The mucous membranes (or mucosae; singular mucosa) are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line various body cavities that are exposed to the external environment and internal organs. It is at several places continuous with skin: at the nostrils, the lips, the ears, the genital area, and the anus. The sticky, thick fluid secreted by the mucous membranes and gland is termed mucus. The term mucous membrane refers to where they are found in the body and not every mucous membrane secretes mucus.
Body cavities featuring mucous membrane include most of the respiratory system. The glans penis (head of the penis) and glans clitoridis and the inside of the prepuce (foreskin) and clitoral hood are mucous membranes; the urethra is also a mucous membrane. The secreted mucus traps the pathogens in the body, preventing any further activities of diseases.