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SIMPLE EPITHELIA

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 These epithelia, also called unilaminar epithelia, consist of only a single layer of cells. Each cell of this epithelial layer has a basal surface which rests on the basement membrane, and a free surface which faces the cavity (or lumen) of an organ' or a body part. Simple Epithelia A simple epithelium consists of only a single layer of cells. Each cell has a free surface and a basal surface which rests on the basement membrane. The lateral margins of the adjacent cells are closely apposed and are held together by cell junctions; therefore, in a surface view, the cells appear to form a mosaic. According to the shape of their component cells, the simple epithelia are further classified into the following three types:
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SIMPLE SQUAMOUS EPITHELIUM

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                The simple squamous epi variety of epithelium consists of a single layer of thin flat cells which are roughly polygonal in outline. The free surface of each flat cell faces a cavity or the lumen of a tubular structure, while the basal surface rests on a basement membrane, The cells have serrated or wavy margins and the adjacent cells fit closely together to form a continuous sheet. Each cell contains a flattened nucleus located in the center of the cell. Presence of the nucleus in the central region of the flat cell causes the plasma membranes above and below to bulge slightly. Simple squamous epithelium                 On surface view the closely fitting polygonal cells appear like a mosaic. Sections made perpendicular to the epithelial sheet show that in profile (ie, in side view) the individual cells give fusiform (spindle-shaped) appearance because the central region of each cel...
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PSEUDOSTRATIFIED COLUMNAR EPITHELIUM

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      This type of epithelium consists of tall cells and short cells. All cells of the pesudostratified columnar epithelium rest on the basement membrane but all of them do not reach the free surface of the epithelium. Only the tall columnar cells extend through the entire thickness of the epithelium. Each of these cells has a wider part which reaches the free surface of the epithelium and a narrow and slender basal part which passes downward to rest on the basement membrane. The short cells also called basal cells, lie between the columnar cells. The basal cells are conical in shape having a broad base which rests on the basal lamina and a tapering upper part which terminates between the columnar cells and does not reach the free surface of the epithelium. As the cell nuclei are located in the wider parts of both types of the cells of the pseudostratified columnar epithelium they are present in the apical part of the tall cells and basal parts of the short cells. The nu...
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