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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.
The mucosa is composed of one or more layers of epithelial cells that secrete mucus, and an underlying lamina propria of loose connective tissue. [1] The type of cells and type of mucus secreted vary from organ to organ and each can differ along a given tract. [2] [3]
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]
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.
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.
A basal cell is a general cell type that is present in many forms of epithelial tissue throughout the body. Basal cells are located between the basement membrane and the remainder of the epithelium, effectively functioning as an anchor for the epithelial layer and an important mechanism in the maintenance of intraorgan homeostasis.
It provides an impenetrable barrier between the lumen and the bloodstream, so as not to allow the bloodstream to reabsorb harmful wastes or pathogens. [4] All transitional epithelial cells are covered in microvilli and a fibrillar mucous coat. [3] The epithelium contains many intimate and delicate connections to neural and connective tissue.
Exocrine glands are glands that secrete substances onto an epithelial surface by way of a duct. [1] Examples of exocrine glands include sweat , salivary , mammary , ceruminous , lacrimal , sebaceous , prostate and mucous .