What are differentiations of the cell membrane?

In some types of cells, the cell membrane presents differentiations that are essential for the specific functions of the cells. The major differentiations are the microvilli and the structures for reinforcement of adhesion or union among cells (cell junctions).

Microvilli are multiple external projections of the membrane resembling glove fingers. This differentiation is found in cells of tissues where it is advantageous to enhance the size of the surface area in contact with the exterior, for instance, in the enteric (intestinal) epithelium for absorption of nutrients.

Membrane differentiations for reinforcement of adhesion among cells occur mainly in epithelial tissues where they require for coverage and impermeability needs cells to be "glued" to neighboring cells. These differentiations can be interdigitations, desmosomes, tight junctions (zonula occludens), zonula adherens (adherens junctions) and gap junctions.