Stratified squamous (nonkeratinized)

• Examine the various layers of cells and the superficial layers lining the uterine cervix. These are the cells that are sampled during “Pap tests” for cervical metaplasia.
• Observe the outer surface of the cornea to find stratified squamous (non-keratinized) epithelium.
• This is an example of nonkeratinized stratified squamous epithelium.
  • Note: Flattened cells in the superficial layers still have their nuclei.

What happens when an epithelium is subjected to chronic stress or injury?

• An epithelium usually maintains the structure characteristic of the organ in which it is found, but when subjected to prolonged irritation, it may become transformed to a different type better suited to resist the irritant. This is called epithelial metaplasia. This is a defense mechanism in which the transformed epithelium is sturdier and better able to withstand the chronic irritation.
  • Examples include the transformation of tracheal respiratory epithelium to stratified squamous in heavy smokers and esophageal stratified squamous epithelium to simple columnar (mucus-secreting) epithelium in persons with chronic gastro-esophageal reflux disorder.

Stratified keratinized squamous epithelium.