How are platelets released into peripheral circulation from the ...

[laurencescou]

How are platelets released into peripheral circulation from the bone marrow?
 
  a. Mature platelets squeeze between sinusoid endothelial cells.
  b. Megakaryocyte cytoplasmic fragments extend through the endothelial cells, lining the sinusoids, into blood and then shed platelets.
  c. Platelets adhere to white cells and exit with them.
  d. Megakaryocytes exit the marrow with white cells and then platelets fragment off once they reach the blood.

Question 2

When platelets are activated, all of the following occur except:
 
  a. a-Granule contents are released.
  b. Smooth cytoplasmic membrane margins change to spiny projections.
  c. The prostaglandin (eicosanoid synthesis) pathway is activated.
  d. Adenosine diphosphate (ADP) release is inhibited.

[bigcheese9]

Answer to Question 1

ANS: B
Cytoplasmic extensions elongate and pierce between the endothelial cells that line the marrow sinuses; then they extend into venous blood. These extensions release platelets once they enter blood. The cytoplasmic extensions are called proplatelet processes.

Answer to Question 2

ANS: D
When the platelet is activated, storage ADP is released from the platelet and then binds to its ligand on the platelet membrane, acting as an agonist. All the other changes listed do occur when the platelet is activated.