A prostaglandin is any member of a group of lipid compounds that are derived from fatty acids and have important functions in the animal body. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring. They are mediators and have a variety of strong physiological effects; although they are technically hormones, they are rarely classified as such.
The prostaglandins together with the thromboxanes form the prostanoid class of fatty acid derivatives; the prostanoid class is a subclass of eicosanoids.
They are found in many vertebrate tissues where they act as messengers involved in reproduction and in the inflammatory response to infection. Aspirin inhibits prostaglandin synthesis, leading to reduced inflammation.