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 [ep″ĭ-the´le-um] (pl. epithe´lia) (Gr.)
the cellular covering of internal and external surfaces of the body, including the lining of vessels and other small cavities. It consists of cells joined by small amounts of cementing substances. Epithelium is classified into types on the basis of the number of layers deep and the shape of the superficial cells.
ciliated epithelium epithelium bearing vibratile, hairlike processes (cilia) on its free surface.
columnar epithelium epithelium whose cells are of much greater height than width.
cuboidal epithelium epithelium whose cells are of approximately the same height and width, and appear square in transverse section.
germinal epithelium thickened peritoneal epithelium covering the gonad from earliest development; formerly thought to give rise to germ cells.
glandular epithelium that composed of secreting cells.
pigmentary epithelium (pigmented epithelium) that made of cells containing granules of pigment.
sense epithelium (sensory epithelium) neuroepithelium (def. 1).
simple epithelium that composed of a single layer of cells.
squamous epithelium that composed of flattened platelike cells.
stratified epithelium epithelium made up of cells arranged in layers.
transitional epithelium a type characteristically found lining hollow organs, such as the urinary bladder, that are subject to great mechanical change due to contraction and distention; originally thought to represent a transition between stratified squamous and columnar epithelium.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


, pl.


(ep'i-thē'lē-ŭm, -ă), [TA]
The purely cellular avascular layer covering all free surfaces, cutaneous, mucous, and serous, including the glands and other structures derived therefrom.
[G. epi, upon, + thēlē, nipple, a term applied originally to the thin skin covering the nipples and the papillary layer of the border of the lips]
Farlex Partner Medical Dictionary © Farlex 2012


n. pl. epithe·lia (-lē-ə) or epithe·liums
Membranous tissue composed of one or more layers of cells separated by very little intercellular substance and forming the covering of most internal and external surfaces of the body and its organs.

ep′i·the′li·al adj.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


, pl. epithelia (ep'i-thē'lē-ŭm, -ă) [TA]
The purely cellular avascular layer covering all the free surfaces, cutaneous, mucous, and serous, including the glands and other structures derived therefrom.
[G. epi, upon, + thēlē, nipple, a term applied originally to the thin skin covering the nipples and the papillary layer of the border of the lips]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


(ep?i-the'le-um) ('le-a) plural.epithelia [ epi- + Gr. thele, nipple, teat + -ium (2)]
Enlarge picture
The layer of cells forming the epidermis of the skin and the surface layer of mucous and serous membranes. The cells rest on a basement membrane and lie in close approximation with little intercellular material between them. They are devoid of blood vessels. The epithelium may be simple, consisting of a single layer, or stratified, consisting of several layers. Cells making up the epithelium may be flat (squamous), cube-shaped (cuboidal), or cylindrical (columnar). Modified forms of epithelium include ciliated, pseudostratified, glandular, and neuroepithelium. The epithelium may include goblet cells, which secrete mucus. Stratified squamous epithelium may be keratinized for a protective function or abnormally keratinized in pathological response. Squamous epithelium is classified as endothelium, which lines the blood vessels and the heart, and mesothelium, which lines the serous cavities. Epithelium serves the general functions of protection, absorption, and secretion, and specialized functions such as movement of substances through ducts, production of germ cells, and reception of stimuli. Its ability to regenerate is excellent; it may replace itself as frequently as every 24 hr. See: illustration; skinepithelial (-al), adjective

ciliated epithelium

Epithelium with hairlike processes on the surface that wave actively only in one direction. This type is present in the respiratory tract and fallopian tubes.

columnar epithelium

Epithelium composed of cylindrical cells.

cuboidal epithelium

Epithelium consisting of cube-shaped or prismatic cells with height about equal to their width.

germinal epithelium

1. Epithelium that covers the surface of the genital ridge of the urogenital folds of an embryo. It gives rise to the seminiferous tubules of the testes and the surface layer of the ovary. It was once thought to produce the germ cells (spermatozoa and ova).
2. The epithelium that covers the surface of a mature mammalian ovary.

glandular epithelium

Epithelium consisting of secretory cells.

junctional epithelium

A band of nonkeratinized stratified squamous epithelium that attaches both to the gingiva (on one side) and the crown of the tooth (on the other). Synonym: epithelial attachment; gingival cuff

laminated epithelium

Stratified epithelium.

mesenchymal epithelium

Squamous epithelium that lines the subarachnoid and subdural cavities, the chambers of the eye, and the perilymphatic spaces of the ear.

pavement epithelium

Epithelium consisting of flat, platelike cells in a single layer.

pigmented epithelium

Epithelium containing pigment granules.

