1ary Haemostasis

Question 1

What is the goal of 1ary haemostasis?

Answer 1

Form 1ary platelet plug

Question 2

What are the 3 stages of 1ary haemostasis?

Answer 2

1. Platelet adhesion
2. Platelet activation
3. Platelet aggregation

Question 3

What happens upon injury?

Answer 3

1. Vasoconstriction

2. Injury exposes collagen and tissue factor

Question 4

Collagen is highly thrombogenic. What does this mean?

Answer 4

As soon as blood comes into contact with it, it will start to clot (activates platelets)

Question 5

How do platelets bind to subendothelial collagen during injury?

Answer 5

Platelets adhere to exposed collagen through receptors when these encounter exposed thrombogenic sub endothelial matrix proteins

Question 6

Where is vWf secreted from and what is its purpose?

Answer 6

Secreted from endothelial cells and packed into alpha granules inside platelets. It binds tightly to sub endothelial collagen, enabling some platelets to bind

Question 7

Which receptors bind directly to collagen?

Answer 7

GP6 and A2B1

Question 8

Which receptor bind to vWf?

Answer 8

Gp1b-IX-V (indirect collagen receptor)

Question 9

What causes platelets to become activated?

Answer 9

Exposure to collagen (injury)

Question 10

What keeps clotting localised?

Answer 10

1. Platelets can only be activated when exposed to collagen (injury)
2. Coagulation can’t occur without activated platelets

Question 11

Adhesion of platelets to sub endothelial matrix proteins activates platelets and causes what?

Answer 11

1. Change of shape (pseudopodia)

2. Degranulation

Question 12

What is degranulation?

Answer 12

Platelets release granules into blood

Question 13

What do alpha granules contain? What is their purpose?

Answer 13

Help coagulation, aid wound healing

1. Platelet factor 4 (herapin antagonist)
2. Plasminogen activator inhibitor PAI-1
3. Platelet derived growth factor
4. Chemokines

Question 14

What do dense granules contain? What is their purpose?

Answer 14

Help platelet activation (positive feedback)

1. ATP
2. ADP
3. Serotonin
4. Ca2+

Question 15

What do activated platelets secrete?

Answer 15

Thromboxane A2

Question 16

What are functions of thromboxane A2?

Answer 16

1. Acts of smooth muscle cells to cause vasoconstriction
2. Causes more platelets to activate
3. Help with aggregation

Question 17

What is platelet aggregation mediated by?

Answer 17

Fibrinogen

Question 18

What does fibrinogen bind to?

Answer 18

Activated fibrinogen receptor on activated platelets - GP2b/3a

Question 19

What is purpose of fibrinogen?

Answer 19

Links platelets together, forming the primary plug (coagulum)

Question 20

1ary plug can be easily washed away. What step is needed to make this plug stronger?

Answer 20

Coagulation cascade needed which confers fibrinogen into fibrin (very difficult to break down)

Question 21

What is job of fibrin?

Answer 21

Attaches plug to site of injury, keeping it in place

Question 22

P2Y receptors are released from dense granules during degranulation. What is purpose of these receptors?

Answer 22

Receptors for ADP - activate more platelets

Question 23

What is purpose of degranulation?

Answer 23

Increased concentrations of

• Platelet activators
• Coagulation factors
• Vasoconstrictors

Question 24

What drives positive feedback?

Answer 24

Platelets release ADP and thromboxane which recruits more platelets to site of injury

Question 25

What are P2Y receptors sometimes inhibited?

Answer 25

To prevent thrombosis

Question 26

What is the platelet cascade?

Answer 26

Platelets will bind WBCs at site of injury, triggering the inflammatory cascade