Bronchial tubes
The bronchial tree consists of bronchi as well as bronchioles and leads to the alveoli (air sacs). The bronchial tree represents the air conduction system of the body. The bronchi are the airways running in the lungs.
Antomy
The bronchial tree is located below the trachea and represents the airways in the lungs. The trachea divides at the level of the fourth and fifth thoracic vertebrae into the two main bronchi (bronchi principales). Due to the structure of the lung into two lobes, a distinction is made between the right and left bronchial tree. The trunk of each bronchial tree is the main bronchus and divides further into a widely branched system of tubes. In the process, the diameter of the bronchi becomes smaller and smaller and is only less than 1 mm in the bronchioles. In the process, the wall of the bronchi also becomes thinner and thinner and changes structurally. The bronchial tree represents the air conduction system of the lung, in that no gas exchange takes place.
Different types of bronchi
The main bronchus divides into three lobe bronchi in the right lung. On the left lung side, the main bronchus branches into only two lobe bronchi. After this branching, the lobe bronchi each divide further into segmental bronchi. After this, further branching takes place:
Bronchi lobares >> Bronchi segmentales >> Bronchioli (Bronchiolen) >> Bronchioli terminales >> Bronchioli respiratorii
Bronchi lobares (lobe bronchi):
- one per lobe of lung (three in right lung; two in left lung).
Bronchi segmentales (segmental bronchi):
- one per lung segment (ten in the right lung; nine in the left lung).
- A lung segment is a defined section of the lung supplied by a segmental bronchus as well as a segmental artery.
- Segmental bronchi divide further into bronchioles.
Air-conducting bronchioles/bronchioles
- have no cartilage structure
Bronchioli terminales (terminal bronchi).
- smallest, thinnest air-conducting sections of the bronchial tree
- transition to the respiratory bronchioles
Bronchioli respiratori (respiratory bronchioles).
- first section of the lower respiratory tract in which gas exchange takes place
- end in the alveoli
Wall structure
The bronchi are first surrounded by cartilaginous braces. These serve to stabilize the bronchi. The shape of the cartilage braces have a horseshoe-like shape. In this case, the ends of the cartilage are connected by smooth muscles. The proportion of cartilage in the bronchioles decreases significantly during branching and that of the musculature increases. There is then no cartilage left in the bronchioles. They now consist only of smooth muscle.
The wall of the bronchi basically consists of three layers. The tunica mucosa contains the respiratory epithelium (ciliated epithelium/lamina epithelialis). Dirt and mucus are transported through this towards the pharynx. Furthermore, the respiratory air is warmed up through this layer due to the high blood circulation. The tunica mucosa contains elastic fibers that serve to adapt to the variable thoracic volume. Furthermore, this wall layer is involved in immune defense and forms mucus through seromucous glands contained in the lamina propria.
The second layer is the tunica fibromusculocartilaginea andt contains the hyaline cartilage brace. This causes the change in the diameter of the bronchi, which serves to control the distribution of air. Even in case of negative intrathoracic pressure, the tunica fibromusculocartilaginae keeps the lumen open.
The tunica adventitia serves for vegetative regulation and supply. Vessels, nerves and connective tissue are preserved in this layer.
Division of the bronchial tree
The bronchi each supply one lung segment. This can also be seen in the names of the bronchi and the lung segments.
| Bronchus principalis dexter | Bronchus principalis sinister | ||
| Bronchus lobaris superior dexter: | Bronchus lobaris superior sinister: | ||
| Bronchus segmentalis apicalis (I) | Bronchus segmentalis apicoposterior (I+II) | ||
| Bronchus segmentalis posterior(II) | |||
| Bronchus segmentalis anterior (III) | Bronchus segmentalis anterior (III) | ||
| Bronchus lobaris medius dexter: | |||
| Bronchus segmentalis lateralis (IV) | Bronchus lingularis superior (IV) | ||
| Bronchus segmentalis medialis (V) | Bronchus lingularis inferior (V) | ||
| Bronchus lobaris inferior dexter: | Bronchus lobaris inferior sinister: | ||
| Bronchus segmentalis superior (VI) | Bronchus segmentalis superior (VI) | ||
| Bronchus segmentalis basalis medialis (VII) | Bronchus segmentalis basalis medialis (VII) | ||
| Bronchus segemtalis basalis medialis (VIII) | Bronchus segmentalis basalis anterior (VIII) | ||
| Bronchus segmentalis basalis lateralis (IX) | Bronchus segmentalis basalis lateralis (IX) | ||
| Bronchus segmentalis basalis posterior (X) | Bronchus segmentalis basalis posterior (X) |
Function
The bronchial tree directs the respiratory air from the upper airways or trachea to the alveoli, which are located at the end of the bronchioles. The airflow is created due to the movement of the chest and diaphragm.The alveoli are surrounded by tiny blood vessels where gas exchange takes place. There, oxygen passes through the thin walls into the blood. Carbon dioxide is also released from the blood into the air. The air with the carbon in it is then exhaled.
Inside the bronchi is the epithelium, which serves to produce mucus. It also transports small particles that have entered the bronchial system through the breathing air out of the bronchi. The smallest particles transported into the throat are then coughed up.
During physical activity, for example sports, the bronchial tubes change. The muscles of the bronchi are activated by the sympathetic nervous system. This leads to a relaxation of the muscles around the bronchi. This increases the diameter of the bronchi and allows more air to pass through them to the alveoli. As a result, the blood can be supplied with more oxygen.
During periods of physical rest, on the other hand, the bronchi decay. This occurs due to the activation of the parasympathetic nervous system.
Development
The anlagen for the main bronchi develop from the lung buds during the embryonic phase. The main bronchi divide once on the left and twice on the right. Thus, the pulmonary bronchi develop corresponding to the five lobes of the lungs.
In der darauffolgenden pseudoglanduläre Phase bildet sich der Bronchialbaum bis hin zu den Bronchioli terminales. In dieser Zeit werden aber noch keine Alveolen oder Bronchi respiratorii entwickelt. Das Innere der Bronchien und Bronchiolen wird mit dem Vorläufer des späteren Flimmerepithels, ein hochprismatisches Epithel, ausgestattet.
Subsequently, in the canalicular phase, the lumen of the bronchi expands and the bronchioli respiratorii and alveolar ducts are formed. Furthermore, the sprouting of capillaries takes place now, so the basis for the gas exchange is formed.
In the following two phases, saccular and alveolar phase, mainly the alveoli are further developed.
Diseases
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