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epithelium[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.
highly discernible stratified epithelium with large, polyploid superficial cells that are dome shaped when relaxed but broad and flattened when distended; occurs in the calyces of the kidney, and in the ureter and bladder.
a form of stratified epithelium found characteristically in the mucous membrane of ureter and bladder; in the contracted condition it consists of many cell layers, whereas in the stretched condition fewer layers can be distinguished.
tran·si·tion·al ep·i·the·li·um(tran-zish'ŭn-ăl ep'i-thē'lē-ŭm)
A highly distensible pseudostratified epithelium with large polyploid superficial cells that are cuboidal in the relaxed state but broad and squamous in the distended state; occurs in the kidney, ureter, and bladder.