Mucosa

Related articles: gastric mucosa; intestinal mucosa

The mucosa - also called mucous membrane or mucous membrane - is a layered structure that covers the internal surface of the organism's cavities and canals communicating with the outside. Among the numerous examples of hollow organs that communicate with the external environment we mention those of the digestive, urogenital, auditory and respiratory systems.

The function of the mucous membranes is to coat and protect the underlying surfaces, while carrying out secretory and / or absorption activities.

The nature of the cells that make up the mucous membranes reflects their specialization, which always and in any case has to do with the interaction between the external and internal environment (gas exchange, excretion, absorption, digestion, secretion, etc.).

In the image on the side, for example, we can appreciate how in the intestinal mucosa the epithelium is everted, forming structures called intestinal villi, covered by absorbent epithelial cells; these cells, in turn, have a surface structure called brush border, consisting of numerous expansions, the microvilli, which perform the important function of increasing the absorbent surface of the epithelium.

If we take the respiratory mucosa, however, we notice the presence of a pseudostratified (sometimes multilayered) ciliated and mucosecerning epithelium covering. The presence of mucus, together with the action of the eyelashes, facilitates the trapping of microorganisms, dust and foreign particles, favoring at the same time their elimination towards the outside.

The mucous membranes consist of three overlapping laminae, of varying thickness depending on the body areas examined. These layers are called epithelium (epithelial lamina), basement membrane and lamina propria. Some mucous membranes, such as those of the digestive system, have a fourth lamina - the muscolaris mucosa - consisting of a thin layer of smooth muscle fibers, which separates them from the underlying tunic.

The surface lamina is made up of epithelial covering tissue (plain or multi-layered paving, etc. depending on the features considered and their function). The basal lamina consists of a continuous muco-polysaccharide layer, reinforced by reticular collagen fibers. The lamina propria, on the other hand, contains connective tissue of the fibrillar type with support functions; in its thickness, moreover, glands, lymphoid cells and fine nerve, blood and lymphatic networks can be found.

Most mucous membranes contain glands that secrete mucus. This stringy and viscous substance, more or less dense, protects and lubricates the membranes themselves and is secreted in greater quantities during local inflammatory processes.