Q. What are the differentiations of the cell membrane?

In some kind of cells, the cell membrane presents differentiations that are necessary for the specific functions of the cells. The major differentiations are the microvilli and the structures for strengthening of adhesion or union between 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 beneficial to increase 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 strengthening of adhesion between cells occur mainly in epithelial tissues where the need for coverage and impermeability requires cells to be "glued" to neighboring cells. These differentiations can be desmosomes, interdigitations, tight junctions (zonula occludens), zonula adherens (adherens junctions) and gap junctions.