Epithelial tissue

Epithelial Tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue, and nervous tissue. It is a tissue that lines the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs.

Structure

Epithelial tissue is composed of cells laid together in sheets with the cells tightly connected to one another. Epithelial layers are avascular, but innervated. Epithelial cells have two surfaces that differ in both structure and function. One surface is usually exposed to the internal or external environment, while the other is attached to a basement membrane. This membrane serves as a base upon which the cells can grow and regenerate after injuries.

Functions

Epithelial tissues have several functions, which include protection against abrasion, radiation damage, chemical stress and invasion by pathogens. A single organ can have different types of epithelial tissue based on the substances to which different surfaces are exposed. Epithelial tissue also serves to both selectively absorb substances into the body and help filter out toxic substances, and to provide sensory input.

Types

There are several different types of epithelial tissues which are classified by the shape of their cells and the number of layers they form. The three principal shapes associated with epithelial cells are—squamous, cuboidal and columnar.

Squamous Epithelium

Squamous epithelium has cells that are wider than their height (flat and scale-like). This is a single layer of cells with the appearance of thin scales. It is found in areas of the body where rapid diffusion is required.

Cuboidal Epithelium

Cuboidal epithelium consists of cube-shaped cells. This type of epithelium is found in areas of the body where secretion and absorption occur.

Columnar Epithelium

Columnar epithelium forms a single layer of columnar cells that fit closely together. It is found in areas of the body where absorption and secretion are primary functions.

See Also

• Connective tissue
• Muscle tissue
• Nervous tissue

Epithelial tissue Resources
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