Tissue that lines body passages and body cavities which are exposed to the air, such as inside the mouth or nose, and around the eyes. Changes in mucous membranes are sometimes a sign of health problems. In a dehydrated animal Mucous membranes are abnormally dry if an animal is dehydrated, pale if an animal is anaemic or in shock, yellowish when the liver malfunctions.
Any tissue lining body cavities and canals which come in contact with the air, and kept moist by secretions of various types of glands (e.g., inside the mouth).
Lubricating membranes lining the internal surfaces of body cavities, such as the mouth, digestive tract, respiratory tract, and urinary tract.