In platelets, the term "alpha granules" is used to describe granule

Granule (cell biology)

In cell biology, a granule is a small particle. It can be any structure barely visible by light microscopy. The term is most often used to describe a secretory vesicle.-Leukocytes:...

s containing several growth factors.

Contents

Contents include insulin-like growth factor 1

Insulin-like growth factor 1

Insulin-like growth factor 1 also known as somatomedin C is a protein that in humans is encoded by the IGF1 gene. IGF-1 has also been referred to as a "sulfation factor" and its effects were termed "nonsuppressible insulin-like activity" in the 1970s.IGF-1 is a hormone similar in molecular...

, platelet-derived growth factor

Platelet-derived growth factor

In molecular biology, platelet-derived growth factor is one of the numerous growth factors, or proteins that regulate cell growth and division. In particular, it plays a significant role in blood vessel formation , the growth of blood vessels from already-existing blood vessel tissue. Uncontrolled...

, TGFβ, platelet factor 4

Platelet factor 4

Platelet factor 4 is a small cytokine belonging to the CXC chemokine family that is also known as chemokine ligand 4 . This chemokine is released from alpha-granules of activated platelets during platelet aggregation, and promotes blood coagulation by moderating the effects of heparin-like...

 (which is a heparin-binding chemokine) and other clotting proteins (such as thrombospondin

Thrombospondin

Thrombospondins are secreted proteins with antiangiogenic abilities. TSP was discovered by Nancy L. Baenziger.-Types:The thrombospondins are a family of multifunctional proteins...

, fibronectin

Fibronectin

Fibronectin is a high-molecular weight glycoprotein of the extracellular matrix that binds to membrane-spanning receptor proteins called integrins. In addition to integrins, fibronectin also binds extracellular matrix components such as collagen, fibrin and heparan sulfate proteoglycans...

, and von Willebrand factor.

The alpha granules express the adhesion molecule P-selectin

P-selectin

P-selectin is a cell adhesion molecule on the surfaces of activated endothelial cells, which line the inner surface of blood vessels, and activated platelets...

 and CD63

CD63

CD63 antigen is a protein that in humans is encoded by the CD63 gene.CD63 is a good marker for flow cytometric quantification of in vitro activated basophils for diagnosis of IgE-mediated allergy. The test is commonly designated as basophil activation test -Interactions:CD63 has been shown to...

. These are transferred to the membrane after synthesis.

The other type of granules within platelets are called dense granules.