what is epithelial tissue ? also called as ?
Answers
Explanation:
Epithelial tissues are widespread throughout the body. They form the covering of all body surfaces, line body cavities and hollow organs, and are the major tissue in glands. Epithelial cells may be squamous, cuboidal, or columnar in shape and may be arranged in single or multiple layers. ...
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Answer:
Epithelial Tissue is one of the four types of tissue (epithelial, muscular, connective, and nervous) in animals which consists of closely aggregated polyhedral cells adhering firmly to one another, forming cellular sheets that line the interior of hollow organs and cover the body surface. An epithelial tissue or epithelium (plural is epithelia) consists of cells arranged in continuous sheets, in either single or multiple layers.
Characteristics of Epithelial Tissue
Even though epithelial tissue present in different parts of the body might differ in structure and function, they all have some common characteristics.
Some of these characteristics are given below:
Shape and Size:
The shapes and sizes of epithelial cells are variable, ranging from tall columnar to cuboidal to low squamous.
The cell’s size and morphology are generally based on their function.
Polarity:
Epithelial cells generally show polarity, with organelles and membrane proteins distributed unevenly within the cell.
The apical (free) surface of an epithelial cell is present towards the body surface, the body cavity, the lumen of an internal organ, or a gland duct that receives cell secretions. Apical surfaces may contain cilia or microvilli.
The lateral surfaces of an epithelial cell, facing the adjacent cells on either side, may contain intercellular adhesion and other junctions.
The basal surface of an epithelial cell adheres to extracellular materials such as the basement membrane, which is an inert connective tissue made by the epithelial cells themselves.
Basement Membrane
The basement membrane is a thin extracellular layer that commonly consists of two layers, the basal lamina, and the reticular lamina.
The basal lamina is closer to and secreted by the epithelial cells and contains proteins like laminin and collagen as well as some glycoproteins and proteoglycans.
The reticular lamina is closer to the connective tissue, present underneath, and contains collagen protein produced by connective tissue cells called fibroblasts.
Intercellular Adhesion and Other Junctions
Several membrane-associated structures provide adhesion and communication between cells.
Tight junctions, also called zonulae occludens, are the most apical of the junctions that form a band completely encircling each cell.
The second type of junction is the adherens junction or zonula adherens, which also encircles the epithelial cell, usually immediately below the tight junction.
Another anchoring junction is the desmosome or macula adherens which are disc-shaped structures at the surface of one cell that matches with identical structures at an adjacent cell surface.
Gap junctions mediate intercellular: communication rather than adhesion or occlusion between cells.
Avascular:
Epithelial tissue is avascular, relying on the blood vessels of the adjacent connective tissue to bring nutrients and remove wastes.
The exchange of substances between epithelial tissue and connective tissue occurs by diffusion.
Innervated:
Epithelial tissue is innervated; that is, it has its own nerve supply.
Renew and Repair:
Epithelial cells have a high rate of cell division which allows the epithelial tissue to continually renew and repair itself by sloughing off dead or injured cells and replacing them with new ones.
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