A stratified squamous epithelium consists of squamous (flattened)
epithelial cell
Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...
s 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
In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...
,
esophagus and
vagina.
In the
epidermis
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...
of
skin in
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s,
reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s, and
birds, the layer of
keratin in the outer layer of the stratified squamous epithelial surface is named the
stratum corneum
The stratum corneum (Latin for 'horny layer') is the outermost layer of the epidermis. The human stratum corneum comprises several levels of flattened corneocytes that are divided into two layers: the ''stratum disjunctum'' and ''stratum compact ...
. 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
The stratum corneum (Latin for 'horny layer') is the outermost layer of the epidermis. The human stratum corneum comprises several levels of flattened corneocytes that are divided into two layers: the ''stratum disjunctum'' and ''stratum compact ...
are sometimes without keratin and living.
Examples of non-keratinized stratified squamous epithelium include some parts of the lining of
oral cavity,
pharynx,
conjunctiva of
eye
Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...
, upper one-third
esophagus,
rectum
The rectum is the final straight portion of the large intestine in humans and some other mammals, and the Gastrointestinal tract, gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the s ...
,
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 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 (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
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Epithelium