Eicosatetraenoic acid

Eicosatetraenoic acid designates any straight chain 20:4 fatty acid.
 * See essential fatty acid for nomenclature.

Two isomers, both of them essential fatty acids, are of particular interest:
 * all-cis 5,8,11,14-eicosatetraenoic acid is an ω-6 fatty acid with the trivial name arachidonic acid. It is formed by a desaturation of dihomo-gamma-linolenic acid 20:4 ω-6.
 * all-cis 8,11,14,17-eicosatetraenoic acid is an ω-3 fatty acid. It is an intermediary between stearidonic acid (18:4 ω-3) and eicosapentaenoic acid (EPA, 20:5 ω-3)

Some chemistry sources define 'arachadonic acid' to designate any of the eicosatetraenoic acids. However, almost all writings in biology, medicine and nutrition limit the use the term 'arachidonic acid' to all-cis 5,8,11,14-eicosatetraenoic acid (ω-6).