b) Stratified Epithelium : composed of two or more layers of cells. Because of this it is more durable and better able to protect underlying tissues. 1) Stratified Squamous Epithelium: Cells in the apical layer are flat, while those of the deep layers vary in shape from cuboidal to columnar. The basal (deepest) cells continuously undergo cell division and pushed upward to the apical layer. Older cells at the apical layer die and are sloughed off making way for the newer cells. They can exist as keratinized and nonkeratinized forms.
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2) Stratified Cuboidal Epithelium: A rare type of epithelium inwhich cells of the apical layer are cuboidal. This typemainly serves as a protective function.
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3) Stratified Columnar Epithelium: Also, a rare type of epithelium. The basal layers have shortened irregular cells while the apical layer has cells that are columnar in shape. This type also functions mainly as a protection layer and some secretion.
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4) Transitional Epithelium: Has a variable appearance. In its relaxed unstretched state is appears like stratified cuboidal epithelium except the cells in the apical layer appear large and round. If the tissue is stretched, the cells become flatter giving a more stratified squamous epithelium appearance. This type of epithelium is only found in the urinary system allowing for a greater degree of stretch without rupture.
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c) Pseudostratified Epithelium Known as pseudostratified columnar epithelium and appears to have several layers because the nuclei of the cells are at various depths. When viewed from the side, this gives a false impression of multiple layers. Thus, the name pseudo (false). The cells that extend to the apical surface either secrete mucus or have cilia. The mucus traps foreign particles and the cilia sweep away mucus for elimination from the body.
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