Disorders of primary hemostasis

Question 1

Primary hemostasis step 1

Answer 1

Vasoconstriction mediated by neural stimulation and endothelin released from endothelial cells

Question 2

Primary hemostasis step 2, details

Answer 2

Platelet adhesion

vWF binds subendothelial collagen, then platelets bind vWF via GP1b

Question 3

Where does vWF come from?

Answer 3

Weibel-Palade bodies of endothelial cells and alpha granules of platelets

Question 4

Primary hemostasis step 3, details

Answer 4

Platelets release ADP which promotoes expsoure of GPIIb/IIIa receptor on platelets, and TXA2 which promotes platelet aggregation

Question 5

Primary hemostasis step 4

Answer 5

platelets aggregate via GPIIb/IIIa using fibrinogen as linker

Question 6

Pathophys of immune thrombocytopenic purpura (ITP)

Answer 6

igG Autoantibodies formed against platelet antigens (GPIIb/IIIa) and consumed by splenic macrophages –> thrombocytopenia

Question 7

Acute form of ITP

Answer 7

Seen in children after viral illness, self limited

Question 8

Chronic form of ITP

Answer 8

Seen in women of childbearing age, may be secondary to SLE. Can cause short-lived thrombocytopenia in neonates as IgG antibodies cross placenta

Question 9

lab findings of ITP

Answer 9

decreased platelet count
increased megakaryocytes
normal PT/PTT

Question 10

treatment of ITP

Answer 10

IVIG
Corticosteroids
Splenectomy

Question 11

Two types of microangiopathic hemolytic anemia

Answer 11

TTP and HUS

Question 12

TTP pathophys

Answer 12

Antibodies produced against ADAMTS13 which normally cleaves vWF into small monomers
Abnormal platelets lead to microthrombi

Question 13

HUS pathophys

Answer 13

Due to endothelial damage or drugs. Seen in O157:E7 infection in children – > verotoxin damages endothelium –> platelet microthrombi

Question 14

findings in HUS and TTP

Answer 14

schisocytes 
hemolytic anemia
renal insufficiency (HUS)
neurological symptoms (TTP)
increased megakaryocytes

Question 15

Treatment of TTP and HUS

Answer 15

Corticosteroids and plasmapheresis

Question 16

Name and describe the qualitative platelet disorders

Answer 16

Bernard-Soulier syndrome - genetic GPIb deficiency
Glanzmann thromasthenia - genetic GPIIb/IIIa deficiency
Aspirin - inactive COX prevents TXA2 from promoting platelet aggregation
Uremia -disrupts adhesion and aggregation of platelets