page_title: Epithelium
section_title: Clinical significance
hierarchical_section_title: Epithelium / Clinical significance
caption_attribution_description: English: Chlamydia pneumoniae in epithelial cell. Acute bronchitis. 1 - infected epitheliocyte, 2 - uninfected epitheliocytes, 3 - chlamydial inclusion bodies in cell, 4 - cell nuclei. Micrograph Русский: Chlamydia pneumoniae в клетке плоского эпителия при остром бронхите. 1 - инфицированная клетка, 2 - неинфицированные клетки, 3 - тельца включения C.pneumoniae в инфицированной клетке, 4 - ядра клеток. Микрофотография орашенного мазка. Объектив 100x (масляная иммерсия). Способ окраски - согласно пат. РФ № 2281472
context_page_description: Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs. An example is the epidermis, the outermost layer of the skin.
  There are three principal shapes of epithelial cell: squamous, columnar, and cuboidal. These can be arranged in a single layer of cells as simple epithelium, either squamous, columnar, or cuboidal, or in layers of two or more cells deep as stratified, or compound, either squamous, columnar or cuboidal. In some tissues, a layer of columnar cells may appear to be stratified due to the placement of the nuclei. This sort of tissue is called a pseudostratified. All glands are made up of epithelial cells. Functions of epithelial cells include secretion, selective absorption, protection, transcellular transport, and sensing.
  Epithelial layers contain no blood vessels, so they must receive nourishment via diffusion of substances from the underlying connective tissue, through the basement membrane.
context_section_description: The slide shows at (1) an epithelial cell infected by Chlamydia pneumoniae; their inclusion bodies shown at (3); an uninfected cell shown at (2) and (4) showing the difference between an infected cell nucleus and an uninfected cell nucleus.
  Epithelium grown in culture can be identified by examining its morphological characteristics. Epithelial cells tend to cluster together, and have a "characteristic tight pavement-like appearance". But this is not always the case, such as when the cells are derived from a tumor. In these cases, it is often necessary to use certain biochemical markers to make a positive identification. The intermediate filament proteins in the cytokeratin group are almost exclusively found in epithelial cells, so they are often used for this purpose.
  Cancers originating from the epithelium are classified as carcinomas. In contrast, sarcomas develop in connective tissue.
  When epithelial cells or tissues are damaged from cystic fibrosis, sweat glands are also damaged, causing a frosty coating of the skin.
caption: Epithelial cell infected with Chlamydia pneumoniae
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