Haemostasis and anticoagulants Flashcards
Define haemostasis
Haemostasis: functions to limit blood loss following vascular damage yet without compromising fluidity of blood
Define thrombosis
Thrombosis: Occlusion of a blood vessel due to intravascular blood clot or platelet clump
What mechanisms normally suppress blood coagulation and platelet activation
Non-thrombogenic surface of the endothelium
Production of Nitric Oxide and Prostacyclin by the endothelium - this inhibits platelet aggregation
Presence of natural anti-coagulants in the blood e.g. antithrombin III
What can deficiency of a clotting factor lead to?
Uncontrollable bleeding
Briefly explain the process of Haemostasis and platelet plug formation
Wound occurs:
smooth muscle vasospasm to constrict blood flow to the area.
Sub endothelial collagen is exposed to blood. Platelets adhere to the collagen and aggregate. They change shape and pseudopodia (finger-like extensions) allows them to stick to one another.
They also release chemicals from their granules. These include:
Serotonin (vasoconstriction)
Thromboxane A2 (Vasoconstriction and platted aggregation)
ADP (Platelet aggregation)
Platelets clump together to seal the area forms a platelet plug
what are coagulation factors?
Plasma proteins made by the liver that circulate in their inactive form and are activated by proteolytic cleavage to become active proteases and initiate the next step in the cascade.
What initiates the intrinsic pathway and Briefly mention the clotting factors involve in the intrinsic pathway?
Contact of blood with Exposed sub endothelial collagen fibres.
Factor 12, 11, 9, (8 assists activation of) 10.
What initiates the extrinsic pathway and Briefly mention the clotting factors involve in the extrinsic pathway?
Tissue damage Tissue factor (F3), 7, 10
Describe the common coagulation pathway
Factor 10 (prothrombinase) converts prothrombin into thrombin. THROMBIN converts fibrinogen intro fibrin which stabilises the clot and strengthens it.
what does the fibrinolytic system do?
it is a physiological repair system which dissolves blood clots.
What enzyme is involved in dissolving blood clots, what does it do and how is it made?
Plasmin. It breaks down fibrin in the clot to soluble degradation products.
Tissue Plasminogen factor converts plasminogen to plasmin
What are two types of inappropriate activation of the coagulation cascade?
Venous thrombosis
Arterial thrombosis
Describe the mechanism of venous thrombosis and how can this be dangerous
Intravascular blood clots which form in deep veins, particularly in the legs where blood flow is slow.
This can be dangerous if the clot breaks off and and circulates as it can block finer blood vessels e.g. usually pulmonary arteries.
Describe the mechanism of arterial thrombosis
Platelets aggregate (white), usually due to rupture of atherosclerotic plaque and then encapsulated by clot (red)
What are the common sites of arterial thrombosis and what do they lead to?
Cerebral artery: thrombotic stroke
Coronary artery: myocardial infarction
what is the treatment of venous thrombosis?
anticoagulant drugs