Human respiratory tract from beginning to end
Any beginning is amazing. But as for the respiratory tract, the first step is to find out where, in fact, they begin. If you say that in the mouth, you will not be alone in this opinion-so many answer, but this is a mistake. Although we often use the mouth for breathing, kissing, or Smoking, it is still anatomically related to the digestive tract and is microscopically closer to the intestines than to the bronchi: its main function is to eat, not to breathe.
The airway begins with the nose, which shares many functional and anatomical features with the bronchi. The Creator decided that we should breathe mainly through the nose, not through the mouth. And he had good reasons for this, which we will discuss in detail in the section “what is the connection between the nose and lungs?“. Thus, we have sorted out the beginning. What’s next? Let’s follow the movement of the oxygen molecule through the respiratory tract — from beginning to end.
So, the nose is the initial part of the upper respiratory tract, from here our molecule goes on a journey. It passes into the nostrils, the vestibule of the nose and the bumpy surface of the three nasal conchs, and then enters the back of the nasal cavity-the nasopharynx.
Here it is important not to lose orientation, because the nasopharynx crosses the digestive tract and respiratory tract, and in controversial cases, it is the breath that has the advantage! An unusual formation acts as a traffic controller — a soft palate tongue hanging down. At this point, nature finally separates the paths for food and air. The esophagus, which consists of muscles and mucosa, leads to the stomach. It is located at the back of the neck, adjacent directly to the spine. The larynx and the Airways leading from it are located in front of the esophagus. As a result, each time you swallow, the airway is tightly blocked by the epiglottis attached to the back of the tongue. This means that when we swallow, we cannot breathe (naturally, and speak), and Vice versa. An attempt to do both at the same time is interrupted by nature with a fit of coughing or, in the worst case, suffocation. So at the table we must be silent! This is not a consequence of the asceticism that Protestantism has fostered in people for centuries, but biological expediency in full accordance with the laws of Darwinism: the one who eats and keeps quiet survives!
If our air molecule were unlucky, it might end up in the digestive tract at this point and lose the most interesting part of the journey. But, fortunately, the molecule turns in the right direction and through the paired vocal cords, which also belong to the larynx, enters the trachea.
This is where the lower respiratory tract begins, and this is the longest part of our journey, passing through the bronchi. The bronchi also have their beginning (trachea) and at least 400 million endings — pulmonary vesicles, or alveoli. This is where our journey ends.
What explains such an unimaginably large number of alveoli? On the way to them, the Airways constantly branch out and become thinner and more tender. There are 23 branches in total, and each time our molecule must decide whether to turn right or left. From the motorway, it goes first to ordinary multi-lane roads, then to single-lane, country roads, and finally to paths. The last of them after the 23rd fork ends in a dead end-the alveolus. Isn’t it amazing that on this journey, the molecule is given a choice of 400 million Parking spaces?
However, the alveola is not strictly speaking a Parking lot, you can’t sit here for a long time. It is more like a toll booth before the molecule enters the bloodstream — the ultimate destination of its journey, here and only here, in the pulmonary vesicles, is the gas exchange between oxygen and carbon dioxide.
The trachea and bronchi (up to about the 16th branch) serve only as pipelines that direct air to the plexus of the alveoli. Only there does the oxygen molecule overcome the thin barrier between the respiratory and circulatory systems and collide with a carbon dioxide molecule moving towards it, after which it joins the red blood cell. With the flow of blood, it gets to the heart, which, continuously Contracting, sends blood to the most remote parts of the body. Insatiable producers and consumers of energy, such as muscles or the brain, are waiting for oxygen there.
The end of the respiratory tract — the vast universe of the alveoli-is the place where the boundary between the external world of the environment and the internal world of the body is mysteriously blurred. This transition point is very fragile and vulnerable in all living and breathing creatures: reptiles, fish, mammals. Here the air becomes flesh, and the flesh becomes air, and it is this process that sustains life. But the greatest danger lies in the direct influence of the external world. The transition process is vulnerable, but not defenseless!