Haemostasis - 2 Flashcards
What do platelets provide for coagulation?
Phospholipids
What converts fibrinogen to fibrin?
Thrombin
What is the main source of coagulation factors?
Liver mainly
Endothelium and megakaryocytes - vWF
What coagulation factors must bind to Ca2+ to achieve full functional activity permit attachment to activated platelet surfaces?
Factors II, VII, IX and X
Two coagulation inhibitors - Protein C and S
What is needed to add Ca2+ binding sites to 6 coagulation factors and inhibitors?
Vitamin K
What provides the structural strength for the haemostatic plug and anchors the plug to adjacent tissues?
Fibrin
Name the three main inhibitors of blood coagulation.
Antithrombin
Protein Ca
Protein S
What is the key message about haemostasis?
Blood coagulation is a balance
Need activation and anticoagulants
What does activation of blood coagulation and anticoagulatants do?
Activation - triggers coagulation
Anticoagulants are needed to stop coagulation. The right amounts of coagulants and anticoagulants are needed for effective haemostasis.
What happens if there is too little coagulation?
Bleeding risk
What happens if there is too little anticoagulation or too much coagulation?
Thrombosis risk (clotting inside blood vessels)
What is fibrinolysis?
Clears fibrin from normal blood vessels
Name the activators of fibrinolysis.
tPA
Urokinase
Name the inhibitors of fibrinolysis
Plasminogen Activator Inhibitor (PAI)
Antiplasmin
Describe how clot lysis occurs.
Both plasminogen and tPA can bind to fibrin.
If large amounts of tPA are present, when a clot is forming the tPA will also bind to fibrin and activate plasminogen.
Clot lysis will occur
Where is the most important place for fibrinolysis to occur?
In veins
Why is fibrinolysis not as important in arteries than in veins?
Fast blood flow carries activating coagulation factors (and fibrinolytic) factors away from the site of platelet activation
Describe the normal blood flow and platelet relationships.
Platelets are normally unable to adhere to the smooth surface of the endothelium.
Endothelial ADPase clears ADP from activated platelets.
NO secreted
PGI2 produced
What is the function of NO?
Dilates vessels, inhibits platelet activation
What is the function of PGI2?
Dilates blood vessels, inhibits platelet activation
What inhibits platelet activation?
NO
PGI2
Describe the normal velocity of blood flow and the results of it.
Velocity of flow is faster in the centre of blood vessels due to shear stress at the endothelial cell surface.
This results in a central red cell rich zone
Plasma and platelet rich zone is adjacent to the endothelium.
What happens in injury to the endothelium?
P-selectin is expressed: platelets may adhere
Endothelin produced by adjacent endothelium - produces vasoconstriction.
