Overview
The term respiratory tract is an umbrella term for all organs involved in respiration. Within the respiratory tract, a further functional distinction is made between organs that are responsible for conducting the air (so-called air-conducting organs) and those that are ultimately responsible for actual breathing itself (so-called gas exchange, in which the blood is supplied with fresh oxygen and the oxygen consumed in the body is exhaled in the form of carbon dioxide). Another type of classification can be made according to the location of the various organs. A distinction is made here between the upper and lower airways. Besides breathing, the respiratory tract is also involved in the formation of the voice.
Structure
According to the functional classification, there are the sections of the respiratory tract that are responsible for conducting the air to the sections of the respiratory tract where the actual breathing takes place. Air-conducting organs are the nasal cavity, the larynx, the trachea and the bronchi with their branches. The actual respiratory organs, on the other hand, are the smaller end branches of the bronchi in which the actual breathing, namely the gas exchange, takes place (so-called bronchioli respiratorii and the alveoli).
The division of the respiratory tract into the upper and lower respiratory tract is determined by its location. If they lie above the larynx, they belong to the upper airways; if they lie below, they belong to the lower airways. The respiratory tract begins at the nasal cavity.
A distinction is made between a left and right nasal cavity, which are separated from each other by the nasal septum (septum nasi) in the middle (medial). The nasal cavity also houses the human olfactory organ. The connections to the paranasal sinuses are located in the lateral (lateral) nasal walls.
This is where infectious diseases of the nose can find their way into the paranasal sinuses, where they can lead to an unpleasant inflammation of the paranasal sinuses, which can be accompanied by purulent discharge from the nose, difficulties in nasal breathing and a feeling of pressure in the head. There is an opening in the nasal cavity to the back, so that a connection (the choanas) to the pharynx is created and the air can be passed on. The function of the nasal cavity during breathing is also to heat the inhaled air to a temperature that differs from the body temperature by about 1 degree Celsius.
Apart from this, the air is already roughly cleaned of any dirt particles by the hair in the nasal cavity. The oral cavity also belongs to the respiratory tract in terms of its location, because air can also be inhaled through the oral cavity. The next station of the respiratory tract is the pharynx, which is connected to the nasal cavity.
The pharynx is divided into three sections. An upper section, the so-called nasopharynx, which represents the connection to the nasal cavity, a middle section with connection to the oral cavity (oropharynx) and a lower section, the laryngopharynx, which represents the connection to the trachea and esophagus. It is therefore both an airway and an oesophagus, and its function is to convey inhaled air from the nasal cavity to the trachea and to convey food from the oral cavity to the oesophagus.
The larynx is connected to the throat at its lower end. The larynx consists of muscles and cartilage. It separates the windpipe from the oesophagus and ensures that food that is eaten actually gets into the oesophagus and not accidentally into the windpipe, where it could block the airways.
If this happens anyway, there is a risk of not being able to breathe and choking on swallowed food. The next section of the respiratory tract is the windpipe (trachea). It is part of the air conducting system and is the connection to the bronchi of the lungs.
It is about 10-12 cm long, lies in front of (ventrally) the esophagus (oesophagus) towards the stomach and can best be described as an elastic tube, which is connected below the larynx. The trachea is stabilised by horseshoe-shaped cartilage clips, which ensure that the trachea (windpipe) does not collapse due to the negative pressure created during inhalation. The trachea is covered on the inside with a surface that produces a thin film of mucus, which ensures that small particles of dust and dirt that are transported with the inhaled air get caught and can be carried upwards by the cough reflex.
In addition, there are cells on the surface which serve as sensors for the substances contained in the air. The trachea branches out at the level of the 4th/5th thoracic vertebra into the left and right main bronchi, the bronchi principales. The next section of the respiratory tract is the bronchial system.
It is an umbrella term for the airways running through the lungs. The bronchial system can be understood as an ever widening system of tubes that end in the so-called alveoli, where the actual gas exchange takes place. A distinction is also made here between an air-conducting part, which carries the air to the alveoli, and the part responsible for the gas exchange.
The bronchial system begins with the two main bronchi. The right main bronchus branches off the trachea at a slightly steeper angle and supplies the right lung. The left main bronchus accordingly breathes into the left lung.
The slightly steeper angle on the right side ensures that inhaled foreign bodies reach mainly the right main bronchus. Since the heart is located on the left side of the upper body, the left lung is slightly smaller than the right. This is the reason why there are only 2 branches from the left main bronchus, the so-called lobe bronchi (bronchi lobares), while 3 branches from the right main bronchus.
These branches branch off to the segmental bronchi (Bronchi segmentales), analogous to the organization of the lung into segments. For the sake of clarity, these are marked with numbers. There are 10 segmental bronchi on the right and 9 on the left.
This numbering is universal. This means that the numbering of the bronchi is the same for every person, so that it is easier to describe which bronchus is meant, e.g. to explain where a tumour or foreign body is located. The next smaller branch is called lobular bronchus (Bronchus lobularis).
With each further branching, the diameter of the bronchus continues to decrease. This is followed by the so-called bronchioli. These represent the first section of the bronchial tree that no longer contains cartilage.
The diameter of this section is already very small at 1 millimeter. At the end of the bronchioli, they branch out into 4-5 terminal bronchioli, which represent the end of the air-conducting section of the respiratory tract. Now follows the part of the lung responsible for gas exchange.
This is followed by the so-called alveolar ducts (Ducti alveolares), through which the inhaled air enters the alveolar sacs (Sacculi alveolares), which are formed by several alveoli. This is the terminus of the respiratory tract. Gas exchange now takes place in the alveoli, in which fresh oxygen is transferred to the blood and used oxygen is released in the form of CO2 so that it can be exhaled.
