Haematology 2 Platelets

Question 1

Thrombopoiesis

Answer 1

= Platelet production

From megacaryocytes in bone marrow → extend pro platelet shafts into blood stream → release of platelets through budding directly or shaft detaches and platelets detach

Initiated by thrombopoietin

Question 2

Platelet secreted factors

Answer 2

= granule content is released upon activation

alpha-granules: vWF, FV and VIII, PF4, Fibrinogen, PDGF, TGF-alpha

delta (dense)-granules: ADP, Serotonin, Ca2+

TXA2

Question 3

How does Aspirin effect Thromboxan A2?

Answer 3

Aspirin blocks cyclooxyrgenase I which is needed to transform arachidonic acid into TXA2

Question 4

Functions of TX2 and PGI2?

Answer 4

TXA2 = Thromboxan A2 → Vasoconstriction, platelet activation (synthesised by COX 1 - blocked by aspirin)

PGl2 = Prostacyclin → Vasodilation, inactivates platelets (synthesised by COX 2 - blockage only transient as endothelial cells make COX 2)

Question 5

What are microvesicles?

Answer 5

Vesicles produced from platelets, that transport cytoplasmatic proteins and mRNA to other cells

via receptor or endocytosis

Question 6

How do platelets bind to collagen?

Answer 6

Injury → collagen exposed → vWF on collagen binds to vWF-receptor (glycoprotein Ib-V-IX) on platelets → adhesion → activates platelets

stabilised by further adhesion receptors