Editing Human body (section)

====Cells====
Cells that line surfaces exposed to the outside world or gastrointestinal tract ([[Epithelium|epithelia]]) or internal cavities ([[endothelium]]) come in numerous shapes and forms – from [[Epithelium|single layers of flat cells]], to cells with small beating hair-like [[Cilium|cilia]] in the lungs, to column-like cells that line the [[stomach]]. Endothelial cells are cells that line internal cavities including blood vessels and glands. Lining cells regulate what can and cannot pass through them, protect internal structures, and function as sensory surfaces.{{sfn|Gray's Anatomy|2008|p=27}}