Haemostasis and Thrombosis

Question 1

What is the difference between intrinsic and extrinsic clotting mechanism?

Answer 1

. Intrinsic occurs when a blood vessel wall is damaged and collagen is exposed (detected as foreign surface)
. Extrinsic occurs when damaged tissues release thromboplastin

Question 2

Describe how the extrinsic and intrinsic pathways converge to eventually result in the formation of a clot.

Answer 2

. Extrinsic- damaged tissues release thromboplastin
. Intrinsic- damaged blood vessel exposes collagen (foreign surface), which releases clotting factors

. Thromboplastin and clotting factors activate factor X
. Activated factor X activates prothrombin to be converted to thrombin
. Thrombin activates fibrinogen to be converted to fibrin
. Fibrin combines with platelets to form clot

. This is an amplification pathway

Question 3

What happens in the platelet adhesion reaction?

Answer 3

. Platelets adhere to endothelial cells in damaged blood vessels, facilitated by von Willebrand’s factor
. Release of 5HT, ADP, and thromboxane
. 5HT causes vasoconstriction to slow blood loss

Question 4

What happens in the platelet aggregation reaction?

Answer 4

. ADP and thromboxane cause other platelets to clump together, facilitated by glycoprotein IIb, IIIa, and von Willebrand’s factor
. Fibrin (from coagulation cascade) and platelets clump together to form clot

Question 5

What does a higher INR suggest?

Answer 5

Blood takes longer to clot, so suggest liver disease (not able to produce vitamin K, which is involved in producing clotting factors), or person may be on anticoagulants

Question 6

Is venous thrombosis more related to the coagulation cascade or platelets? How about arterial thrombosis?

Answer 6

. Venous thrombosis (e.g. DVTs) is more of a coagulation factor event
. Arterial thrombosis (i.e. leading to myocardial infarctions and ischaemic strokes) is more of a platelet event

Question 7

What is haemophilia A? What are the risks of this condition?

Answer 7

. Condition that leads to low levels of factor VII in clotting cascade
. Individual is at risk of haemorrhage and prolonged bleeding

Question 8

How do you treat haemophilia A?

Answer 8

. Treat with factor VIII from blood donors on regular basis or…
. Spray ADH up nose to promote release of coagulation factors

Question 9

What is haemophilia B?

Answer 9

Same as haemophilia A but with low levels of factor IX

Question 10

What is purpura?

Answer 10

Spontaneous skin bleeding