Platelets

Stem cells differentiate into cells that produce platelets.

Myeloid stem cells in the presence of thrombopoietin hormone develop into megakaryocyte colony forming cells that develop into megakaryoblasts. 

Megakaryoblasts convert into megakaryocytes which many cells splinter into 2000 to 3000 fragments. Each fragments link by a small portion of the plasma membrane that is a platelet, also known as thrombocyte . 

Platelets Flow Chart

Platelets break off from megakaryocytes in red bone marrow and then enter in bloodstream. 

• Normal value of platelets is 150,000-400,000 in each microliter of blood. 
• Platelets size: 2-4µm in diameter
• Platelets shape: irregularly disc shaped
• Platelets contain many vessels but no nucleus.  
• Platelets span short life, normally 5-9days.
• Dead platelets are removed by macrophages in spleen and liver.

Functions of platelets

1. Platelets promote blood clotting.
2. It also promotes vascular spasm.