Haemostasis

Question 1

What is haemostasis?

Answer 1

The body’s reaction to injury or bleeding, formations of blood clots to prevent blood loss

Question 2

What are the stages of haemostasis?

Answer 2

1. Contraction of the blood vessel
2. Unstable platelet plug formation (primary)
3. Stabilisation of unstable platelet plug (secondary)

Question 3

What 2 glycoproteins does platelet plasma membrane contain?

Answer 3

GP1a and GP1b

Question 4

How do GP1a and GP1b work in forming a platelet plug?

Answer 4

When a vessel is damaged the GP1a can bind to the wall directly
GP1b binds to circulating von Willebrand factor which then binds to the wall of the damaged vessel

Question 5

What physical change occurs when platelets use their glycoproteins to bind to the vessel wall or VWF and why?

Answer 5

They change from a disc shape to a more spherical shape with spicules, which help the platelets clump and form an unstable platelet plug
They also release the contents of their storage granules

Question 6

What granules are present in platelets?

Answer 6

Alpha-granules and dense-granules

Question 7

What is contained in the granules within platelets?

Answer 7

ADP, fibrinogen and VWF

Question 8

How do the granules get released?

Answer 8

The platelet membrane invaginates, forming a passage to the surface of the cell

Question 9

How does vasoconstriction occur in the first stage of haemostasis?

Answer 9

Arachidonic acid fromt eh membrane of the platelets is used to produce thromboxane A2, a vasoconstrictor

Question 10

What does the release of ADP and thromboxane cause?

Answer 10

It causes a positive feedback loop, alongside thromboxane A2, which stimulates platelet activation and aggregation
The ADP binds to P2Y12 and thromboxane A2 to the thromboxane A2 receptor which causes the GP2b/3a receptor to change shape and become capable of binding to fibrinogen

Question 11

What happens when fibrinogen binds to the activated GP2b/3a?

Answer 11

This further causes platelets to link together due to them binding to fibrinogen (primary haemostasis)

Question 12

What does prostacyclin do?

Answer 12

It causes vasodilation and suppresses platelet activation, stopping them from aggregating when the blood doesnt need to clot

Question 13

What does aspirin do?

Answer 13

Irreversibly inhibits the cyclo-oxegenase(COX) enzyme required for the production of thromboxane A2, therefore prevents platelet aggregation

Question 14

Which factor does VWF carry?

Answer 14

Factor VIII

Question 15

How is a unstable platelet plug stabilised?

Answer 15

1. Blood coagulation produces thrombin

2. Thrombin cleaves fibrinogen to form a fibrin clot, stabilising the platelet plug

Question 16

What clotting factors arent produced by the liver?

Answer 16

Factor VIII and VWF

Question 17

Which clotting factors require vitamin K to become activated?

Answer 17

Factors II, VII, IX, X

Question 18

Where do clotting factors work?

Answer 18

On the phospholipid membrane of platelets

Question 19

How does Heparin work?

Answer 19

It indirectly helps antithrombin work better so antithrombin can inactivate factors Xa and IIa(thrombin) quicker. Can be given intravenously or subcutaneously

Question 20

How does Warfarin work?

Answer 20

It is a vitamin K antagonist so stops factors II, VII, IX, X from becoming functional. Taken orally, taken in emergency as no need to monitor

Question 21

How do direct oral anticoagulants work?

Answer 21

They directly inhibit IIa or Xa

Question 22

How does flibrinolysis occur?

Answer 22

Tissue plasminogen activator(t-PA) and plasminogen come together on the clot by binding to fibrin, then plasminogen is converted to plasmin which breaks down fibrin to form Fibrin-degradation products

Question 23

What does tranexamic acid do?

Answer 23

Binds to plasminogen preventing it from binding to fibrin so it cannot convert into plasmin = no fibrinolysis

Question 24

What is thrombosis?

Answer 24

The formation of a clot in a stable vessel

Question 25

What factors contribute to thrombosis?

Answer 25

• Something wrong with the components of blood
• Something wrong with the vessel wall
• How blood is flowing