Bronchopulmonary Segments of the Lung

Prepared and reviewed by the PrepElephant Academic Review Team

First published 2 Oct 2026 · Spot an error?

On this page

Direct answer
What you must remember
Applying segments at the bedside and in theatre
Where the examiner expects precision
Frequently asked questions
Related topics

Direct answer

A bronchopulmonary segment is the smallest functionally independent unit of lung: a pyramid with its apex at the hilum and base on the pleural surface, served by its own segmental bronchus and pulmonary artery branch, with veins running intersegmentally between segments. The right lung has ten segments (three upper, two middle, five lower) and the left has nine or, by some accounts, eight to nine — an apicoposterior and anterior pair, two lingular segments, and four to five lower lobe segments — the fusion reflecting the left lung's accommodation of the heart. Each segment can be individually resected, individually diseased and individually drained by postural positioning, which is what makes the anatomy worth memorising.

What you must remember

Right upper lobe (B1-B3): apical, posterior, anterior; right middle lobe (B4-B5): medial and lateral; right lower lobe (B6-B10): superior (apical basal), medial basal, anterior basal, lateral basal, posterior basal.
Left lung fusion: apical and posterior merge as the apicoposterior segment, and the medial and anterior basal segments commonly fuse as anteromedial basal — hence nine (often counted as eight to nine) segments.
Lingular distinction: the left upper lobe's lingula (superior and inferior segments) is the homologue of the right middle lobe, not a separate lobe.
Intersegmental veins: pulmonary veins run between segments and mark the bloodless plane for segmentectomy, exactly as hepatic veins define liver segments.
Atelectasis shapes: each segment collapses in a characteristic pattern — anterior segment shadows along the cardiac border, medial basal behind the heart where it is easily missed on a frontal film.
Postural drainage logic: upper lobe apical segments drain upright; anterior segments supine; posterior basal segments drain best prone with the foot of the bed raised — the physiotherapist applies this daily in bronchiectasis.
Disease tropism: apical and posterior segments of the upper lobes are the favourite sites for post-primary tuberculosis reactivation because of higher oxygen tension and slower lymph flow — a point Indian examiners expect in any TB-rich setting.

Applying segments at the bedside and in theatre

Consider a patient with bronchiectasis producing copious sputum. The high-resolution CT shows bilateral basal disease worst in the posterior basal segments. The physiotherapy prescription is anatomy made practical: the posterior basal segment of each lower lobe drains posteromedially and upward only when the patient lies prone in a head-down position, so that is how the bed is arranged. Change the involved segment to the right middle lobe and the position changes entirely — supine, head down, rotated left, because the segment's bronchus points upward and backward from its origin.

Now move to theatre. A solitary carcinoid in the right upper lobe posterior segment is removed by segmentectomy: the surgeon isolates the posterior segmental bronchus and artery at the hilum, divides them, and then follows the intersegmental vein, which guides the parenchymal plane. Preserve that vein and the adjacent segments keep their drainage. The same reasoning governs tuberculosis surgery in India's thoracic practice — apicoposterior resections for destroyed apical disease with massive haemoptysis — and explains why a radiologist reporting "segmental collapse of the medial basal segment" is telling the surgeon the lesion hides behind the cardiac silhouette on the frontal view and needs a lateral film.

Where the examiner expects precision

Two questions decide most vivas. First, why does the left lung have fewer segments — the answer must invoke fusion (apicoposterior, anteromedial basal) due to the cardiac notch and left-sided position of the heart, not "absence" of tissue. Second, the internal architecture — the segmental bronchus and artery are central, the vein intersegmental — and the surgical corollary that the intersegmental plane is the avascular plane. Examiners then probe applied anatomy: which segments drain in the head-down prone position (posterior basal), which segment is most commonly involved in aspiration in the supine patient (superior segment of the lower lobe, because its bronchus opens posteriorly and dependently), and which segments host reactivation tuberculosis (apical and posterior of upper lobes). Each answer converts a memorised list into clinical behaviour, which is precisely the standard the viva rewards.

Frequently asked questions

How many bronchopulmonary segments does each lung have?

The right lung has ten and the left lung nine (counted variously as eight to nine), the difference explained by fusion into apicoposterior and anteromedial basal segments.

Why are intersegmental veins important in segmentectomy?

They run in the planes between segments and mark the relatively avascular boundary along which the surgeon separates parenchyma while preserving drainage of adjacent segments.

Which segment is most often involved when a supine patient aspirates?

The superior segment of the lower lobe, because its bronchus arises posteriorly and points dependently in the lying position.

Which segments show reactivation tuberculosis preferentially?

The apical and posterior segments of the upper lobes, attributed to higher oxygen tension and less effective lymphatic clearance in the erect lung.

What is the lingula and to what does it correspond?

The anteroinferior tongue of the left upper lobe with superior and inferior segments, the homologue of the right middle lobe.