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Epithelial Tissue
Epithelial tissue (also epithelium) occurs throughout the body. It is of two basic types: (1) that forming the epidermis; (2) that forming the surfaces of the mucous and serous membranes. It covers the body and also lines body cavities and hollow organs. It is also one of the prominent tissue types in glands. It can have various functions, including diffusion, protection, absorption, secretion, excretion, filtration, and sensory reception.
In shape, epithelial cells may be squamous, columnar, or cuboidal (see figure). There can be a single layer (simple epithelium) or multiple layers (stratified epithelium).
Epithelial cells fit tight together with little intercellular space. Epithelium, because it forms coverings and linings, has one free surface not in contact with other cells. On the opposite surface, the epithelium is attached to underlying connective tissue by a non-cellular basement membrane, composed of carbohydrates and proteins.
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