MoD: Haemostasis and Thrombosis Flashcards
Successful haemostasis depends on…
Vessel wall - arteries, veins and capillaries constrict to limit blood loss.
Platelets - adhere to each other and damaged vessel wall to create a platelet plug.
Summarise the Platelet Release Reaction.
ATP ➡️ ADP
ADP and thromboxane A2 cause platelet aggregation.
5HT and Platelet Factor 3 also released (the latter is important in coagulation.
Platelets fuse after coagulation to help form the platelet plug
Name 3 factors that contribute to control of coagulation.
Thrombin Inhibitors, Endothelium and Fibrinolysis.
How does endothelium contribute to control of coagulation?
Produces anti-thrombotic: Plasminogen activators, Prostacyclin Nitric oxide Thrombomodulin.
Name four thrombin inhibitors that contribute to control of coagulation.
Anti-thrombin III Alpha 1 anti-trypsin Alpha 2 macroglobulin Protein C and S *Thrombin also have negative feedback on Factors 5, 8 and 11*
Outline the actions of Streptokinase
Streptokinase is a plasminogen activator. Causes more plasminogen to be activated to form plasmin. Plasmin is an enzyme that degrades fibrin clots (fibrinolysis). It is used in fibrinolytic therapy (a drastic treatment) e.g. for coronary artery occlusion.
Define haemostasis.
The process that stops bleeding.
Represents a balance between pro-coagulent and anti-coagulent forces.
Define thrombosis.
The formation of a solid mass of blood within the circulatory system.
What are three causes of thrombosis (Virchow’s Triad)? Give examples of each.
Abnormality of blood flow - stagnant, turbulent.
Abnormality of blood vessels - atheroma, direct injury, inflammation.
Abnormality of blood composition - smoker, post-op, post-partum.
What is the appearance of Arterial and Venous thrombi?
Arterial - Pale, granular, lines of Zahr, lower cell content.
Venous - Deep red, gelatinous, soft, higher cell count.
What are the 5 outcomes of thrombosis?
Lysis/Resolution - complete dissolution of thrombus
Propagation - progressive spread of thrombus, Distally in arteries, proximally in veins
Organisation - reparative process
Recanalisation - blood flow re-established but incompletely
Embolism - part of thrombus breaks of travels through blood stream and lodges at distant site.
What are the arterial and venous effects of thrombosis?
Arterial - Ischaemia, infarction, depends on site and collateral circulation
Venous - Ischaemia, infarction, congestion and oedema
Define Embolism.
The blockage of a blood vessel by a solid, liquid or gas at a site distant to its origin.
Name 6 types of embolisms.
Thromboembolism (90%) Nitrogen Medical equipment Tumour cells Amniotic fluid Air
