Epithelium

This article is about epithelium in animal anatomy. For the fungal structure of the same name, see Pileipellis.
Look up epithelium or squamous in Wiktionary, the free dictionary.

Epithelium
Types of epithelium
Identifiers
MeSHD004848
THH2.00.02.0.00002
FMA9639
Anatomical terms of microanatomy
This article is part of a series on
Epithelia
Squamous epithelial cell
Columnar epithelial cell
Cuboidal epithelial cell
Specialised epithelia
Other

Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial (mesothelial) tissues line the outer surfaces of many internal organs, the corresponding inner surfaces of body cavities, and the inner surfaces of blood vessels. Epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. These tissues also lack blood or lymph supply. The tissue is supplied by nerves.

There are three principal shapes of epithelial cell: squamous (scaly), columnar, and cuboidal. These can be arranged in a singular layer of cells as simple epithelium, either simple squamous, simple columnar, or simple cuboidal, or in layers of two or more cells deep as stratified (layered), 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 pseudostratified. All glands are made up of epithelial cells. Functions of epithelial cells include diffusion, filtration, secretion, selective absorption, germination, and transcellular transport. Compound epithelium has protective functions.

Epithelial layers contain no blood vessels (avascular), so they must receive nourishment via diffusion of substances from the underlying connective tissue, through the basement membrane.[1][2]: 3  Cell junctions are especially abundant in epithelial tissues.

  1. ^ Eurell JA, Frappier BL, eds. (2006). Dellmann's Textbook of Veterinary Histology. Wiley-Blackwell. p. 18. ISBN 978-0-7817-4148-4.
  2. ^ Freshney RI (2002). "Introduction". In Freshney RI, Freshney M (eds.). Culture of epithelial cells. John Wiley & Sons. ISBN 978-0-471-40121-6.