Short notes on the structure of stratified epithelium
Stratified squamous epithelium:
The tissue consists of several layers of cells. The numbers of layers in the tissue are varied in different parts of the body. The basal layer rests on a basement membrane and continuously divides mitotically to produce a number of new cells.
There is a gradual change in the shape and form of the cells as they approach the superficial layers. The upper layers are composed of flat, plate like cells. The cells of the superficial layers are constantly removed and replaced by the fresh layers of cells produced from beneath. The cells of the surface layers are very thin and have flat nuclei.
The stratified squamous epithelium may be classified into two categories-
Keratinized and Non Keratinized:
Keratinized stratified squamous epithelium: The cells of the outer layers have their cytoplasm replaced with a hard waterproof protein called keratin. The process of replacement of cytoplasm is called keratinisation or karnification. The keratinised cells are dead cells and are referred to as horny layers eg. the epidermis of the skin in land vertebrates or terrestrial vertebrates.
Non Keratinized Stratified Squamous epithelium:
This tissue lines the buccal cavity, pharynx and oesophagus. Here the cells are living even at the surface because cytoplasm is not replaced by keratin. This layer however is not waterproof and affords some degree of protection.