mucous membrane

:  a moist membranous layer rich in mucous glands that lines body passages and cavities (as of the digestive, respiratory, and genitourinary tracts) which connect directly or indirectly with the exterior, that functions in protection, support, nutrient absorption, and secretion of mucus, enzymes, and salts, and that is composed of epithelium supported below by the lamina propria and sometimes by the muscularis mucosae—called also mucosa; compare serous membrane