Question

1. Most epithelia are considered simple or stratified. What is the basis for calling an epithelium pseudostratified as opposed to either simple of stratified?

2. What structure feature accounts for an epithelium to be stratified even when it is not really stratified?

3. Epithelia are characterized by the presence of a variety of junctions between neighboring cells. An epithelium that makes up the wall of a duct, what type of junctions MUST be present? Explain why

Answer 1

1) Simple epithelia is made up of a single layer of cells and stratitified epithilia are composed of two or more layer of cells. Pseudostratified epithelia in actual is simple epithelia which is made of only a single layer of cells but, when observing the section of this epithilia it appears to be like straified epithilia which is made of multiple layer of cells. That is it gives a false impression just by appearing like a stratified tissue. Hence, this particular epithelium is named as ' pseudostratified ' as opposed to either simple or stratified.

2) The structural feature that accounts for an epithelium to be stratified even when it is not really stratified is the location of nucleus present. Here, the nucleus of pseudostratified epithelia is not present in the same level . so, while observing the sections of these epithelia it gives a false information that the epithelia is stratified.

3) In epithelium that makes up the walls of ducts usually gap junctions must be present. It is because, they provide channels for the movement of ions, sugar, proteins etc. But, tight junctions are impermeable or they act as barrier for the movement of molecules. On the otherhand, adherens junctions are present where there is a chance for stress.