L13 - Disorders of Blood Coagulation Flashcards
Why do clots form?
To keep blood in
To keep pathogens out
How does clotting occur?
platelets and fibrinogen circulate in the blood.
when here is a damage or rupture to the endothelial wall of blood vessel, primary and secondary haemostasis occur.
Injury causes collagen to come into contact with the blood, which triggers compenents of blood to be activated.
What is primary haemostasis?
platelet adhesion, aggregation, activation
What is secondary haemostasis?
activation of fibrin formation through the clotting cascade
Describe the process of primary haemostasis?
Endothelial cells that line blood vessels store von willebrand factor, and it is released in small amounts continously. If collagen becomes exposed to blood, von willebrand will bind to the collagen. Platelets express the receptors for both von willebrand and collagen, they become activated when binded to them.
Activated platelets are needed to express functional fibrinogen receptors to help aggregation.
Describe what happens in secondary haemostasis?
When damage occurs to blood vessel, a protein called tissue factor (expressed by sub endothelial cells) is exposed.
Tissue factor activates factor 7a, which activates factor 10a. This causes an initial trickle of thrombin
Thrombin activates receptors on platelets, amplifying platelet aggregation, and initiating release of stored von willebrand factor from endothelial cells.
It also releases thromboxanes, ADP. It causes platelets to bind to fibrinogen and convert it to fibrin (its active form)
How is thrombin amplified further?
thrombin activates 2 cofactors: factor 8a and 5a. They form calcium ion dependant complexes with factor 9a (the tenase complex) and 10a (prothrombinase complex) on platelets surface. They in turn increase the production of thrombin
What is Fibrinolysis?
the breaking up of fibrin into smaller fragments
can also be called thrombolysis
How does Fibrinolysis occur?
Plasminogen is activated to plasmin via the tissue plasminogen activator (t-PA).
Plasmin then degrades the fibrin mesh into fragments (called fibrin degradation products) which can be cleared.
What is Anti-thrombin and and what is its function?
it is a serpin - serine protease inhibitor
it is a natural anticoagulant.
When bound to heparan the effects are enhanced.
Describe how protein C and S work as natural anticoagulants?
Protein C is activated by thrombin binding to thrombomodulin on endothelial cells.#
Protein S is an APC cofactor which helps binding on cell surfaces.
They degrade cofactors 5a and 8a
What is Haemophilia?
Failure to clot leading to haemorrhage
What is Thrombophilia?
excessive clotting leading to thrombosis.
What is Disseminated Intravascular Coagulation?
Whole body clots.
Describe Haemophilia A as a bleeding disorder, and where it can it occur?
80% of cases
mutated factor 8a
clotting dosen’t occur normally as there isn’t sufficient amount of thrombin
bleeding into joints, gross swelling from acute haemarthroses
Describe Haemophilia B as a bleeding disorder, and where can it occur?
20% of cases
mutated factor 9a
clotting dosen’t occur normally as thrombin isn’t activated. Increased bleeding
bleeding into joints, gross swelling from acute haemarthroses
Describe von willebrand disease as a bleeding disorder and give example of where it can occur?
Inherited defect/deficiency in vWF.
Without this, platelets can’t go through the process of adhesion, activation and aggregation. As a result there is an increased risk of bleeding.
Affects mucous membranes. Can occur in gums/mouth.
mostly mild but bleeding can vary in severity
Describe factor 5 Leiden mutation as an excessive coagulation disorder?
mutation of factor 5 leads to a resistance of the Protein C inhibition pathway. Causes resistance to APC, and as a result Factor 5a isn’t inactivated
Increases the risk of Deep Vein Thrombosis.
Describe Anti-thrombin deficiency as an excessive coagulation disorder?
Deficiency or mutations within anti-thrombin, then all inhibition pathways are diminished. Nothing to stop clotting.
Increases risk of DVT
Describe Protein C/S deficiency as an excessive coagulation disorder?
Deficiency or mutation in proteins C or S, don’t allow inhibition pathways to work. Nothing to stop clotting
Increases risk of DVT
What factors do development of deep vein thrombosis depend on? Include Virchow’s Triad
Hypercoagulability = alterations to the constituents of blood
Stasis = changes to the normal blood flow
Vessel wall injury = damage to the endothelial layer
What are some signs or symptoms that are associated with Deep Vein Thrombosis?
- pain and tenderness of veins
- limb swelling
- superficial venous tension
- increased skin temperature
- skin discoloration
What happens during Disseminated Intravascular coagulation?
Too much ongoing coagulation, that there is a depletion of clotting factors and platelets before the liver can make more. This leads to bleeding.
Can occur in infection and sepsis, where the body injures its own tissue and organs
What are anti-coagulants and give examples?
They prevent thrombosis/ coagulation from happening.
warfarin (injected), heparin (injected)
Direct oral anticoagulants (oral tablets) that act on specific factors in clotting cascade
