The mucosa, also known as the tunic or mucous membrane, consists of a lining epithelium associated with a connective tissue called lamina propria. It is responsible for the internal lining of moist body cavities that maintain contact with the external environment such as the mouth, intestine, bladder, respiratory tract and urogenital tract. Because they are subject to microbial invasions, the mucous membranes in these regions present as non-specific immunity and have lymphocyte accumulations in the form of lymph nodes associated with diffuse lymphatic tissue. In some regions, such as the ileum, the lymphatic tissue is organized into well-structured organs called Meyer's tonsils and plaques.
