Epithelial tissue is one of the four basic types of animal tissue. Formed by juxtaposed cells, among which there is little extracellular substance. Since your cells have no blood vessels, nutrients are received through the underlying connective tissue.
The lining epithelial cells are joined with each other through structures called cell junctions. The various types of junctions serve not only as adhesion sites, but eventually also as seals preventing the flow of materials through the intercellular space, and they can also offer channels for communication between adjacent cells. Therefore, from a junctional point of view, junctions can be classified as adhesion junctions, tight junctions and communication junctions (gap junctions). In many epithelia several junctions are present in a constant sequence from the apex to the cell.
