The cell membrane consists primarily of a thin layer of amphipathic phospholipids which spontaneously arrange so that the hydrophobic `` tail '' regions are shielded from the surrounding polar fluid , causing the more hydrophilic `` head '' regions to associate with the cytosolic and extracellular faces of the resulting bilayer .

Structure The membrane is made up of a thin layer called the `` phospholipid bilayer '' .
