epithelium defined in 1951 yearepithelium - epithelium;
epithelium - (Zool.). Sheet or tube of firmly coherent cells, with minimal material between the cells. (The term is, however, often not applied to such sheets or tubes when they have been embryonically derived from mesoderm, e.g. lining of blood-vessels (endothelium) or of coelom (mesothelium).) Lines cavities and tubes and covers exposed surfaces of body; one surface of epithelium being therefore free, other resting usually on connective tissue. Its cells are frequently secretory, and secretory part of most glands is made of epithelium. Epithelia are classified according to height of cell (dimension at right angles to extension of sheet) relative to breadth, into columnar, cubical, and squamous (in order of diminishing relative height) and according to whether sheet is one cell thick (simple) or many (stratified). Examples of non-epithelial tissues are connective tissue, muscle, nervous tissue. (Bot.). Layer of cells lining schizogenously formed secretory canals and cavities, e.g. in resin canals of pine.
near epithelium in Knolik
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