Prostaglandins are

Unsaturated Fatty Acids Contain One or More Double Bonds Unsaturated fatty acids may be further subdivided as follows: Monounsaturated (monoethenoid, monoenoic) acids, containing one double bond. Polyunsaturated  (polyethenoid,  polyenoic)  acids,  containing two or more double bonds. Eicosanoids: These compounds, derived from eicosa (20-carbon) polyenoic fatty acids, comprise the prostanoids, leukotrienes (LTs), and lipoxins (LXs).  Prostanoids include prostaglandins (PGs), prostacyclins (PGIs), and thromboxanes (TXs). HARPERS ILLUSTRATED BIOCHEMISTRY30th ed, Page No:213