Haemostasis, thrombosis and associated therapies

Question 1

What is haemostasis?

Answer 1

Arrest of blood loss from damaged vessels

Question 2

What is a summary of what occurs in haemstasis?

Answer 2

Platelets are non adhesive and circulate singly. During vessel wall injury platelets aggregate. become stabilised by fibrin and arrest bleeding from several vessels.

Question 3

What chemical stops platelet activation? How?

Answer 3

Nitric oxide

It causes vasodilation on blood capillaries

Question 4

Explain how aggregation of platelets and vasoconstrictions occurs

Answer 4

• Damage to blood vessel
• Exposure of platelets to collagen and vWF in the extracellular matrix and later exposure to thrombin
• Platelets activate and adhere
• Release of mediators
• Vasoconstriction + aggregation of platelets
• Formation of a soft platelet plug

Question 5

What happens during primary haemostasis and the clotting pathway?

Answer 5

PH = the cellular phase of haemostasis.
Platelets move towards the matrix. This then sticks and is activated by binding to either collagen or vWF. This activated the platelets which then activate fibrinogen (they connect to platelets via fibrinogen attachments).

Clotting pathway
Initiation - activated by Tissue Factor (made when the endothelium is damaged). This takes place on TF expressing cells in tissues after blood, with its clotting factors, leaks out the blood vessel.
Amplification = initiated by thrombin. and involves activation of many factors including FV, FVII, FX.
It takes place on activated platelets.

Question 6

What are the two main features of a stable clot?

Answer 6

Fibrin and platelets

Question 7

Explain arterial thrombosis

Answer 7

• usually associated with artherosclerosis (plaque building up around the arteries)
• form at site of vascular injury
• large platelet formation

Question 8

Explain venous thrombosis

Answer 8

• associated with turbulent flow of blood or vascular injury following surgery/trauma
• platelet component, large fibrin component
• red blood cell component

Question 9

What is important about drugs given for thrombosis?

Answer 9

The treatment is a balancing act. This is between clot formation and the risk of haemorrhage.

Question 10

Give details on aspirin on blood clot formation

Answer 10

It is a platelet agonist, vasoconstrictor.
Major component of platelet COX-1
Low dose of aspirin - irreversible inhibition of cox-1

Question 11

What does P2Y12 receptor antagonists do to cells and clot formation?

Answer 11

ADP stimulation of cells

This causes irreversible clot formation.