Epithelialer

Epithelialer is not a widely established term in English, but in some texts it functions as a noun referring to an epithelial cell or as an adjective meaning related to epithelium. The concept it points to is the epithelium, a tissue that lines surfaces, cavities, and glands in animals and humans.

Epithelial tissue covers body surfaces and forms the lining of internal compartments such as the skin, the airways, the digestive tract, and the ducts of glands. Epithelial cells are tightly joined and sit on a basement membrane that separates them from underlying connective tissue. The cells exhibit polarity, with an apical (top) surface often specialized for contact with the environment (such as cilia or microvilli) and a basal surface anchored to the basement membrane. Junctional complexes, including tight junctions, adherens junctions, and desmosomes, help maintain integrity and selective permeability.

The epithelium is classified by both cell shape and layering. Simple epithelia consist of a single cell layer and include squamous, cuboidal, and columnar types; stratified epithelia have multiple cell layers and predominantly provide protection. Transitional epithelium is specialized for stretch, as seen in the urinary bladder. Glandular epithelia arise from epithelial tissues and form secretory units in exocrine and endocrine glands.

Functions of epithelial tissue are diverse. They provide protection against mechanical and chemical injury, regulate exchange of substances, facilitate absorption and secretion, participate in sensation, and form barriers against pathogens. Epithelial turnover is high in many tissues, with renewal driven by stem or progenitor cells in the basal layer.

Clinical relevance includes the role of epithelium in barrier function and in carcinomas, which arise from epithelial cells. In pathology, epithelial alterations such as dysplasia can indicate precancerous changes or disease progression.