epitheliumthe

Epithelium is a cellular tissue that lines surfaces and forms glands. The term "epitheliumthe" does not correspond to a recognized anatomical entity in standard histology and is likely a misspelling or typographical variant of epithelium. When encountered, it should be corrected to the standard term epithelium.

Epithelium consists of tightly packed cells with minimal extracellular matrix and a basement membrane that anchors it to underlying connective tissue. The cells show polarity: an apical surface facing a lumen or external environment, a lateral surface with intercellular junctions, and a basal surface attached to the basement membrane. Many epithelia have microvilli or cilia on the apical face.

Classification is based on the number of cell layers and on cell shape. Simple epithelia have a single layer: squamous (flattened), cuboidal (cube-shaped), or columnar (tall). Pseudostratified epithelia appear multilayered but all cells touch the basement membrane. Stratified epithelia include squamous, cuboidal, and columnar types in multiple layers.

Functions include protection, selective absorption and secretion, filtration, diffusion, and sensory reception. Glandular epithelia produce secretions such as enzymes, mucus, and hormones. Epithelial tissues line internal organs (gastrointestinal tract, respiratory tract), form ducts and glands, and cover body surfaces.

Development and pathophysiology: epithelia arise from all germ layers and continually renew through stem cell proliferation. Damage can be repaired by regeneration, though chronic injury or metaplasia can lead to pathological changes. Epithelial origin cancers, particularly carcinomas, are among the most common cancers.

Etymology and usage: epithelium derives from Greek and is standard; epitheliumthe is not recognized and should be corrected when encountered.