Epiteelikudoksiin

Epiteelikudoksiin is a term derived from Estonian, meaning "epithelial cells" or "epithelial tissue." In biological contexts, it refers to the cellular layer that forms the lining of internal organs, body cavities, and the surface of the skin. This tissue plays a crucial role in protection, secretion, absorption, and excretion.

Epithelial cells are characterized by their close arrangement, forming continuous sheets that cover all exposed surfaces of the body and line internal passages. They exhibit polarity, meaning they have distinct apical and basal surfaces, with different structures and functions. The apical surface often faces a lumen or the external environment and may possess specialized structures like cilia or microvilli. The basal surface is attached to a basement membrane, a layer of extracellular matrix that anchors the epithelium.

There are various types of epithelial tissue, classified based on their cell shape (squamous, cuboidal, columnar) and the number of cell layers (simple, stratified). Simple epithelia consist of a single layer of cells and are typically involved in absorption, secretion, and filtration. Stratified epithelia have multiple layers of cells and are primarily for protection in areas subject to abrasion. Pseudostratified columnar epithelium, while appearing stratified, is a single layer of cells where nuclei are at different levels. Transitional epithelium is found in organs that undergo stretching, such as the bladder, and has cells that can change shape.

Epithelial tissue is avascular, meaning it lacks blood vessels, and nutrients are supplied by diffusion from underlying connective tissues. It has a high regenerative capacity, allowing for continuous repair and replacement of cells. Disorders affecting epithelial tissue can range from skin conditions like eczema to more serious diseases involving internal linings, such as inflammatory bowel disease or certain cancers.