A bronchopulmonary segment is a unit of lung tissue that functions as an independent respiratory and structural region. It is shaped like a pyramid, with the narrow apex pointing toward the lung root (hilum) and the wide base facing the outer surface of the lung. Each segment operates largely on its own, separated from its neighbors by thin walls of connective tissue. Understanding these segments is fundamental to diagnosing and treating lung diseases.
Anatomical Division of the Lungs
The lungs are organized into lobes, which are further divided into named bronchopulmonary segments. This organization follows the bronchial tree, where main bronchi branch into lobar (secondary) bronchi, which then divide into segmental (tertiary) bronchi. Each segmental bronchus supplies a single segment, creating an efficient system of air distribution.
The right lung has three lobes and typically contains ten segments: three in the upper lobe, two in the middle lobe, and five in the lower lobe. These segments are named according to their position, such as apical, posterior, or medial basal. The left lung has two lobes and usually contains eight to ten segments, often fewer due to the fusion of some segments, such as the apical and posterior combining into an apicoposterior segment. The boundaries between segments are thin layers of connective tissue, which influences the spread of disease and surgical planning.
The Functional Independence of Each Segment
The functional independence of the bronchopulmonary segment stems from its unique vascular and airway supply. Air is supplied by a single, dedicated segmental bronchus, and deoxygenated blood by its own branch of the pulmonary artery; both travel centrally into the segment.
This central positioning contrasts sharply with the pulmonary veins, which carry oxygenated blood out. The veins are located in the connective tissue planes between the segments, known as the intersegmental septa. This intersegmental location is the basis for the segment’s functional autonomy.
Since the veins run along the edges and drain multiple adjacent segments, they effectively outline the segment’s borders. This anatomical arrangement means that if a single segment is diseased, its localized air and arterial supply can be isolated and removed without disturbing the venous drainage or blood flow of the healthy, neighboring segments.
Clinical Importance in Disease and Surgery
Understanding bronchopulmonary segments is important for diagnosis and surgical planning. In localized infections, such as pneumonia or tuberculosis, the connective tissue boundaries often contain the disease within a single segment. This compartmentalization allows clinicians to use imaging techniques like CT scans to precisely localize the pathology.
Pinpointing a lesion’s exact location is necessary for treating lung cancer and other masses. For small tumors, surgeons can perform a segmentectomy, which is the surgical removal of only the diseased segment. This targeted approach preserves the maximum amount of healthy lung tissue, offering a significant advantage over removing an entire lobe (lobectomy).
This precise surgical technique is guided by the intersegmental veins, which serve as landmarks for separating the segments. Preserving functional lung tissue through segmentectomy benefits the patient’s post-operative breathing function. This anatomical knowledge allows for specific interventions that minimize the impact on respiratory capacity and improve recovery.