epitheliumCell

epitheliumCell is a term used to describe the epithelial cell, a basic cell type that forms the epithelium, the tissue that lines surfaces and cavities of the body. Epithelial cells are polarized and organized into sheets that cover external surfaces and line internal cavities such as the mouth, gut, airways, and ducts. They are typically avascular and receive nutrients by diffusion from the underlying connective tissue; many epithelia renew themselves continuously through resident stem or progenitor cells in the basal layer.

Epithelial tissues are classified by arrangement and shape. Simple epithelia consist of a single cell layer, while stratified epithelia have multiple layers. Cell shapes include squamous (flat), cuboidal, and columnar; specialized forms include pseudostratified ciliated columnar epithelium and transitional epithelium. The apical surface may bear microvilli for absorption or cilia for movement; the basolateral surface interfaces with neighboring cells and the basement membrane.

Epithelial cells connect via intercellular junctions such as tight junctions, adherens junctions, desmosomes, and gap junctions. They rest on the basement membrane, a thin extracellular matrix that anchors them to connective tissue. Functions include protection, selective permeability, secretion, and sensation. Examples include keratinocytes in the skin, absorptive enterocytes in the intestine, goblet cells that secrete mucus, and ciliated cells in the respiratory tract.

Clinical notes: epithelial cells give rise to carcinomas, a common cancer type. Epithelial tissues exhibit regenerative capacity; dysplasia and metaplasia may occur in response to injury. Understanding epithelial cell biology informs fields from physiology to pathology and organ function.