A mucous membrane is a layer of epithelial tissue which lines an area of the body which comes into contact with air. Mucous membranes are moist because of the presence of glands which secrete a thick fluid known as mucus, and they are important for a number of bodily functions. Mucous membranes line the urogenital tract, digestive tract, and respiratory tract, with one of the more well known mucous membranes being the lining of the interior of the nose.
The moisture found in a mucous membrane acts to protect the body by creating a barrier and preventing the inside of the body from drying out. Mucus also traps pathogens, dirt, and particulate matter so that they can be sequestered and eliminated by the body. The nose is particularly famous for this, using mucus as a barrier between many harmful substances and the respiratory tract. Some sections of mucous membrane also have small hairs known as cilia which act as traps, and can move to push things across the surface of the membrane.