Explain the intercellular junctions found on the lateral sur

Explain the intercellular junctions found on the lateral surface of an epithelial cell starting from the apical pole and progressing to the basal pole of the cell. How is the terminal bar seen on a light microscope related?

Solution

Epithelia are tissues composed of closely aggregated cells that cover most body surfaces, cavities, and tubes. Surface epithelia form continuous sheets that can have one or multiple cell layers. Several different types of cell junctions mediate physical strength and cell communication within the epithelium. A basement membrane lies beneath the epithelium and separates it from underlying tissue; because blood vessels do not penetrate the basement membrane, nutrients like oxygen and metabolites reach the epithelium by diffusion. Epithelia are polarized, with an apical surface that faces the external environment and a basal surface that faces the basement membrane. Microvilli are small processes that project from the apical surface of most types of epithelial cells, greatly increasing the surface area. They are notably found at the intestinal brush border and in the proximal convoluted tubule of the kidney. Stereocilia are unusually long, non-motile microvilli that are found on the surface epithelium in the epididymis and ductus deferens. Cilia are actively motile processes with a complex internal structure found on the epithelial lining of the respiratory tract and the female reproductive tract. The basement membrane, a thin non-cellular layer, intervenes between the epithelium and the connective tissue. This membrane is 30 to 60 nanometers thick and made up of collagenous and non-collagenous glycoproteins and proteoglycans. It provides structural support for the epithelium and serves as a selective barrier for the movement of materials to and from the supporting tissue. Using light microscopy, terminar bar appears as a bar at the apical surface of the cell, wherein the structures listed cannot be resolved. With electron microscopy, the terminal bar can be visually disseminated into these structures. The terminal bar is located on the lateral surface of epithelial cells, where the lateral surface meets the apical surface. It should not be confused with the Terminal web, which is an actinous web underlying microvilli on specialized epithelial cells