In this photograph, they are the small purple structures next to the lymphocyte. Platelets contain three distinct types of cytoplasmic granules, each containing different kinds of enzymes and chemical substances. Granule contents include Histamine Serotonin Platelet factor 4 Hydrolytic and proteolytic enzymes, and many others. As far as inflammation is concerned, platelets function primarily as secretory cells. Substances released from platelets mediate early blood vessel responses to inflammation and enhance vascular permeability.
Enzymes released from platelets can activate some of the complement components.
Additionally, platelets are a very important source of arachidonic acid metabolites.