9 - Haemostasis Flashcards
What are the (2) functions of haemostasis?
- prevention of blood loss from intact vessels
- arrest of bleeding from injured vessels
Give an overview of the process that occurs during haemostatic plug formation
vessel constriction —> formation of an unstable platelet plug —> stabilisation of the plug with fibrin —> dissolution of clot and vessel repair (fibrinolysis)
When there is an injury to the blood vessels, which blood vessels constrict?
the smaller ones
What is primary haemostasis?
What does it involve?
formation of an unstable plug
involves platelet adhesion and aggregation
What is secondary haemostasis?
What does it involve?
stabilisation of the plug with fibrin
involves blood coagulation and the activation of fibrin
What stimulates coagulation?
Tissue factor
What is Von Willebrand factor?
(a blood glycoprotein)
binds to factor VIII
lack of VWF causes thrombosis
What receptors do platelets have on their surface?
Glp1a and thrombin receptors
GlpIIa and GlpIIIb receptos that are available for fibrinogen to bind to
What happens to platelets when they become activated?
- change shape
- change membrane composition (present new or activated proteins on their surface i.e. GlpIIa and GlpIIIb)
What is the life span of a platelet?
around 8 days
What are the 2 initial components of fibrinolysis?
plasminogen and tissue plasminogen activator (tPA)
NOTE: there is normally no interaction between these 2- they interact when a fibrin clot forms
Where is tPA produced?
by endothelial cells
What is the role of tissue plasminogen activator (tPA)?
to convert plasminogen from an inactive zymogen to an active protease (plasmin)
What are the breakdown of a fibrin clot called?
Fibrin Degredation Products (FDP)
NOTE: can be measured for diagnostic purposes and for throbolytic therapy
What is heparin?
What is it used to treat?
an anticoagulant drug that accelerates the action of antithrombin.
It is used for immediate anticoagulation in venous thrombosis and pulmonary embolism
