The mucosa, also known as the mucous membrane, is a soft, moist and pink layer of cells that lines several passages and cavities of the body with openings exposed to the external environment. It is commonly found in the body's digestive, respiratory, reproductive and urinary tracts. The term "mucosa" is the singular form of the mucous membrane; more than one mucosa requires the use of the term "mucosae" instead.
The mucous membrane is so named because it secretes mucus. This is a slimy, slippery substance that acts as the membrane's protective secretion. A major constituent of mucus is the glycoprotein mucin, which is produced by specialized epithelial cells called goblet cells in the mucous membrane. It is this component that is responsible for the texture of mucus, since it is notably responsible for forming jelly-like material.
Mucosa—or rather, the mucus it secretes—is most often associated with the nostrils of the nose. The membrane, however, can be found in several other places in the body. This includes the anus, genitalia, ears, eyelids, mouth and lips.
The main purpose of mucosa is to provide the area where it is located with lubrication. This lessens the restriction of substances or materials going from one place to another in the body. It also acts as a protective shield against harmful agents by trapping them to halt their intended activities.
The nasal mucosa, which provides the mucous lining of the nostrils among other parts of the nasal cavity, is probably the best known type of this membrane. It prevents agents such as dust, bacteria, allergens and pollutants from entering the respiratory system. The nasal mucosa also includes the olfactory mucosa, which can be found in the upper nasal cavity and contains the necessary nerve endings for the sense of smell.
The intestinal mucosa is another notable type of the mucous membrane. It lines the innermost layer of the body's intestines and is really a combination of three types of tissue: the epithelium, lamina propria and muscularis mucosae. When humans eat food, the intestinal mucous membrane come in direct contact with it, and it is largely responsible for breaking the food down into parts that are small enough for absorption. It also plays a role in the secretion of mucus, among other substances.
Some mucosa have specialized names. For instance, the endometrium is the medical term of the mucous membrane lining the mammalian uterus. The glans clitoridis, which is the external portion of the clitoris, and the glans penis, which is the head of the penis, are also considered mucosae.