Lecture 9 - Haematology II (Haemostasis)

Question 1

Define Haemostasis

Answer 1

The process of clotting to prevent blood loss after an injury

Question 2

Name the three phases of haemostasis

Answer 2

Vasoconstriction; Platelet Adhesion + Aggregation; Coagulation Phase (+ Formation of a Stable Haemostatic Plug)

Question 3

What is the insoluble end-product of the coagulation phase?

Answer 3

Fibrin

Question 4

Describe the steps of the Extrinsic Pathway of Coagulation

Answer 4

1 - Tissue factor is released from the endothelial lining into the blood (due to damage to lining)
2 - Tissue factor combines with Clotting Factor VII to form Factor VIIa-Tissue Factor Complex
3 - The Complex then combines with Factor X (which becomes Factor Xa)

Question 5

Describe the steps of the Intrinsic Pathway of Coagulation

Answer 5

Note: this pathway is activated by proenzymes (usually Factor XII) that respond to exposed collagen

1 - Some Factor IX (which has been activated by the Extrinsic Pathway) feeds into the Intrinsic Pathway
2 - Factor IX combines with its co-factor, Factor VIII, to form the Factor X-activating complex
3 - This pathway activates Factor X again (slower but more efficient than the Extrinsic Pathway)

Question 6

Describe the steps of the Common Pathway of Coagulation

Answer 6

1 - Factor Xa combines with its co-factor, Factor Va, to form Prothrombinase
2 - Prothrombinase activates Prothrombin to Thrombin
3 - Thrombin activates Fibrinogen to Fibrin (which forms the stable haemostatic plug)

Question 7

What two substances are required for Haemostasis?

Answer 7

Calcium (Ca2+) and Vitamin K

Question 8

What substances limit/control clotting?

Answer 8

Anticoagulents (e.g., Antithrombin and Heparin)

Question 9

What process (and enzyme) prevent a clot from remaining in the body and impairing circulation?

Answer 9

Fibrinolysis - the enzyme Plasmin breaks down Fibrin into degradation products