A family of naturally occurring, biologically active substances derived from 20 carbon polyunsaturated fatty acids such as arachidonic acid. Members of the family include prostaglandins, thromboxanes, leukotrienes, and epoxyeicosatrienoic acids (EETs). Functioning as local hormones, they are synthesized and exert their biological actions in the same tissue. Many have physiological and pathological effects on the cardiovascular, pulmonary, reproductive, and digestive systems.