Definition of "epithelium" [ep•i•the•li•um]

• Membranous tissue composed of one or more layers of cells separated by very little intercellular substance and forming the covering of most internal and external surfaces of the body and its organs. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Vitamin A promotes a healthy intestinal epithelium, which is important for optimal absorption of nutrients, and it also promotes strong joints."
• "People with IBS experience some dysfunction of the immune and nervous systems that regulate the lining of the bowel; this lining called the epithelium is what regulates the flow of fluids into and out of the intestines."
• "It was thought that macrophage cells with TLRs didn't sense beneficial or neutral bacteria in part because such bacteria were protected by the lining of the gut and other organs, called the epithelium, which was believed to keep macrophage cells on one side and bacteria on the other."