Microvesicles also originate from the endosomal membrane compartment after fusion of secretory granules with the plasma membrane, where they exist as intraluminal membrane-bound vesicles called exosomes. These exosomes are released from cells during exocytosis of secretory granules together with the proteins present inside these granules. MPs are released from the surface of membrane during membrane blebbing in a calcium flux and calpain-dependent manner and are relatively large (100 nm-1 μm). In contrast smaller exosomes that are more homogeneous in size (30-100 nm) are released from the endosomal compartment [42] . In the only paper reporting a direct comparison, the shedding vesicles of platelets 'could be detected by flow cytometry but not the exosomes, probably because of the smaller size of the latter' [43] .