Platelets are derived from a quiescent stem cell. In this bone marrow milieu, bathed in various cytokines and growth factors, such as IL-6 and G-CSF and GM, they gradually differentiate from an activated stem cell, on to committed stem cells that are en route to megakaryocytes.

Platelets are derived from Megakaryocytes.

• Released from megakaryocytes by fragmentation of the megakaryocyte cytoplasm
• NO DNA
• NO Nucleus
• Proteins:  structural, granule (stored), glycoproteins, enzyme

• Electron dense granules:  adenine nucleotides, Ca2+, 5HT
• specific alpha granules:  GF, fibrinogen, Factor V, vWF, fibronectin, B-thromboglobulin, PF4, thrombospondin
• Lysosomes:  acid hydrolases
• Plasma membrane:  PF-3 (receptors for clotting factors and aggregating factors)