MAIN FEATURES OF THE EPITHELIAL CELLS
The epithelial cells maintain A narrow space with their neighbours. They are juxtaposed and there is very little extracellular material between them. The cells establish many intercellular junctions with each other.
The shape of its cells is quite diverse, from flat to pyramidal, including, cuboidal and columnar shapes. Recall cell shapes in Chapter 1.
With very few exceptions, the epithelial tissue does not contain blood vessels.
The epithelial cells are always supported by a connective tissue that contains blood and lymphatic vessels and supply oxygen, nutrients and other molecules to the epithelial cells.
In most of the interfaces between epithelial cells and the connective tissue exist a complex and very thin layer of macromolecules called the basal lamina that support the epithelial cells.
The basal lamina of most epithelia is very thin and can not be observed with an optical microscope. Nevertheless, many epithelia seen with an optical microscope, especially in sections treated by some procedures such as the PAS (Periodic Acid-Schiff technique) seem to be sustained by a membrane.This membrane is called which is called the basal membrane.The basal membrane is an associationof components of its underlying connective tissuebetween the basal epithelial cell membrane and is the. This may be seen very
layer that is are together with components of its underlying connective tissue When observed ,is often seen as a thicker layer called the basal membrane.
The basal lamina together with components of its underlying connective tissue When observed with an optical microscope,is often seen as a thicker layer called the basal membrane.
Most epithelial cells have specific organization of their orgnelles called polarization. Polarization means that different regions of cells have characteristic organizations and different organelle contents resulting in different functions of these different regions of the cells.
As a result of their polarization, the portion of the cell that rests on the basal lamina is called the basal region and the opposite portion, often facing a cavity or an open space, is called the apical region.
Epithelial cells very often have in their membranes facing an open space such as the lumen of an organ microvilli, cilia, stereocilia, in addition to intercellular junctions.