**3. Alpha granules**

It is widely accepted that these granules come from the budding of trans golgi apparatus organel of megakaryocytes (16, 17).

These are 200-400 nm diameter granules widespread in the cytoplasm (16) which gives the granular appearance in Romanoski stained smear preparations, each platelet contains around 50-80 of these granules. The content of granules is very diverse; a brief list is given in table 1 (14, 18, 19, 20, 21).

When platelets are activated these alpha granules fuse with each other, OCS and plasma membrane. The secretion of alpha granules is mediated by some proteins (such as SNARE) and membrane lipids (19).

The secretions effect platelet and cells in the environment (such as endothelial, leukocytes) for migration, adhesion and proliferation(14).

A rare syndrome named as Gray Thrombocyte Syndrome (GTS) is both involved with the quantity and quality of platelets which cases susceptibility for bleeding. In GTS the proteins synthesized by megakaryocytes are abnormal and don't enter platelets as they do in normal individuals and additionally the endocytotic mechanisms don't work properly. As a result the secretions spread to bone marrow and a fibrosis forms (miyelofibrozis)(22, 23).


**Table 1.** Some main components of alpha granules.
