<P> In human physiology there are two main types of epithelia using distinct types of barrier mechanism . Epidermal structures such as skin form a barrier from many layers of keratinized squamous cells . Internal epithelia on the other hand more often rely on tight junctions for their barrier function . This kind of barrier is mostly formed by only one or two layers of cells . It was long unclear whether tight cell junctions also play any role in the barrier function of the skin and similar external epithelia but recent research suggests that this is indeed the case . </P>
where can tight junctions be found in the body
Internal epithelia