Mucosa

The mucosa - also known as the mucous membrane or mucous membrane - is a layered structure that covers the inner surface of the cavities and the channels of the body communicating with the outside. Among the numerous examples of hollow organs that communicate with the external environment we recall those of the digestive, urogenital, auditory and respiratory systems.

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

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

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

If we take the respiratory mucosa, instead, we note the presence of a pseudostratified epithelium of coating (sometimes multilayered) ciliate and mucosecreting. The presence of mucus, together with the action of the eyelashes, facilitates the trapping of microorganisms, dust and foreign particles, at the same time favoring 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 tract, possess a fourth lamina - the muscularis mucosa - consisting of a thin layer of smooth muscle fibers, which separates them from the underlying cassock.

The surface lamina is constituted by epithelial covering fabric (simple or multi-layered pavement etc. according to the features considered and their function). The basal lamina consists of a continuous muco-polysaccharide layer, reinforced by collagen reticular fibers. The lamina propria, on the other hand, contains fibrillar connective tissue with supporting functions; in its thickness, moreover, glands, lymphoid cells and fine nerve, blood and lymphatic nets can be found.

Most mucous membranes contain mucus-secreting glands. 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.