Layer of epithelial tissue with a thin underlying layer of connective tissue (the lamina propria) that lines many body cavities, including the gut, respiratory passages, and tubular organs; it secretes, and is covered in, mucus.
Source: PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 781 (https://doi.org/10.1515/pac-2015-1202)