These are phospholipids containing choline. They are the most abundant phospholipids of the cell membrane and represent a large proportion of the body’s store of choline.  Most phospholipids have a saturated acyl radical in the sn-1 position but an un-saturated radical in the sn -2 position of glycerol. Choline is important in nervous transmission, as acetylcholine, and as a store of labile methyl groups. Dipalmitoyl lecithin is a very effective surface-active agent and a major constituent of the surfactant preventing adherence due to surface tension, of the inner surfaces of the lungs. They lower surface tension of water molecule and helps in the emulsification of fat.