The body produces many hormones which allow the body to operate in a variety of ways. One group of these hormones are called local hormones, or eicosanoids. What are eicosanoids? The eicosanoids definition is a hormone that is derived from arachidonic acid and only acts on cells nearby to where it was produced, instead of being transported to another location in the body. A hormone that only reacts in the area it was produced is called a paracrine hormone, but it is also known as a local hormone. Eicosanoids that are produced in the knee, only send signals to cells in the immediate knee area to act. For example, if the knee is injured the body produces eicosanoids in the knee region that signal that area to induce swelling. But the eicosanoids do not signal any other areas of the body to start swelling.Eicosanoids are formed from arachidonic acid. Arachidonic acid is an omega-6 polyunsaturated fatty acid, with 20 carbons atoms in the chain. Arachidonic acids in the necessary region will be converted into the needed eicosanoid. This may require the formation of a 5 or 6 membered ring using carbon atoms 8 through 12, or moving and adding the carbon-carbon double bonds. Prostaglandins form a 5 membered ring from the carbon atoms 8 through 12 on the arachidonic acid Leukotrienes form 3 conjugated double bonds on the arachidonic acid Thromboxanes form a 6 membered ring using carbon atoms 8 through 12 on the arachidonic acid plus an oxygen