epiteli

Epiteli are a family of tissues that line body surfaces, form glands, and contribute to barrier, secretion, and absorption functions. In Italian anatomy, epitelio is the singular form and epiteli its plural. Epithelial tissues are characteristically avascular and organized as tightly joined cells arranged in sheets, all resting on a basement membrane. They exhibit apical and basal polarity and are supported by a thin extracellular matrix.

Epithelial tissues are commonly classified by arrangement into simple epithelia (one cell layer) and stratified epithelia (two or more layers), with pseudostratified epithelia appearing to have multiple layers due to cell height differences. By cell shape, epithelia are described as squamous, cuboidal, or columnar, with transitional epithelia able to stretch, such as in the urinary bladder.

Functions include protection (skin, mucosal surfaces), selective absorption (intestines), secretion (glands, goblet cells), ion and water transport (kidney tubules), and sensation (sensory epithelia). Some epithelia possess specialized features such as cilia, microvilli, or mucus-producing cells, which enhance their surface interactions with the environment.

Common locations include skin (stratified squamous epithelium), the lining of the gut (simple columnar), airways (pseudostratified ciliated columnar with goblet cells), kidneys (simple cuboidal), and the bladder (transitional epithelium). The integrity of epithelia is maintained by cell junctions, such as tight junctions, adherens junctions, desmosomes, and gap junctions, and by the basement membrane.

Renewal and repair depend on resident stem cells in the basal layer, enabling rapid turnover in many tissues. Epithelial abnormalities can lead to diseases, most notably carcinomas arising from epithelial cells. Epithelia also form glands and contribute to organ-specific functions such as secretion, filtration, and sensory perception.