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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 blood vessels.
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.
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.
Transitional epithelium also functions as a barrier between the lumen, or inside hollow space of the tract that it lines and the bloodstream. To help achieve this, the cells of transitional epithelium are connected by tight junctions, or virtually impenetrable junctions that seal together to the cellular membranes of neighboring cells.
Most of the barrier functions of the epidermis localize to this layer. [12] clear/translucent layer (stratum lucidum, only in palms and soles) This narrow layer is found only on the palms and soles. The epidermis of these two areas is known as "thick skin" because with this extra layer, the skin has 5 epidermal layers instead of 4.
The principal function of this basolateral membrane is to take up metabolic waste products into the epithelial cell for disposal into the lumen where it is transported out of the body as urine. A secondary role of the basolateral membrane is to allow the recycling of desirable substrates, such as glucose , that have been rescued from the lumen ...
Simple columnar epithelium is further divided into two categories: ciliated and non-ciliated (glandular). The ciliated part of the simple columnar epithelium has tiny hairs which help move mucus and other substances up the respiratory tract.