Protective barriers in the lungs
It is not difficult to imagine what would have happened if the smallest particles of dust, aerosols, various microorganisms contained in the air we breathe fell into the lungs. Very soon their delicate and extremely vulnerable tissue would collapse: after all, the wall thickness of the alveoli – microscopic bubbles – ranges from 0.1 to 4 micrometers. However, thanks to the system of protective mechanisms that stand all the way of the air stream from the moment of inspiration up to the alveoli, this does not occur, and the air enters the lungs sufficiently purified from harmful impurities and even warmed up.
The first filter, through which the inhaled air passes, can be seen with the naked eye, looking at itself in the mirror: these are hairs at the beginning of the nasal openings, which retain large dust particles suspended in the air. The details of the next filter, the nasal mucosa, can only be viewed with a microscope. By the way, this picture is surprisingly beautiful: under a raster electron microscope, the mucous membrane looks like a waving field of rye or wheat. Such an impression is created by ciliated epithelium cells, throughout the airways covering the mucous membrane. Each ciliated cell has up to 200 cilia, 3–7 micrometers long, producing 160–250 vibrations per minute. The movements of all cilia are strictly coordinated: they oscillate towards the nasopharynx, constantly pushing nasal mucus, produced by the nasal mucosa, as it were.
On the mucous membrane of the sinuous walls of the nasal cavity up to 40% of various foreign particles contained in the air are deposited, and only relatively large particles of more than 50 micrometers are trapped here, and smaller ones penetrate deeper into the trachea, bronchi, where air purification continues as functions of the ciliary epithelium (cilia of epithelial cells move upward, pushing the secret into the nasopharynx), and due to the presence of. It is produced by mucous glands located in the wall of the trachea and bronchi, as well as the goblet cells of the epithelium covering the mucous membrane of these organs. Antibodies, immunoglobulins, proteins, carbohydrates, lipids, enzymes – this is not a complete list of the components of this secret. But the tracheobronchial secret is first of all due to its antiviral and antibacterial properties, perhaps, to substances such as lysozyme, interferon, lactofirrin and pyrogens.
Lysozyme destroys the cell wall of microbes, making them unviable. This substance is a fairly effective weapon against pathogens, and when its content in the tracheobronchial secretion decreases, favorable conditions are created for the development of infection.
Another important component of the secret – interferon provides nonspecific protection of the respiratory system, It acts primarily on the cells of the body, making them impregnable for pathogens. It is not by chance that interferon preparations are widely used in medical practice as a prophylactic against influenza; effective interferon and in the initial stages of the development of SARS.
Endogenous pyrogens, which are part of the tracheobronchial secretion, cause the development of a protective febrile reaction: an increase in body temperature of 2 to 3 degrees has a detrimental effect on many bacteria and viruses. And what is not less significant, the temperature increase stimulates the production of interferon by the cells of the body. In this regard, I would like to remind once again: do not take immediately, as soon as the temperature has risen, aspirin, amidopyrine and other antipyretic drugs. Let the body’s natural defense factors work in full force!
Together with the ciliated epithelium and the tracheobronchial secret, the phagocytic defense system also stands guard over the purity of air entering the lungs. It turns on when pathogens and viruses, bypassing all previous barriers, reach the alveoli. Here they are waiting for alveolar macrophages and neutrophils – cells-orderlies. They are actively moving and attacking alien microorganisms, absorb and digest them.
In the lungs, there is also an immunological defense system, which, like in other organs, is provided with lymphoid cells. Along the airways in the mucous membranes and submucosa are clusters of lymphoid cells – lymph – epithelial nodules: the small bronchi are especially rich in them. Cells of nodules in response to the invasion of bacteria, viruses produce antibodies that neutralize pathogens. When there are few aggressors, lympho – epithelial nodules cope on their own. With mass infection, the immune organs, regional lymph nodes, are included in the defense reactions. thymus, red bone marrow, spleen.
Finally, the most recent protective barrier is surfactant. Surfactants that form this thinnest film lining the walls of the alveoli, envelop, partially neutralize a variety of foreign particles, microorganisms, which can achieve microscopic bubbles. Part of the spent surfactant is removed from the lungs through the bronchi along with the tracheobronchial secret, while the other part is absorbed and digested by macrophages.
As you can see, nature has provided a fairly powerful set of protective mechanisms, put more than one barrier in the path of inhaled air. But often we ourselves break the work of these mechanisms, open the way to the lungs for infections. After all, if we breathe through our mouths all the time, the inhaled air passes through one of the most important barriers – the nasal cavity mucosa, so it is completely uncleaned and unheated, which enters the trachea and bronchi, which can lead to the development of tracheitis, bronchitis.
And how detrimental are the effects on the protective barriers of substances contained in tobacco smoke! In smokers, the ciliary epithelium partially dies, and the oscillations of the cilia of functioning cells slow down dramatically. Of course, this reduces the speed of movement of the nasal mucus, tracheobronchial secretion. Favorable conditions are created for large numbers of pathogens to accumulate in the airways. viruses, and hence for the development of the infectious process. Moreover, the surfactant under the influence of tobacco smoke loses its protective properties and the ability to clean the alveoli from foreign particles. It is no accident that heavy smokers are so susceptible to viral and bacterial respiratory infections.