<P> Simple epithelium is a single layer of cells with every cell in direct contact with the basement membrane that separates it from the underlying connective tissue . In general, it is found where absorption and filtration occur . The thinness of the epithelial barrier facilitates these processes . </P> <P> In general, simple epithelial tissues are classified by the shape of their cells . The four major classes of simple epithelium are: (1) simple squamous; (2) simple cuboidal; (3) simple columnar; (4) pseudostratified . </P> <Dl> <Dd> (1) simple squamous; which is found lining areas where passive diffusion of gases occur . e.g. skin, walls of capillaries, linings of the pericardial, pleural, and peritoneal cavities, as well as the linings of the alveoli of the lungs . </Dd> <Dd> (2) simple cuboidal: these cells may have secretory, absorptive, or excretory functions . examples include small collecting ducts of kidney, pancreas, and salivary gland . </Dd> <Dd> (3) simple columnar; cells can be secretory, absorptive, or excretory; Simple columnar epithelium can be ciliated or non-ciliated; ciliated columnar is found in the female reproductive tract and uterus . Non-ciliated epithelium can also possess microvilli . </Dd> <Dd> (4) pseudostratified columnar epithelium; can be ciliated or non-ciliated . The ciliated type is also called respiratory epithelium as it is almost exclusively confined to the larger respiratory airways of the nasal cavity, trachea and bronchi . </Dd> </Dl> <Dd> (1) simple squamous; which is found lining areas where passive diffusion of gases occur . e.g. skin, walls of capillaries, linings of the pericardial, pleural, and peritoneal cavities, as well as the linings of the alveoli of the lungs . </Dd>

How is the structure of the following kinds of epithelium related to their functions
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