TRANSITIONAL EPITHELIUM – 1
The so-called transitional epithelium lines the bladder and other hollow areas of the urinary system. At first glance, it appears to be a stratified epithelium made up of several layers of spherical or polyhedral cells. However, it has two features that differentiate it from other stratified epithelia.
One is the presence of large cells in the most superficial layer of the epithelium. These cells have a dome-shaped free surface. You can see two of these cells cells of a group of three highlighted in blue (one the left and the cell on the right) when you place the cursor or click on the image. They are not, therefore, flat, squamous cells, like those found in stratified squamous epithelium.
One is the presence of large cells in the most superficial layer of the epithelium. These cells have a dome-shaped free surface. You can see two of these cells cells of a group of three highlighted in blue (one the left and the cell on the right) when you place the cursor or click on the image. They are not, therefore, flat, squamous cells, like those found in stratified squamous epithelium.
Bladder. Hematoxylin and eosin. Medium magnification.
The second feature that differentiate this type of epithelium from other stratified epithelia consists of the change of the epithelium thickness and of its cell shapes, depending on how full the bladder is.
When the bladder is empty or slightly full, the epithelial layer is thicker. When the bladder is full, the epithelium becomes thinner and the surface cells can become very flattened. The epithelial cells change their forms and adapt to the internal pressure in the bladder.
The text and drawings on the next page will help you to better understand this epithelium.