Bronchial mucus: what it is and what it is used for

Bronchial mucus is essential to maintain healthy and defend the airways and, therefore, also the lungs from external agents. Here is its composition and all functions.

Research carried out in recent years has made it possible to identify the substances that constitute it, also discovering what they are used for.

Biochemical analysis of human bronchial fluid shows that, under physiological conditions, mucus has the following composition:

Water 95%
Proteins 0,1-0,5%
Lipids 0,3-0,5%
Glycoproteins 3%
Salts approx. 1%

The constituents of mucus can be of secretory origin, in the sense that they are processed by cells or glands of the bronchial wall, or plasma, that is, coming from plasma.

The secretory components of mucus

They consist mainly of mucins (mucoglycoproteins), proteins with a high molecular weight and high carbohydrate content (>80%).

From the chemical point of view they are macromolecules consisting of a central protein axis to which numerous side chains of polysaccharides are linked.

Other secretory components of mucus are represented by secretory immunoglobulins A (IgA), which serve to protect the external mucous surfaces. Then there is lactoferrin, which plays an important role in protecting the bronchial mucosa against germs.

Finally, there are secretory enzymes (transferase, glycosidase and callidinogenodase) and a component of alveolar origin, surfactant

The functions of mucus

The main function of mucus is to keep the airways in optimal condition. And it does so in many ways: first of all it acts as a physical and biological obstacle, forming a mucous film that represents an efficient barrier to the crossing of substances inhaled with breathing.

Then it is essential to ensure the humidification of the air that passes through the trachea and the large bronchi.

Numerous experimental studies have shown that, in the absence of mucus, the respiratory tract changes profoundly, causing, on some occasions, substantial damage to the anatomical structures of the lung.

It is well known, for example, that the absence of mucus in the airways can cause an irritative inflammatory reaction.

It also performs an important filter and dilution task: there are many irritating or toxic gases for the respiratory tract subjected to a filtration and dilution process through the mucous surface of the airways.

It also serves to remove particles, dust and biological agents. Every day a normal individual breathes particles of an extremely different nature such as plant substances (spores and pollen), bacteria and viruses, fumes containing dust derived from the combustion of coal and tobacco, and others.

The quantity and quality of inhaled particles varies greatly depending on the environment in which the individual breathes and many other individual factors.

The diffusion of these particles along the airways depends not only on their dimensional characteristics, but also on the conditions of the surface of the respiratory tract, in particular on the amount of mucus that is found in the airways and that actively participates, through the mechanism of mucociliary clearance, in the purification of the respiratory tract.

Mucociliary clearance

This term refers to the mechanism of rapid purification of trochaeous-bronchial mucus that is realized through the coordinated movement of vibratory cilia and facilitated by mucus secretions.

The mucociliary apparatus is one of the most important means of defense of the respiratory tree because it intercepts and transports outside not only contaminating particles, but the same physiological or pathological secretions, representing a fundamental element for maintaining the integrity of the mucous membrane of the bronchi.

The deposition and elimination of inhaled particles takes place in different ways and times in the different tracts of the respiratory system: for example, there is a significant difference between the anterior nasal region (which does not have ciliated epithelium) and the posterior one (which instead is provided with it).

It has been shown that mucociliary purification occurs more quickly in the posterior one than in the anterior one and this explains, even if only partially, the greater incidence of pathology in the front of the nose compared to the posterior.

Mucus macrophages

In the most peripheral areas of the lung, particle purification is not based on the mechanism of mucociliary “clearance”, but requires the intervention of macrophages which, through phagocytosis, can incorporate foreign substances and remove them from the respiratory surface.

The mechanical purification of the airways depends on the ciliary activity, the driving element of drainage. And bronchial secretions, which represent the indispensable vehicle for the transport and elimination of particles and inhaled pollutants.

It is therefore understood that qualitative and quantitative changes in bronchial secretions are capable of altering mucociliary drainage even if ciliary activity remains functioning.

When mucolytics are needed

Productive cough and phlegm: when these symptoms appear, typical of winter ailments, in addition to the therapeutic intervention that aims to solve the causes (antibiotics) it is therefore necessary to intervene directly on the mucus itself in order to make clearance and, consequently, expectoration easier.

For this purpose, drugs called mucolytics are needed. Some act directly on the mucus, breaking the molecular bonds of the mucoproteins and therefore breaking the polymeric structure of the mucus, others change the characteristics of the mucus by modifying in various ways the adhesiveness, hydration, varying the biochemistry and secretion of mucus.

Among the mucolytics a prominent place belongs to the sobrerol which, from its commercialization (1970) to today, has represented and represents one of the cornerstones of the class of mucoactive drugs for its proven effectiveness and excellent tolerability even in a more delicate age group such as pediatrics.

This molecule, due to its pharmacokinetic characteristics (rapid absorption, mucotropism, rapid elimination through the renal filter), its pharmacological properties (changes in the rheological characteristics of mucus, fluidification of sputum, increased mucociliary clearance) and its safety supported by about 30 years of extensive clinical use (no serious adverse reactions have occurred in clinical trials, to date), occupies a place of great importance in the treatment of hypersecretory pathology of the upper and lower respiratory tract.

Joycelyn Elders is the author and creator of EmpowerEssence, a health and wellness blog. Elders is a respected public health advocate and pediatrician dedicated to promoting general health and well-being.

The blog covers a wide range of topics related to health and wellness, with articles organized into several categories.

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