The richly branched bronchi divert the air from the trachea to the alveoli. Read more about their function and possible diseases here!


The bronchia are part of the lung system that serves as a breathing system. After dividing the trachea into a right and a left main bronchus (one branch for the two lungs), made numerous other branches, which fill the entire lung and finally into the alveoli, where the gas exchange between breathing air and Blood takes place. Read all about the bronchi!

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  • What are the bronchi?

  • What is the function of the bronchi?

  • Where are the bronchi?

  • What problems can the bronchi cause?

What are the bronchi?

The bronchi form a richly branched tube system in the lungs - a guidance system for the breathing air: The two main bronchi emerge from the division of the trachea and lead into one of the two lungs. There are still numerous other branches, the bronchi becoming smaller and thinner: First, each main bronchus divides into three (right lung) and two (left lung) lobe bronchi - corresponding to the three or two lung lobes. That the left lung has a lobe less than the right is because the heart needs space.

The lobar bronchi branch further into the segment bronchi, which also continue to ramify. The smallest bronchi, whose diameter is less than one millimeter, are called bronchioles. They lead to the tiny, delicate alveoli, in which the gas exchange takes place.

With increasing branching of the bronchi, their wall structure changes: first, the walls are reinforced by cartilage clasps to keep them stable. The free ends of these cartilage braces are strained by strands of smooth muscle controlled by the nervous system. In the course of the branching, the cartilage portion in the walls decreases, while the proportion of smooth muscle increases. Finally, the bronchioles only have one muscle wall without cartilage.

What is the function of the bronchi?

The bronchi conduct the air from the upper respiratory tract (nose, mouth, pharynx, larynx) and trachea to the approximately 300 million alveoli at the end of the bronchioles. These are surrounded by a network of tiny blood vessels (capillaries) and the place for the gas exchange: Through the gossamer walls of the alveoli, oxygen from the breathing air is released into the blood and carbon dioxide is absorbed from the blood into the respiratory air, which is then exhaled.

The interior of the bronchi (like that of the trachea and the upper respiratory tract) is lined by a respiratory epithelium. It contains, among other things, cells that produce mucus, where small and very small particles that have entered with the breath are stuck. Adjacent ciliated epithelial cells then carry these particles with their cilia to the outside, where they can be coughed off.

In physically active phases, for example during sports or during hard physical work, the activation of the sympathetic nervous system relaxes the muscles around the bronchi. These have a larger diameter and it can flow through more air and reach the alveoli: The blood is supplied with more oxygen. During periods of physical rest, the bronchi narrow because the parasympathetic nervous system is then activated.

What can you do about the painful cough? And how can we prevent it?

Where are the bronchi?

The bronchi are located inside the lung in the thorax. The main bronchi begin at the end of the trachea at the level of the fourth thoracic vertebrae.

What problems can the bronchi cause?

The most common bronchial health problem is acute inflammation (bronchitis). It is usually caused by viruses and usually heals without complications, but can also become chronic. If virus-induced bronchitis causes additional colonization of the mucous membrane by bacteria, treatment with antibiotics is necessary.

In people with bronchial asthma, allergens (allergy triggers) or irritants (such as cold air or smoke) cause the bronchi to contract convulsively, causing paroxysmal breathing (asthma attack). Worldwide, around 100 million people suffer from asthma, experts estimate.

Also, a chronic constriction and inflammation of the bronchi is possible (especially in long-term smokers). Then one speaks of chronic obstructive bronchitis. In addition, if the alveoli are partially destroyed and overstretched (pulmonary emphysema), there is a chronic obstructive pulmonary disease (COPD).

Smoking can also cause the formation of a malignant tumor bronchia trigger. This bronchial carcinoma (lung cancer) is the most common cause of death in men and the third most common cause of cancer death in women.

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