• A layer of cells which lines organs and structures in the body, protecting or enclosing them.
  Harvard Dictionary of Health Terms
  Harvard Medical Publishing, 2011
• A thin layer of tissue that covers organs, glands, and other structures within the body.
  NCI Dictionary of Cancer Terms
  U.S. National Cancer Institute, 2021
• The avascular cellular layers that cover body surfaces and cavities and may form glands.
  NCI
  U.S. National Cancer Institute, 2021
• The layers of EPITHELIAL CELLS which cover the inner and outer surfaces of the cutaneous, mucus, and serous tissues and glands of the body.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2025
• Thin layer of tissue that covers the inner or outer surfaces of organs, glands, and other structures within the body.
  CRISP Thesaurus
  National Institutes of Health, 2006
• Tissue, which consists of one or more layers of epithelial cells and a basement membrane; it covers the external surface of the body and lines the internal surfaces of the anatomical structures. Examples: simple squamous epithelium, glandular cuboidal epithelium, transitional epithelium, myoepithelium.
  Digital Anatomist
  University of Washington, 2003
• (portion of epithelium) Portion of tissue, which consists of one or more layers of epithelial cells and a basement membrane; it covers the external surface of the body and lines the internal surfaces of the anatomical structures. Examples: simple squamous epithelium, glandular cuboidal epithelium, transitional epithelium, myoepithelium.
  Foundational Model of Anatomy
  University of Washington, 2017
• Epithelium, in anatomy, layer of cells closely bound to one another to form continuous sheets covering surfaces that may come into contact with foreign substances. Epithelium occurs in both plants and animals. In animals, outgrowths or ingrowths from these surfaces form structures consisting...
  Encyclopedia Britannica
  Encyclopedia Britannica, Inc., 2025