Final answer:
Nonkeratinized stratified squamous epithelium is kept moist by mucus or bodily fluids like saliva. It protects underlying tissues in the mouth, esophagus, vagina, and rectum from abrasion, differing from keratinized epithelium in its need for moisture due to lack of keratin.
Step-by-step explanation:
Nonkeratinized stratified squamous epithelium is a type of tissue that consists of multiple layers of cells, with the most apical layer being flat, scale-like cells. This tissue type is kept moist by secretions such as mucus or body fluids like saliva, which serves to protect the underlying tissues from abrasion and friction. Due to the lack of keratin, a protective protein found in keratinized tissues, nonkeratinized tissues require this moisture to stay healthy and to fulfill their protective function.
In the human body, you can find nonkeratinized stratified squamous epithelium lining the inside of the mouth, the esophagus, the vagina, and part of the rectum. Unlike keratinized stratified squamous epithelium, which forms the outer layer of the skin and contains dead cells filled with keratin, nonkeratinized epithelium does not have this layer of keratin and thus needs to be kept moist to prevent drying out and to maintain its protective properties.