Platelet electron microscopy demonstrates absence of alpha granules
29) This partially active FV is then stored in platelet alpha granules
, where it appears that this partial activation also renders platelet FV resistant to circulating inhibitors.
BT and PF4 are platelet-specific chemokines and are stored in the platelet alpha granules
and released into the blood once the platelets are activated.
Since factor V, vWF and fibrinogen are also included in alpha granules
, some aggregation defect is also observed in specific deficiencies of these.
For example, PLT alpha granules
, whose contents are released into the vascular space following PLT activation, are rich in many important mediators of hemostatic and nonhemostatic processes, such as procoagulants factor V and von Willebrand factor, mitogens like PLT-derived growth factor, other cytokines such as RANTES (chemokine ligand 5; regulated on activation, normal T cell expressed and secreted), immunoglobulins, and antimicrobial proteins.