Platelets; development, morphology & function

Question 1

site & stages of platelet formation

Answer 1

1. megakaryoblast in bone marrow: Hi N:C, lrg round nuclei
2. Promegakaryocyte in bone marrow: lrg cytoplasm w/ blue granules & irregular nuclei
3. Magakaryocyte in bone marrow: blue cytoplasm w/ lobulated nuclei & platelets @ side of cytoplasm
4. Platelet in peripheral blood

Question 2

morphology of platelets

Answer 2

• 1-4 micron
• discoid shape
• cytoplasm pale basophilic

Question 3

a macroplatelet in the blood film indicate…

Answer 3

myeloproliferative neoplasms or increased destruction or inc. platelet turnover

Question 4

What does thromboxan A do?

Answer 4

aggregation of platelets & constricts BV

Question 5

mechanism & effect of apirin?

Answer 5

inhibits cyclooxygenase = impair platelet function = cause bleeding

Question 6

How is a haemostatic plug formed?*

Answer 6

1. vessel injury => exposes Ag on collagen -> platelets stick to Ag via vWf & are activated
2. release seretonin & ADP (dense bodies) = vasoconstrict = dec. blood flow
3. release thromboxane A = platelet agglutination => primary haematostatic plug
   +ve FB loop: plt stick tog. = activate more plt to stick to collagen

Question 7

Thrombocytosis

Answer 7

> 400 x10^9 / L

Question 8

Throbocytopenia

Answer 8

<100 x 10^9 /L

- hemmorrhage due to surgery or trauma