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Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis , the outermost layer of the skin . Epithelial ( mesothelial ) tissues line the outer surfaces of many internal organs , the corresponding inner surfaces of body cavities , and the inner surfaces of ...
Simple squamous epithelium falls under the physiological category of exchange epithelium due to its ability to rapidly transport molecules across the tissue layer. To facilitate this movement, some types of simple squamous epithelium may have pores between cells to allow molecules to move through it, creating a leaky epithelium.
The cells in the respiratory epithelium are of five main types: a) ciliated cells, b) goblet cells, c) brush cells, d) airway basal cells, and e) small granule cells (NDES) [6] Goblet cells become increasingly fewer further down the respiratory tree until they are absent in the terminal bronchioles; club cells take over their role to some extent here. [7]
A stratified squamous epithelium consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane.Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity.
Simple columnar epithelium is a single layer of columnar epithelial cells which are tall and slender with oval-shaped nuclei located in the basal region, attached to the basement membrane. In humans, simple columnar epithelium lines most organs of the digestive tract including the stomach , and intestines .
Functions of epithelial tissue: The principle function of epithelial tissues are covering and lining of free surface; The cells of the body's surface form the outer layer of skin. Inside the body, epithelial cells form the lining of the mouth and alimentary canal and protect these organs. Epithelial tissues help in the elimination of waste.
Pseudostratified columnar epithelium is a type of epithelium that, though comprising only a single layer of cells, has its cell nuclei positioned in a manner suggestive of stratified columnar epithelium.
Cell junctions are especially abundant in epithelial tissues. Combined with cell adhesion molecules and extracellular matrix , cell junctions help hold animal cells together. Cell junctions are also especially important in enabling communication between neighboring cells via specialized protein complexes called communicating (gap) junctions .