pseudostratified epithelium

Epithelium in which the bases of cells rest on the basement membrane but the distal ends of some do not reach the surface. Their nuclei lie at different levels, giving the appearance of stratification.

reduced enamel epithelium

Combined epithelial layers of the enamel organ, which form a protective layer over the enamel crown as it erupts and then become the primary epithelial attachment surrounding the tooth.

squamous epithelium

The flat form of epithelial cells.

stratified epithelium

Epithelium with the cells in layers; mitosis takes place in the lowest layer. Synonym: laminated epithelium

sulcular epithelium

The nonkeratinized epithelium that lines the gingival sulcus.

transitional epithelium

A form of stratified epithelium in which the cuboidal cells adjust to mechanical changes such as stretching and recoiling. This type of tissue is found only in the urinary system (renal pelvis, ureter, bladder, and a part of the urethra).
Medical Dictionary, © 2009 Farlex and Partners


The non-stick coating cell layer for all surfaces of the body except the insides of blood and lymph vessels. Epithelium may be single-layered, or ‘stratified’ and in several layers, with the cells becoming flatter and more scaly towards the surface, as in the skin. It may be covered with fine wafting hair-like structures (cilia), as in the respiratory tract, and it may contain mucus-secreting ‘goblet’ cells. See also ENDOTHELIUM and EPIDERMIS.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
Epithelium (1)click for a larger image
Fig. 153 Epithelium (1) . Types of epithelium.


  1. (in animals) a layer of covering cells lying on a basement membrane that is called simple epithelium when one cell thick and compound epithelium when several cells thick, and usually covers connective tissue embryologically derived from the ECTODERM. The cells sometimes have a secretory function and are held together by a cementing substance to form a sheet. Their shape gives rise to names descriptive of the cells, e.g. columnar, cubical, squamous (see Fig. 153 ). Where the epithelium is more than one cell thick it is described as stratified. Similar cells can be derived from MESODERM and are referred to as mesothelium when lining the COELOM, and as ENDOTHELIUM when lining blood vessels.
  2. (in plants) a layer of cells lining cavities and secretory canals, for example, resin canals.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005


Cells composing the lining of an organ.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


, pl. epithelia (ep'i-thē'lē-ŭm, -ă) [TA]
The purely cellular avascular layer covering all free surfaces, cutaneous, mucous, and serous, including the glands and other structures derived therefrom.
[G. epi, upon, + thēlē, nipple, a term applied originally to the thin skin covering the nipples and the papillary layer of the border of the lips]
Medical Dictionary for the Dental Professions © Farlex 2012
References in periodicals archive ?
As the epithelial layer is a tight pack of cells, the surrounding medium for these scattering centers is intracellular medium (cell cytoplasm) with its refractive index [n.sub.cell] lying between 1.35 and 1.38 [11].
Those kept at 14[degrees]C had a significantly thicker stomach epithelial layer than those at 22[degrees]C, and this finding is consistent with studies conducted on fish species.
It could be suggested that even with a decrease in the stomach epithelial layer at 22[degrees]C, the absorptive capacity was maintained and was adequate to provide the nutrients required for reasonable levels of growth at the warmer temperature.
The significant reduction of inflammatory-destructive changes takes place in the wall of gall bladders: the inflammatory infiltration, edema and stasis reduced as well as formation of thrombi in the vessel lumens, the integrity of the epithelial layers in the mucosa were restored too.
For each data point, images of both oral and aboral epithelial layers of five sections were captured with an 8-bit CCD Sony XC-75 video camera and accumulated using a frame accumulation program written by Dr.
1) There is a hyperkeratosis of the upper epithelial layer that represents an altered pattern of keratin expression in the squamous epithelial cells.
CD8+ cells appeared inside the epithelium of patients with recurrent maxillary sinusitis due to the cytotoxicity of destructed cells accompanied by degeneration of epithelial layer tissue deformation and damages of mucociliary transport functions.
These changes result in the phenotypic conversion from the normal, stratified epithelial layers of the esophagus to a columnar epithelial phenotype, and the appearance of goblet cells within the lining of the esophagus.
Interestingly, at 96 hpf, Bves was found in the cell membranes of all epithelial layers of the eye; however, the retina exhibited the strongest expression.
Generally speaking, within 2 months of surgery, all flaps and epithelial layers had become smooth and healthy and had covered all surfaces.
During this last stage of embryogenesis, two epithelial layers separated by a basement membrane are formed; these closely resemble the cell layers of the adult animal.
Type A secretory cells exists mainly in the epithelial layer, with typical goblet form and a length of approximately 7 [micro]m.