2.6: Classification by shape of the cells at the free surface
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The three principal shapes associated with epithelial cells are—squamous, cuboidal and columnar.
- Squamous epithelium is composed of cells that are wider than their height (flat and wide).
- Cuboidal epithelium is composed of cells whose height and width are approximately the same (cube shaped).
- Columnar epithelium is composed of cells taller than they are wide.
By layer, epithelium is classed as either simple epithelium (one cell thick) or stratified epithelium (two or more cells thick), and both can be made up of any of the cell shapes. When epithelium is stratified, it is classified by the shape of the cells at the top or uppermost layer. A notable exception is pseudostratified epithelium. In this type of epithelium, taller simple columnar epithelial cells appear to have several nuclei at different heights, giving the appearance of stratification. However, in this type of epithelium, all the cells are attached to the basement membrane.
Urothelium (formerly called transitional epithelium) is another type of unique epithelium in which cells can change from squamous to cuboidal, depending on the amount of tension on the epithelium.
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