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The stratified squamous epithelium consists of cell layers in which the superficial layer consists of squamous epithelial cells while the underlying cell layers have various types of cells. The deepest layer is made up of columnar cells. This type of epithelial tissue covers body parts that are exposed to frequent frictional forces or stress.
Stratified Squamous Epithelium Structure
The structure of this type of epithelium is made up of several layers of cells with the columnar cells of the basal layer resting on the basement membrane. Lying over these columnar cells as we pass towards the surface of the epithelium are cells that become progressively flat so that the most superficial cells consist of flattened squamous cells giving it the name stratified squamous epithelium.
Types of stratified squamous epithelia
There are two main types of stratified squamous epithelium which are the non-keratinized and keratinized. When the surface of the epithelium remains moist with the most superficial squamous cells having nuclei and are living cells, then such type is referred to as non-keratinized stratified squamous epithelium but when the most superficial squamous cells are dead and without any nuclei, the tissue is called keratinized stratified squamous epithelial tissue (and the dead cells of the keratinized type contain a substance called keratin that forms a non-living covering over the epithelium). As a result of frequent frictional forces, the most superficial layers are constantly being removed and are replaced by proliferation of cells from the basal (or germinal) layer of the stratified squamous epithelium which makes – the superficial layer therefore, shows frequent mitoses.
Stratified Squamous Epithelium Function
The function of stratified squamous epithelium is to protect the tissues and organs they cover as they are continually exposed to stress and friction. The ability of the stratified squamous epithelium to regenerate quickly helps it to best serve this function.
Where is Stratified Squamous Epithelium Found?
Stratified squamous epithelium is found in surfaces of the body that undergo constant wearing forces or parts of the body having frequent friction such as the mouth, skin, and cornea.
Stratified Squamous Epithelium Location
- The epidermis of the skin is made up of keratinized stratified squamous epithelium but the dermis is made of connective tissue. Even though the epidermis is referred to as a type of stratified squamous epithelial tissue, the majority of cells in it are not squamous (flattened) cells.
- The vocal folds of the larynx are covered by stratified squamous epithelium even though it does not come in contact with swallowed food but because it is exposed to stress during speech as it vibrates.
- The oral cavity mucosa (lining of the oral cavity) is made up of stratified squamous epithelium; as the mouth is used for eating and speech, it is exposed to frictional forces
- Cornea of the eyes because of the constant blinking of the eyelids and movement of the eyeballs, the cornea is exposed to frictional forces and therefore is made up of non-keratinized stratified squamous epithelium to protect it from these wearing forces.
- The surface of the tongue
- The mucosa of the esophagus is lined by non-keratinized stratified squamous epithelium
- Palatine tonsils are lined by stratified squamous epithelium
- The distal part of the urethra towards the urethral meatus is lined by stratified squamous epithelium
- The external acoustic meatus of the ears is covered by stratified squamous epithelium that extends from the auricle to the middle ear