A mucous membrane, also called a mucosa, is a soft, pink skin-like layer that lines many of the cavities and tubes in the body, including the respiratory tract, gastrointestinal tract, the urinary and genital passages, and eyelids. Mucous membranes secrete a fluid containing mucus which keeps body structures moist and well-lubricated. The fluid is produced and released on to the surface of the mucous membrane by millions of specialized cells, called goblet cells, situated within the membrane.