The trachea connects the upper airways to the lungs. It is essentially a stiff tube (such as a vacuum cleaner tube), which runs in front of the esophagus, for a distance of about 10-15 cm before splitting into the left and right main bronchus (plural: bronchi).
Crucial for the function of the trachea are the rings of cartilage, shaped like a series of horseshoes, that keeps the airways open at all times. These are required or else the trachea would collapse and that would increase the resistance to breathing.
Note the presence of the glands and the hairs sticking out from the mucosa. (See link to paragraph D).
As a side note, the esophagus does not have such horseshoe rings. Therefore, normally, the esophagus is collapsed.
But because of its flexibility, it can easily be distended when a bolus of food is propelled through it.
So; why is it not good for the trachea to be collapsed, like the esophagus? (increased resistance to the airflow)
Back to the trachea. At the carina, the trachea splits into the two main bronchi. These two main bronchi then split further into many more bronchi, like the branches of a tree. (Hence the name ‘bronchial tree’!)
Finally, the last branches (= bronchioli) are reached, which are terminated by blind sacs = the alveoli (singular: alveolus). See next page.
As we said before, the epithelium of the airways (nose, mouth, pharynx, larynx, trachea and bronchi) plays several crucial roles:
a. Moisturizes the air
b. Filters the air
The large particles are trapped in a slimy layer of mucus, which is secreted by the mucosa.
This mucous is created by the glands located in the mucosa all along the whole length of the respiratory pathway; from the nose all the way to the most distal bronchiole.
Their function is extremely important; to filter and clean the air that is inspired. However, what happens to all the filthy particles when they are caught in this mucous?
This is the task of the hairs (=cilia) that is sticking out into the lumen. They beat the mucous down (or up, depending on the location) towards the esophagus where the mucous is then swallowed and digested in the stomach.
Sometimes, especially when we have a cold, our body produces too much mucous which we then either sneeze out or blow it out into our handkerchief.
Interestingly, smoking paralyses the beating of the cilia. This will lead to accumulation of slime in the airways.
(Not very healthy is it?)
That is why smokers always have to cough so much to get rid of their mucus!
This is such an important and potentially life-saving intervention that I have dedicated a special paragraph to it.
Sometimes, accidentally, people swallow something that gets stuck in their throat. This is immediately noticeable, as one will try to cough the object as vigorously as possible out of their pharynx/larynx. This is very often successful.
But sometimes, it is not possible to cough the food out such as when it is wedged to firmly in the throat or when it is too big. If this problem is not solved immediately, such a person will die in a few minutes due to lack of air!
The Heimlich maneuver consists of a second person
1) Standing behind the victim
2) Turn his two hands into a big fist
3) Place the first on the belly, just below the ribs of the patient and
4) Push the fists forcefully in- and upward.
The point of this maneuver is to push the air from the lungs back into the trachea and thereby unplug the plug from the larynx back into the mouth and out to the outside world.
There are some excellent websites that demonstrate clearly how to perform this maneuver (Google: Heimlich maneuver).
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2 / 7
The trachea + lungs:
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A cross-section of the Trachea:
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The Bronchial Tree:
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Transport of Mucous through the Respiratory System: