In biology and medicine, epithelium is a tissue composed of layers of cells that line the cavities and surfaces of structures throughout the body. It is also the type of tissue of which many glands are formed. Epithelium lines both the outside (skin) and the inside cavities and lumen of bodies. The outermost layer of our skin is composed of dead stratified squamous, keratinized epithelial cells.
Mucous membranes lining the inside of the mouth, the oesophagus, and part of the rectum are lined by nonkeratinized stratified squamous epithelium. Other, open to outside body cavities are lined by simple squamous or columnar epithelial cells.
Other epithelial cells line the insides of the lungs, the gastrointestinal tract, the reproductive and urinary tracts, and make up the exocrine and endocrine glands. The outer surface of the cornea is covered with fast-growing, easily-regenerated epithelial cells.
Functions of epithelial cells include secretion, absorption, protection, transcellular transport, sensation detection, and selective permeability.
Endothelium (the inner lining of blood vessels, the heart, and lymphatic vessels) is a specialized form of epithelium. Another type, Mesothelium, forms the walls of the pericardium, pleurae, and peritoneum.
Mucous membranes lining the inside of the mouth, the oesophagus, and part of the rectum are lined by nonkeratinized stratified squamous epithelium. Other, open to outside body cavities are lined by simple squamous or columnar epithelial cells.
Other epithelial cells line the insides of the lungs, the gastrointestinal tract, the reproductive and urinary tracts, and make up the exocrine and endocrine glands. The outer surface of the cornea is covered with fast-growing, easily-regenerated epithelial cells.
Functions of epithelial cells include secretion, absorption, protection, transcellular transport, sensation detection, and selective permeability.
Endothelium (the inner lining of blood vessels, the heart, and lymphatic vessels) is a specialized form of epithelium. Another type, Mesothelium, forms the walls of the pericardium, pleurae, and peritoneum.
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