Arachidonic Acid is a C20 carboxylic acid with 4 isolated double bonds at positions 5, 8, 11 and 14. This esterified fatty acid is released from phospholipids in cell membranes by the action of phospholipase A2, activated by pro-inflammatory cytokines. Further enzymatic processing of arachadonic acid results in the production of a range of prostanoids (prostaglandins and thromboxanes). This includes PGE2 (this has a role in limiting inflammation by inhibiting production of some cytokines such as interleukin–1), and TXA2 (involved in platelet aggregation and haemostasis). Metabolites are named “eicosanoids” referring to the common structural feature of 20 carbon atoms.