Eicosanoids are biological signalling molecules.
they act as short range messengers affecting tissues near 
the cells that produce them.

all 3 sub classes of eicosanoids are 
prostaglandins,thromboxanes,leukotrienes,which are unstable 
and insoluble in water.
these act primarily on cells very near their point of 
release.

phospholipase present in mammalian cells  attack the 
membrane phospholipids and releases arachidonate.
arachidonate is is conerted into PGH2 precursor of 
prostaglandins and thromboxanes.

eicosanoids are polyunsaturated fatty acid type of lipid 

and yes there 4 subclasses of eicosanoids
1. prostaglandins
2.thromboxane
3.leukotriene
4.prostacyclins