Haemostasis

Question 1

In tact endothelium expresses which:

• anticoagulants [3]
• platelet inhibitors [2]
• which substance which metabolises ADP? [1]

Answer 1

In tact Endothelium expresses:

Anticoagulants:

• Tissue factor pathway inhibitor (TFPI)
• Thrombomodulin
• Heparin-like proteoglycan

Ectonucleotidase - metabolise ADP - which activates platelets

Platelet inhibitors
Nitric oxide
Prostacyclin

Question 2

How does platelet activation occur?

Question 3

Explain the three stages of haemostasis

Answer 3

Primary hemostasis:
Blood vessel contraction /vasoconstriction
Platelet plug formation upon platelet adhesion and aggregation

Secondary hemostasis:
Activation of the coagulation cascade
Deposition and stabilization of fibrin - mesh of fibrin

Tertiary hemostasis
Dissolution of fibrin clot
Dependent on plasminogen activation

Question 4

Haemostasis - see her slides

Answer 4

1. Vasoconstriction: reduces blood flow & loss
2. Activation of processes that lead to activation of platelet clot
3. Tissue factor also released that causes

Question 5

What causes vascular constriction when trauma to vessel wall occurs? [3]

Answer 5

• Local myogenic spasm – caused be Ca2+ release
• Endothelium in injured vessel wall and platelets release vasoconstrictor substances such as Endothelin, serotonin and Thromboxane A2 (TBA2)
• Nervous reflexes

BUT doesnt completely stop bleeding

Question 6

Which parts of platelet structure help with its role in clotting? [4]

Answer 6

The platelet membrane
•surface for the assembly of activated coagulation cascade during secondary hemostasis.
•Glycoproteins play role in platelet plug formation

ẟ dense granules: ADP & serotonin
•Facilitate platelet adhesion and vasoconstriction in the area of the injured vessel

alpha-granules
•Play an important role in the initial phase of vessel repair, blood coagulation, and platelet aggregation. vWF, fibrinogen, factor V, platelet derived growth factor, high molecular weight

•Platelet contractile proteins
Play a role in platelet activation, aggregation and clot retraction

Question 7

Platelet adhesion

Question 8

What is the role of vWF? [2]

•Deficiency of vWf will which type of haemostasis? [2]

Answer 8

• Glues / bridges adjacent platelets together due to bridge between specific glycoproteins on the surface of platelets and collagen fibres
• complexed with factor VIII and prevents factor VIII’s degradation (if factor VIII becomes degraded it effects secondary haemostasis)

•Deficiency of vWf will affect both primary and secondary haemostasis

Question 9

How does blood clot occur?

What are the two pathways for formation of thrombin? [2]

Answer 9

Formation of thrombin:

Extrinsic pathway —> Activated factor X (Xa) —> Common Pathway –> Thrombin
Intrinsic pathway —> Activated factor X (Xa) —> Common Pathway –> Thrombin

Thrombin activates fibrinogen to fibrin

Question 10

What is haemophilia A?
What is haemophilia B?

Answer 10

• Haemophila A (FVIII)
• Haemophilia B (FIX)

X-linked recessive