12.1 The Structure & Function of Platelets

Question 1

What is the main function of platelets?

Answer 1

To aid in the clotting of blood

Question 2

What organelles do platelets contain? Do they contain nuclei?

Answer 2

Platelets contain:
- Granules
- Mitochondria
- Microtubules

They do NOT contain a nucleus.

Question 3

Outline the process of haemostasis in 3 steps

Answer 3

1. Vasoconstriction to reduce blood loss
2. Primary haemostasis (platelet plug formation)
3. Coagulation

Question 4

What is the lifespan of a platelet?

Answer 4

7-10 days

Question 5

List two chemicals that blood vessel endothelium produces to prevent binding of platelets

Answer 5

• Prostacyclin
• Nitric oxide

Question 6

True or false: endothelium promotes fibrinolysis as an anticoagulant measure.

Answer 6

True

Question 7

What are the three steps between inactive platelets and a platelet plug

Answer 7

• Adhesion
• Activation
• Aggregation

Question 8

When a blood vessel is damaged and the endothelial cells are no longer continuous, molecules are exposed that bind to platelets. Give two examples of these

Answer 8

1. Subendothelial collagen
2. Von Willebrand factor

Question 9

Which receptor on platelets binds to Von Willebrand factor?

Answer 9

Glycoprotein 1b

Question 10

Describe the structure of Von Willebrand factor

Answer 10

Long, sticky protein

Question 11

What two types of granules are in a platelet?

Answer 11

• Dense
• Alpha

Question 12

What three processes occur during platelet activation?

Answer 12

• Shape change
• Granule secretion
• Receptor activation

Question 13

What causes platelet activation?

Answer 13

Adhesion to molecules such as collagen and Von Willebrand factor

Question 14

Describe the role of Thromboxane A2 and ADP in platelet activation

Answer 14

• Released by activated platelets
• Activates itself and surrounding platelets

Question 15

Thrombin can activate platelets. How is it produced?

Answer 15

During the coagulation cascade.

Question 16

During autocrine and paracrine activation of platelets, Glycoprotein 2b 3a (GP IIb/IIIa) is produced on the cell surface of platelets. What is it, and what does it do?

Answer 16

• It is a transmembrane fibrinogen receptor
• It binds to fibrinogen and allows aggregation to occur.

Question 17

Platelet coagulation requires platelets to have a negative surface charge. How is this achieved?

Answer 17

Upon platelet activation, anionic phospholipids become exposed on platelet surface.

Question 18

Describe the role of fibrinogen using an oversimplified simile

Answer 18

It is like molecular glue

Question 19

What are some issues that can arise regarding to platelets

Answer 19

• Acute thrombotic events
• Thrombocytopaenia/osis
• Defective platelets

Question 20

Antiplatelet drug indications

Answer 20

• ACS
• TIA/Stroke
• Peripheral arterial disease
• Primary prevention

Question 21

Is aspirin an antiplatelet or an antithrombotic?

Answer 21

Antiplatelet

Question 22

Describe the mechanism of action of aspiring

Answer 22

Inhibits COX-1 enzyme, preventing production of Thromboxane A2 production

Question 23

Mechanism of action of ADP receptor inhibitors as antiplatelet agents

Answer 23

• ADP is used for autocrine and paracrine platelet activation during clotting
• By blocking this receptor, we inhibit the process of clotting

Question 24

Phosphodiesterase inhibitors inhibit platelet aggregation. How?

Answer 24

Nobody knows. Genuinely.

Question 25

List three contraindications for antiplatelet medication

Answer 25

- Active bleeding - Thrombocytopenia - Think twice if they're also on anticoagulants