A mucous membrane (plural - mucosae or mucosas; singular - mucosa; Latin: tunica mucosa) is a lining of mostly endodermal origin. It consists of an epithelium (a layer, or layers of epithelial cells) and an underlying lamina propria of connective tissue. Mucosae line various cavities of the body that are either externally exposed to the environment or are internal organs, and the mucous membranes ensure that the underlying lamina propria of connective tissue remains moist. They are at several places contiguous with skin: at the nostrils, the lips of the mouth, the eyelids, the ears, the trachea, the stomach, the genital area, and the anus.
Mucus prevents pathogens and dirt from entering the body and prevents bodily tissue from losing moisture. Mucous membranes are rather delicate; they are able to absorb a number of substances and toxins but are vulnerable regarding pain. If the lining is torn or broken, mucus is incapable of performing its roles of preventing infection and retaining tissue moisture levels.
In the female, the glans clitoridis and the clitoral hood have mucous membranes. In the male, the glans penis (the head of the penis) and the inner layer of the foreskin have mucous membranes. The urethra is also lined with a mucous membrane. Some mucous membranes are involved with digestion in the absorption of insoluble food molecules and secretion (releasing chemicals from glands). The thick fluid secreted by some mucous membranes and/or associated glands is termed mucus. The mucus can be protective.