Epithelia, also known as epithelial tissue, refer to one of the major types of animal tissues that cover the surfaces of organs, line body cavities, and form glands. Epithelial tissue is composed of tightly packed cells that are closely joined together without any surrounding intercellular substance, providing a protective barrier for underlying tissues.
Epithelia play crucial roles in various bodily functions, including protection against physical, chemical, and biological factors, absorption and secretion of substances, and sensory reception. They are classified based on their shape and arrangement of cells. Regarding cellular shape, there are three main types: squamous (flat and scale-like), cuboidal (cube-shaped), and columnar (elongated and column-like).
Epithelia can be further categorized into different arrangements based on the number of cell layers they possess. These include simple epithelium (single layer of cells), stratified epithelium (multiple layers of cells), and pseudostratified epithelium (appearing stratified but composed of a single layer). The arrangement often reflects the specific functions performed by the epithelial tissue.
Found in numerous organs, such as the skin, respiratory and digestive tracts, and glands, epithelia are characterized by the presence of specialized structures called apical surfaces, lateral surfaces, and basal surfaces. The apical surface is exposed to the external environment or internal cavities, while the basal surface attaches the epithelium to underlying connective tissues. Lateral surfaces are in contact with neighboring cells.
Overall, epithelia are essential for maintaining tissue integrity, selective permeability, and contributing to organs' proper functioning. Their diverse characteristics and arrangements allow them to adapt and serve specific functions throughout the body.
