Thromboembolism

Question 1

Haemostasis

Answer 1

process of stopping bleeding from a blood vessel and has three parts :
- vascular spasm
- formation of platelet plug
- blood coagulation

Question 2

Vascular spasm

Answer 2

Vasoconstriction means to reduce the blood flow
- direct injury to vascular smooth muscle
- chemicals released by endothelial cells and platelets
- reflexes initiated by local pain receptors

Question 3

Platelet plug formulation

Answer 3

normal situation = platelets do not stick to each other or smooth muscle as they release nitric oxide and prostacyclin.

damaged endothelium
- collagen fibres exposed
- von willebran factor adheres
- activation of platelets - release of ADP and thromboxane A2

Functions of platelet plug formation :
- seals the break in the vessel
- action myosin complex within the aggregated platelets contracts to compact and strengthen the initial loose plug
- releases vasoconstrictors that reinforce the initial vascular spasm
- releases other mediators that enhance blood coagulation which is the next step of haemostasis

Question 4

Blood coagulation/ clotting

Answer 4

• transformation of blood from a liquid into a solid gel
• most powerful haemostasis mechanism
• final step = fibrinogen ( soluble ) and fibrin ( insoluble )

Thrombin converts fibrinogen into fibrin. This activate factor13 ( fibrin stabilising factor ) to stabilise fibrin mesh. This induces its own formation and enhances platelet aggregation

Clotting cascade :
- calcium
- platelet factor 3
- vitamin k
- intrinsic and extrinsic pathway

Question 5

Clotting cascade - intrinsic pathway

Answer 5

• occurs when Hageman factor ( factor 12 ) comes into contact with for example exposed collagen. Activation of factor 7 leads to activation of factor 12. This then leads to activation of factor 11 and then factor 9 and then factor LOOK AT DIAGRAM

Question 6

Clotting cascade - extrinsic pathway

Answer 6

• tissue thromboplastin directly activates factor 10. This means it skips all the steps in comparison to the intrinsic pathway. Both intrinsic and extrinsic pathways are identical from factor 10 onwards

Question 7

Prevention of inappropriate clot formation

Answer 7

• remove clotting factors
• inhibition of activated clotting factors
• antithrombin III
• Protein C
• Heparin
• Tissue plasminogen activator