MoD Session 5 Flashcards
What does the success of haemostasis depend on?
Vessel wall
Platelets
Coagulation system
Fibrinolytic system
What is haemostasis?
Stopping of haemorrhage within seconds to prevent blood loss
What does a severed artery do in haemostasis?
Contracts to decrease pressure downstream
What happens after 5 minutes of an artery being severed?
Fragile primary haemostatic plug of platelets has formed at mouth of vessel to control bleeding
What happens ~30 minutes after an artery is severed?
Secondary haemostatic plug forms w/fibrin which becomes organised forming granulation tissue which develops into a tiny scar
What do all vessels do to limit blood loss?
Constrict their vessel walls
How is a platelet plug formed?
Platelets adhere to the damaged vessel wall and each other
What is the platelet release reaction?
ATP –> ADP
ADP and thromboxane A2 cause platelet aggregation
5HT and platelet factor 3 released
Which molecules are important in platelet coagulation?
5HT
Platelet factor 3
What do platelets do after aggregation?
Coalesce
Where are the factors used in the intrinsic coagulation system found?
Within BV
What is needed to activate the extrinsic coagulation system?
Exo-BV factors
Which factors are activated in the intrinsic coagulation system?
12a –> 11a –> 9a –> 10a
Which factors are activated in the extrinsic coagulation system?
3a –> 7a –> 10a
How does activation of factor 10a by both the extrinsic and intrinsic coagulation systems cause fibrin formation?
10a –> thrombinogen –> thrombin –> fibrinogen –> fibrin
Why does the coagulation system have to be tightly regulated?
There is enough thrombin in 1 ml of blood to convert all the fibrinogen in the body to fibrin
How is the coagulation system tightly regulated?
Balance procoagulant and anticoagulant forces
What can inhibit the activation of fibrinogen by thrombin?
Anti-thrombin III
Alpha 1 antitrypsin
Alpha 2 macroglobin
Protein C and S
What are the effects of inherited antithrombin III or protein C and S deficiencies?
Thrombosis (thrombophilia)
What is the fibrinolytic system?
Conversion of plasminogen to plasmin which can dissolve fibrin
Give two examples of widely used fibrinolytic therapies.
Streptokinase A
Tissue plasminogen activator (tPA)
What is needed for the fibrinolytic system to function?
Plasminogen activators
What is activated partial thromboplastin time (aPTT)?
Time taken to generate fibrin from initiation of the intrinsic pathway
When is aPTT long?
Haemophilia A and B
Factor deficiencies
How do you test aPTT?
Activate factor XII w/out activating factor VII in phospholipid emulsion
What is prothrombin time (PT)?
Time taken to generate fibrin from factor VII
How do you test PT?
Add thromboplastin, recalcify and wait for fibrin filaments to form
When is PT long?
Inherited factor VII deficiency
Liver disease
Warfarin treatment
Sever bleeding/massive transfusion
How is a long PT rectified in severe bleeding/massive transfusion?
1:1 mix w/normal plasma
What is thrombin time (TT)?
Time taken for fibrinogen –> fibrin in the presence of thrombin
How is TT measured?
Add thrombin and calcium and wait for fibrin filaments to form
When is a long TT seen?
Deficient fibrinogen
Abnormal fibrinogen
Presence of inhibitor to reaction
What does the endothelium secrete?
Anti-thrombotic molecules e.g. Plasminogen activators, prostacyclin, nitric oxide and thrombomodulin
What is thrombosis?
Formation of a solid mass of blood w/in circulatory system
What does thrombosis occur due to?
Virchow’s triad
What is Virchow’s triad?
Abnormalities of:
Vessel wall
Blood flow
Blood components
What can cause abnormalities of the vessel wall?
Atheroma
Direct injury
Inflammation
What can cause abnormalities of blood flow?
Stagnation
Turbulence
In what circumstances might a patient be hyper-coaguable?
Smoker
Post-partum
Post-op
Why can patients who are post-partum have abnormalities of blood components?
Due to over-enthusiastic response to blood loss from childbirth
What is given post-op to reduce the risk of abnormalities of blood components causing hyper-coaguability?
Prophylactic treatment
How do arterial thrombi appear?
Granular
Pale
Low cell content
Lines of Zahn due to bloodflow - yellow = fibrinous, red = RBCs
How do venous thrombi appear?
High cell content
Gelatinous
Deep red
Soft
What are the possible outcomes of thrombosis?
Lysis Propagation Organisation Recanalisation Embolism
Why is lysis the best outcome of thrombosis?
Fibrinolytic system is active so can completely dissolute thrombus to re-establish blood flow
When is lysis the most likely outcome of thrombosis?
When thrombi are small
What can aid lysis of a thrombus and help return bloodflow to an ischaemic area?
Streptokinase A
Why is propagation when an outcome of thrombosis?
Progressive spread of thrombosis which is distal in arteries and proximal in veins
How does a thrombus change as it moves during propagation?
Increases in size with increasing venous diameter
What is organisation as an outcome of thrombosis?
Reparative process where ingrowth of fibroblasts and capillaries keep lumen unobstructed
What process is organisation as a result of thrombosis like?
Formation of granulation tissue
What is recanalisation?
One or more channels formed through organising thrombus which re-establish blood flow
Is previous bloodflow usually matched after recanalisation?
No, recanalisation is usually incomplete
What is embolism as an outcome of thrombosis?
Where part of the thrombus breaks off and travels through bloodstream to a distant site