Signals And Processes In Platelet Activation, Adhesion And Aggregation

Question 1

What fascilitates platelet adhesion and activation occur after endothelial injury?

Answer 1

After injury the platelets are exposed to the thrombogenic components of the ECM and the adhesive glycoprotein vWF

Question 2

What is the role of vWF?

Answer 2

It fascilitates platelet adhesion to ECM by acting as a bridge between platelet surface receptors and exposed collagen

Question 3

What do genetic deficiencies of vWF lead to?

Answer 3

Bleeding disorders

Question 4

Which changes occur to the platelets as a result of activation?

Answer 4

• Dramatic shape change: from rounded discs to flat plates with increased surface area
• Appearance of negatively charged phospholipids on their surface: these bind calcium and act as nucleation sites for coagulation factors
• The release of secretory granules

Question 5

Describe the 2 types of secretory granules which platelets contain.

Answer 5

Alpha granules - have P-selectin on their membranes and contain fibrinogen, fibronectin, factor 5 and 8, platelet factor 4, Platelet derived growth factor (PDGF) and transforming growth factor beta

Delta granules- ADP, ATP, ionized Ca++, Histamine, Serotonin and epinephrine

Question 6

When are secretory granules released?

Answer 6

Soon after adhesion

Question 7

What role do ADP and Ca++ play?

Answer 7

ADP - potent activator of platelet aggregation

Ca++ is required for the coagulation cascade

Question 8

The primary hemostatic plug is formed due to which process?

Answer 8

Platelet aggregation

Question 9

How does thrombin stabilize the platelet plug?

Answer 9

It stabilises the plug by activating the coagulation cascade and binding to a protease-activated receptor on the platelet membrane - further promoting platlet aggregation followed by platelet contraction.
Thrombin converts fibrinogen to fibrin, cementing the platelets in their place