Hematopoietic stem cells are formed in the bone marrow. All blood cells originate from them. Platelets are produced by megakaryocytes entering blood vessels.
Therefore, blood flow is essential for the formation of FUNCTIONAL platelets.
Platelets are key players in hemostasis and thrombosis; bleeding accompanies low numbers of circulating platelets. The first response to an injury of a blood vessel is platelet adhesion to it, followed by platelet activation in response to agents produced at vascular lesions. Then platelets release numerous activators that amplify activation of other platelets and contribute to platelet aggregation and thrombus stability.
Once platelets are isolated from other blood components, they are unstable and lose rapidly their functional properties.