Prostaglandin biosynthetic pathway. Prostaglandins (PGs) are produced from cell membrane phospholipids from the precursor omega-6 polyunsaturated fatty acid, arachidonic acid. The cyclooxygenase enzymes are bifunctional enzymes that generate PGG2 and then the unstable intermediate PGH2. This intermediate is converted by tissue-specific synthases to PG that act on their respective receptors. cPGES, cytosolic prostaglandin E synthase; DP, prostaglandin E receptor; EP, prostaglandin E receptor; FP, prostaglandin F receptor; IP, prostaglandin I receptor; mPGES, microsomal prostaglandin E synthase; PGDS, prostaglandin D synthase; PGIS, prostaglandin I synthase; TP, thromboxane A receptor; TXS, thromboxane synthase; TXA2, thromboxane A2.