First Aid, Chapter 2 Cells Involved in Immune Responses, Platelets

Question 1

What is the general primary role of platelets?

Answer 1

homeostasis

Question 2

How big are platelets? What are they derived from? What is the lifespan?

Answer 2

• Anucleated cells that are 2–3 μm in diameter (Figure 2-11).
• Derived from megakaryocyte precursor (Figure 2-3).
• Average life span is 8–12 days.

Question 3

What is the formation of platelets mediated by? What surface receptors do they express?

Answer 3

• Formation regulated by thrombopoietin secreted by the liver and kidney.
• Express surface receptors for IgG and CD23.

Question 4

What are the functions of platelets?

Answer 4

-Thrombus formation (Figure 2-12).
o After endothelial damage, platelets are activated by exposed collagen and von Willebrand factor (vWF).
o Activated platelets release contents of granules (ADP/ATP, calcium, serotonin, TGFβ, platelet factor 4 (PF4), platelet-derived growth factor (PDGF), vWF, and fibrinogen).
o Arachidonic acid pathway initiated to produce thromboxane A2, which activates more platelets.
o Platelets clump together via fibrinogen and vWF interaction with the GPIIb/IIIa receptor
-Cytokine release

Question 5

What is Wiskott-Aldrich syndrome? What is the inheritance? What is it characterized by? What is the defective gene?

Answer 5

Wiskott-Aldrich syndrome is an X-linked disorder characterized by eczema, infections, and thrombocytopenia (as well as small platelet volume). The defective gene encodes for the Wiskott-Aldrich syndrome protein (WASp) used in cell signaling

Question 6

What are diseases with thrombocytopenia or reduced platelet function?

Answer 6

o Aplastic anemia o Bernard-Soulier syndrome
o Drug-induced thrombocytopenia
o Gaucher’s disease
o Glanzmann’s thrombasthenia
o HELLP syndrome
o Hemophilia
o Hermansky-Pudlak syndrome
o Wiskott-Aldrich syndrome
o Idiopathic thrombocytopenic purpura (ITP) (due to antibodies to platelet’s GP2b3a) o Thrombotic thrombocytopenic purpura (TTP) (due to antibodies to ADAMTS13)
o Von Willebrand disease
o Heparin-induced thrombocytopenia (due to antibodies to PF4)

Question 7

In which platelet disorder are platelets abnormally large? Hint: Antibodies to platelet’s GP2b3a are also seen.

Answer 7

ITP