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A stratified squamous epithelium consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity. Although this epithelium is referred to as squamous, many cells within the layers may not be flattened; this is due to the convention of naming epithelia according to the cell type at the surface. In the deeper layers, the cells may be columnar or cuboidal. There are no intercellular spaces. This type of epithelium is well suited to areas in the body subject to constant abrasion, as the thickest layers can be sequentially sloughed off and replaced before the basement membrane is exposed. It forms the outermost layer of the skin and the inner lining of the mouth,
esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to t ...
and vagina. In the epidermis of skin in mammals, reptiles, and birds, the layer of
keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up Scale (anatomy), scales, hair, Nail ...
in the outer layer of the stratified squamous epithelial surface is named the stratum corneum. Stratum corneum is made up of squamous cells which are keratinized and dead. These are shed periodically.


Structure


Non-keratinized

Non-keratinized surfaces must be kept moist by bodily secretions to prevent them from drying out. Cells of stratum corneum are sometimes without keratin and living. Examples of non-keratinized stratified squamous epithelium include some parts of the lining of oral cavity,
pharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its st ...
,
conjunctiva The conjunctiva is a thin mucous membrane that lines the inside of the eyelids and covers the sclera (the white of the eye). It is composed of non-keratinized, stratified squamous epithelium with goblet cells, stratified columnar epithel ...
of eye, upper one-third
esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to t ...
, rectum, external female genitalia, and vagina. Even non-keratinized surfaces, consisting as they do of keratinocytes, have a minor superficial keratinized layer of varying thickness, depending on the age of the epithelium and the damage it has experienced.


Keratinized

Keratinized surfaces "s are protected from absorption by
keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up Scale (anatomy), scales, hair, Nail ...
protein. Keratinized epithelium has keratin deposited on the surface which makes it impermeable and dry. Examples of keratinized stratified squamous epithelium include skin, the epidermis of the palm of the hand, and the sole of the foot, and the masticatory mucosa.


Gallery

File:Illu epithelium.jpg, Epithelium File:Barretts_alcian_blue.jpg, icrographof normal stratified squamous epithelium and the metaplasic epithelium of
Barrett's esophagus Barrett's esophagus is a condition in which there is an abnormal ( metaplastic) change in the mucosal cells lining the lower portion of the esophagus, from stratified squamous epithelium to simple columnar epithelium with interspersed goblet cells ...
(left of image). Alcian blue stain. File:Stratified suqamous epithelium animated.gif, Non-keratinized stratified squamous epithelium, image highlights the epithelial nucleuses, rest of the epithelial layer, underlying connective tissue and other epithelia


References

{{Authority control Epithelium