The function of the membrane is to stop pathogens and dirt from entering the body and to prevent bodily tissues from becoming dehydrated.

The mucosa is composed of one or more layers of epithelial cells that secrete mucus, and an underlying lamina propria of loose connective tissue.

[2][3] Mucous membranes line the digestive, respiratory and reproductive tracts and are the primary barrier between the external world and the interior of the body; in an adult human the total surface area of the mucosa is about 400 square meters while the surface area of the skin is about 2 square meters.

[4]: 1  Along with providing a physical barrier, they also contain key parts of the immune system and serve as the interface between the body proper and the microbiome.

[5] Exceptions include the palate, cheeks, floor of the mouth, gums, lips and the portion of the anal canal below the pectinate line, which are all ectodermal in origin.