The<unk>  of a polarized cell is the part of the plasma<unk>  that forms its lumenal surface, distinct from the basolateral<unk> . This is particularly evident in epithelial cells, but also describes other polarized cells, such as neurons.
Tight junctions that join epithelial cells near their<unk>  surface prevent the migration of proteins to the<unk> . The basal and lateral surfaces thus remain roughly equivalent to one another, yet distinct from the<unk>  surface.
Referring to the tip (apex) of a cell, an organ or other body structure. For example, epithelial cells have their<unk>  surface exposed to the body exterior, or (depending on their location) an internal open space like the intestinal lumen.
Apical membrane
Basolateral membrane
Tight junction
Adherens junction
Gap junction
Hemidesmosome
Nuclear envelope
Golgi apparatus