Haemostasis

Question 1

What are the general principles of haemostasis?

Answer 1

To prevent bleeding and prevent unnecessary coagulation, allowing blood to flow§

Question 2

Describe the response to vascular injury

Answer 2

• platelet-collagen adhesion
• platelet aggregation
• fibrinogen attaches and

Question 3

How are platelets formed?

Answer 3

• Megakaryocytes produce platelets in the bone marrow
• Platelets ‘bud’ from cytoplasm
• Normal life span is 7-10 days (anti platelet drugs must be stopped 7-10 days before surgery)

Question 4

How do platelets adhere to vessels?

Answer 4

Damage to vessel wall
•Exposure of underlying tissues
•Platelets adhere to collagen via vWF/receptor

Question 5

Once initial platelets have attached to vessel walls, how do platelets aggregate?

Answer 5

• Secrete ADP, thromboxane and other substances to become activated and activate other platelets
• Involved in activation of the clotting cascade
• Provide some coagulation factors by secretion from internal stores
• Finally, they aggregate by cross linking of platelets to form a platelet plug

Question 6

Outline some targets for anti-platelet drugs

Answer 6

• Plt receptors –glycoprotein complexes e.g.
GP1b-V-IX, GPIIb-IIIa 
• Von willebrands factor 
• Fibrinogen 
• Collagen 
• ADP 
• Thromboxane/arachidonic acid 
• Thrombin

Question 7

What is the blood clotting cascade?

Answer 7

Amplification system activation of precursor proteins to
generate thrombin (IIa) 

• Thrombin converts soluble fibrinogen into insoluble fibrin
• which enmeshes initial platelet plug to make stable clot

It is controlled by:

–Natural anticoagulants to inhibit activation
–Clot destroying proteins which are activated by the clotting

Question 8

How is the blood clotting cascade initiated?

Answer 8

-

Question 9

What is the role of Von Willebrand’s factor in blood clotting cascade?

Answer 9

Involved in platelet adhesion to the vessel

wall, platelet aggregation, and also carries FVIII

Question 10

What role does the vessel wall play in the blood clotting cascade?

Answer 10

• Vasoconstriction

• Production of  Von Willebrandsfactor
(vWF)
–Essential for platelet adhesion
–Carrier and ‘protector’ of Factor 8
(clotting protein) 

• Exposure of collagen and Tissue factor
which initiates activation of clotting factors (proteins)