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A stratified squamous epithelium consists of squamous (flattened)
epithelial cell Epithelium () is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume ...
s arranged in layers upon a
basal membrane cell membrane vs. Prokaryotes The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates the interior of all cells from the out ...
. 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 Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have differe ...

skin
and the inner lining of the
mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...

mouth
,
esophagus The esophagus (American English) or oesophagus (British English; American and British English spelling differences#ae and oe, see spelling differences) (), informally known as the food pipe or gullet, is an Organ (anatomy), organ in vertebrate ...

esophagus
and
vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the Vulval vestibule, vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucous membrane, ...

vagina
. In the
epidermis The epidermis is the outermost of the three layers that make up the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the am ...

epidermis
of
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have differe ...

skin
in
mammals Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the R ...
,
reptiles Reptiles are tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids ...

reptiles
, and
birds Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...
, 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 ...

keratin
in the outer layer of the stratified squamous epithelial surface is named the
stratum corneum The ''stratum corneum'' (Latin language, Latin for 'horny layer') is the outermost layer of the epidermis (skin), epidermis. There has been a long-standing belief in dermatology that the stratum corneum consisted of dead cell (biology), cells (co ...
. 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 language, Latin for 'horny layer') is the outermost layer of the epidermis (skin), epidermis. There has been a long-standing belief in dermatology that the stratum corneum consisted of dead cell (biology), cells (co ...
are sometimes without keratin and living. Examples of non-keratinized stratified squamous epithelium include some parts of the lining of
oral cavity In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...
,
pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx
,
conjunctiva The conjunctiva is a tissue that lines the inside of the eyelid An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving visio ...
of
eye Eyes are organs of the visual system The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which ...

eye
, upper one-third
esophagus The esophagus (American English) or oesophagus (British English; American and British English spelling differences#ae and oe, see spelling differences) (), informally known as the food pipe or gullet, is an Organ (anatomy), organ in vertebrate ...

esophagus
,
rectum The rectum is the final straight portion of the large intestine in humans and some other mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and ...

rectum
,
external female genitalia
external female genitalia
, and
vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the Vulval vestibule, vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucous membrane, ...

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 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 ...

keratin
protein. Keratinized epithelium has keratin deposited on the surface which makes it impermeable and dry. Examples of keratinized stratified squamous epithelium include skin, epidermis of the palm of the hand and sole of the foot, and the
masticatory mucosa
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 normal stratified squamous epithelium to simple columnar epithelium with interspersed goblet ...
(left of image).
Alcian blue stain Alcian blue () is any member of a family of polyvalent basic dyes, of which the Alcian blue 8G (also called Ingrain blue 1, and C.I. 74240, formerly called Alcian blue 8GX from the name of a batch of an Imperial Chemical Industries, ICI product) ...
. 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