Skin is keratinized. The outermost layer, the stratum corneum, is composed of keratinized squamous cells. These cells are dead and filled with keratin, a tough protein that provides protection. This keratinization is a key characteristic of the skin of reptiles, birds, and mammals, forming a protective barrier against the environment.
Understanding Keratinization
Keratinization is the process by which cells produce and accumulate keratin. This process results in the formation of tough, protective layers of dead cells. The skin's keratinized layer continuously sheds and is replaced, maintaining its integrity and function. Conversely, non-keratinized stratified squamous epithelium, found in areas like the lining of the mouth and esophagus, lacks this protective layer of keratin and needs to be kept moist by body fluids.
Examples of Keratinized and Non-Keratinized Epithelium
- Keratinized: Skin (epidermis), the outer layer of the gingiva (gums) and hard palate.
- Non-keratinized: Lining of the mouth (buccal cavity), esophagus, and conjunctiva of the eyelids.
The presence or absence of keratin is a defining characteristic differentiating these types of epithelium. The references highlight this difference, pointing out that keratinized stratified squamous epithelium is found in the skin, while non-keratinized epithelium is found in moist areas like the buccal cavity. The stratum corneum, explicitly described as composed of keratinized squamous cells, further reinforces the keratinized nature of the skin. The continual shedding of dead, keratinized cells is a crucial aspect of the skin's protective function.
