Platelet Structure and Function

Question 1

Platelets are derived from

Answer 1

megakaryocytes of the myeloid lineage

CFU-EMk stimulated to become megakaryocyte via TPO (thrombopoietin)

Question 2

Old platelets are removed by

Answer 2

the spleen and by kupffer cells in the liver

Question 3

Platelet Surface receptors and function

Answer 3

VWF R: ligand that facilitates adhession
Fibrinogen R: adhesive ligand
ADP R: responsible for platelet shape and aggregation
Thrombin R: activates platelets trough unique protease-activate receptors (PARs)

Question 4

Platelet Activation

Answer 4

Injury to endothelial cell makes it present VWF and exposed collagen
VWF is also a carrier for factor VIII
vWF is glue between platelet and subendothelium

Question 5

Order of platelet activation

Answer 5

Shape Change
Granule Release
Phospholipid Exposure
Specific Receptor exposure
* Receptors are only active once fibrinogen and vWF have bound

Question 6

Specific Receptors

Answer 6

glycoprotein IIb, IIa

Question 7

Granules

Answer 7

Dense granules: can’t see with light micro

• ATP/ADP
• Serotonin
• Calcium

Alpha Granules: visible with light micro

• Growth factors PDGF, TGF-beta
• Platelet factor 4
• vWF

Question 8

Phospholipid exposure

Answer 8

Platelet activation results in the scramblase-mediated transport of negatively charged phospholids to platelet surface.

Question 9

Platelet Aggregation

Answer 9

Cluster of platelets

come together via IIb/IIIa receptor via binding of vWF or Fibrinogen

Question 10

How do platelets promote vessel repair?

Answer 10

Platelets release growth factors like PDGF, TGF-beta
Fibroblast GF
Insulin like GF
VEGF