Lung segments are clearly defined sections of the lung, each supplied by its own small bronchus and its own artery. They form the functional subunits of each lung and play an important role in understanding how the lungs are structured.
The structure of the lungs – more than just a right and left side
The human lungs consist of two main parts, the right lung and the left lung. But the division does not stop there. Each lung is further divided into sections called lobes. The right lung has three lobes and the left has two. These lobes can then be divided into smaller units called lung segments.
In total, there are typically ten segments per lung. In the right lung they are spread across three lobes, and in the left usually across two, although the exact number and arrangement can vary slightly. Each segment has its own airway and blood supply. This means that if one segment stops working properly, for example because of an infection, the rest of the lungs can still carry on.
Why are lung segments medically important?
The division into lung segments is important for medical professionals for several reasons. During an operation, for example to remove a tumour, only the affected segment can be removed precisely, without losing an entire lobe. Knowledge of the segments also helps with diagnosis: doctors can look at X-rays or CT scans and say exactly which area a change is in. This makes treatment easier and often less invasive.
In addition, infections or other lung conditions do not always spread evenly. They sometimes affect only individual segments. If a medical letter mentions an "infiltration in segment 6 on the right", this refers to a very specific area of the right lung. This makes it possible to record exactly where a pneumonia, a tumour, or another change is located.
How are the segments named?
Each lung segment has its own number and a name that relates to its position. The numbering starts at the top of the lung and runs downwards. For example, there is the apical segment (top), the anterior segment (front), and the basal segment (bottom). In reports, descriptions such as "segment 1 left" or "segment 7 right" will appear.
The names are there to make communication between doctors easier. Precise descriptions are especially important when planning operations or when reviewing scans, in order to avoid misunderstandings.
What does this mean for reports and medical letters?
If a medical report mentions a specific lung segment, it is simply describing the location of a finding or a procedure. For example, it might say: "round lesion in segment 3 left" or "atelectasis in segment 9 right". This means that the change in question is located in exactly that section of the lung.
For treatment or prognosis, what usually matters more is how large the change is and how it affects lung function. The segment reference is mainly there to help the treating specialists act precisely and plan further treatment.
When is knowledge of lung segments relevant?
In everyday life, the division of the lungs into segments does not matter much to most people. However, it becomes important whenever there are illnesses, operations, or imaging examinations involved. During a bronchoscopy, which is a procedure that looks inside the airways, specialists also use the segments as a guide to take samples or assess changes.
Overall, lung segments help to better understand the complex structure of the lungs and to carry out medical procedures more precisely. Anyone who reads a reference to a specific segment in a report can take it to mean one thing: it is an exact location within the lungs.
