Epithelia

Part of speech: noun

Definitions

1. A type of tissue composed of layers of cells that cover body surfaces and line cavities
2. A cellular structure that serves to protect, absorb, and secrete, forming the outer layer of organs and glands
3. A collection of closely packed cells that form protective barriers and play roles in sensation and secretion across various bodily systems

Etymology: "Epithelia" is the plural of "epithelium," so the word's origin lies in the singular form, which comes from New Latin, the scholarly Latin used by early modern and modern scientists to coin technical terms. Its parts are "epi-," meaning "upon" or "on top of," and "thel-," from the Greek "thēlē," meaning "nipple" or "teat," with the Latin suffix "-ium" completing the form. Put together, the name describes a tissue sitting upon a surface, the way a nipple rises from skin. The image is a useful one: epithelial tissue forms the outer skin of the body and the linings of organs and cavities, always resting on a layer of connective tissue beneath it. The word was built by anatomists who needed a name for these sheet-like coverings, and they reached back to classical Greek for the building blocks rather than for any ancient term for the tissue itself, which the Greeks and Romans did not have.