fiber /fī″bər/ , 1. a long, filmlike, threadlike, acellular structure found in plant and animal tissues. Plant fibers usually consist of structural carbohydrates such as cellulose in cell walls. Composed of repeating glucose units in long, single strands, cellulose cannot be digested by enzymes in the human intestine. Other plant fiber components include hemicellulose and pectin. Animal fibers are composed mainly of the protein collagen, which forms elastic threads of loose connective tissue in skin and other organs. See also dietary fiber. 2. a skeletal muscle cell. 3. the axon of a nerve cell.
