Stratified squamous (nonkeratinized) (Fig. 4-14)

• Scan the epithelium lining the larynx (slide 7) and cornea (slide 78), observing the change to stratified squamous epithelium in the larynx.
• This is an example of nonkeratinized stratified squamous epithelium.
  • Note: Flattened cells in the superficial layers still have their nuclei.

What functional similarities and what differences are indicated by the two types of epithelia lining the larynx and trachea?

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.