrombin cleaves the fibrinogen on the surface of the platelet to fibrin and forms a clot
What are the main natural anticoagulants?
Tissue factor pathway inhibitor
Activated protein C and protein S
Antithrombin
