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Extrapulmonary and intrapulmonary bronchus


  1. Principal (primary) bronchus
    Trachea bifurcates at Carina at lower border ofT4 vertebra into right and left principal (primary) bronchi. Right principal bronchus is wider, shorter (2.5 cm long), and more vertical in the line of trachea (250 with median plane). Therefore a foreign body is most likely to lodge in the right bronchus. Right bronchus divides into eparterial and hyparterial bronchi, passing respectively above and below the pulmonary artery, before entering the hilum.
    Left principal bronchus is narrower, longer (5 cm long) and more horizontal (45° with median plane). Left bronchus crosses in front oftheesophagus producing a slight constriction. Inside the lung it divides into 2 lobar bronchi: upper and lower.
  2. Secondary (lobar) bronchus
    Right lung has three lobar bronchi. Eparterial bronchus continues as upper lobar (secondary) bronchus (supplying right upper lobe). Hyparterial bronchus gives off middle lobar (secondary) bronchus (supplying right middle lobe) and then continues as lower lobar (secondary) bronchus (supplying right lower lobe). Thus, eparterial bronchus supplies upper lobe of right lung and hyparterial bronchus supplies middle and lower lobes.
    Right lower lobar (secondary) bronchus is most vertical, nearly continues in the direction of trachea.
    On Left side there are two lobar bronchi upper and lower, supplying upper lobe and lower lobe of left lung respectively.
  3. Tertiary or segmental bronchi
    Lobar or secondary bronchi divides into tertiary bronchi. The part of lung tissue aerated by a tertiary bronchus is called as bronchopulmonary segment which is the anatomical, functional and surgical unit of lung. There are 10 bronchopulmonary segments in each lung, thus each lung has 10 tertiary bronchi. Each tertiary bronchus undergoes about 13 more divisions and ends as lobular bronchiole.

Anatomy of lungs

  1. Lungs are pyramidal or conical shaped organs. Right lung is shorter, wider and heavier (625 gm.) than left lung (565 gm.). Each lung has :- (i) An apex, (ii)A base, (iii) Three borders (anterior, posterior and inferior), and (iv) two surfaces (costal and medial).
  2. Apex lies in the inlet of thorax, 2.5 cm above the clavicle. It is related anteriorly to subclavian artery and vein. Posteriorly it is separated from neck of first rib by (from medial to lateral) sympathetic trunk, fist posterior intercostal vein, superior intercostal artery, and ascending branch of ventral ramus of 1st thoracic nerve.
  3. Base is concave and rests on the diaphragm, which separates the right lung from the right lobe of liver, and the left lung from left lobe of liver, the fundus of stomach and spleen.
  4. The anterior border is thin and is shorter than posterior border. Anterior border on left side shows a wide cardiac notch below the level of 4th costal cartilage. Posterior border is thick and ill defined. It extends from C7 to T10; Inferior border separates the base from the costal and medial surface. Surface marking of inferior surface of lung is 2 levels above the reflection of inferior surface of pleura, i.e. 6th rib in mid clavicular line, 8th rib in midaxillaryline,and 10thrib at lateral border of erector spinae.
  5. Costal surface is large and convex. Medial surface is divided into a posterior (or vertebral) surface and an anterior (or mediastinal) surface. The vertebral surface is related to vertebrae, intervertebral disc, posterior intercostal vessels and splanchnic nerves. Mediastinal surface is related to various structures (differ on right and left side).
    1. Right side:-Right atrium and auricle, right ventricle (partly), SVC, right brachiocephalic vein, azygos vein, esophagus, trachea, right vagus, and right phrenic nerve.
    2. Left side :-Left ventricle, left auricle, infundibulum, right ventricle (partly), pulmonary trunk, arch of aorta, descending thoracic aorta, thoracic duct, left subclavian artery, esophagus, left brachiocephalic vein, left vagus and phrenic nerves, and left recurrent laryngeal nerve.

Fissure and lobes of lungs

The right lung is divided into 3 lobes (upper, middle and lower) by two fissures, oblique and horizontal. The left lung is divided into two lobes (upper and lower) by the oblique fissures. Each lobe is further subdivided into bronchopulmonarysegments. Each lung has 10th bronchopulmonarysegments.


Right lung

Upper lobe

Middle lobe

Lower lobe

1. Apical

2. Posterior

3. Anterior


4. Lateral

5. Medial


6. Superior

7. Anterior basal

8. Medial basal

9. Lateral basal

10. Posterior basal


Left lung

Upper lobe

Lower lobe

1. Apical

2. Posterior    Upper division   Upper division

3. Anterior

4. Superior lingular

5. Inferior lingular   Lower division       

6. Superior
7. Anterior basal
8. Medial basal (absent)

9. Lateral Basal

10.Posterior basal


Azygos lobe

These are accessory lobes and are of three types:-

  1. Upper azygos(above hilum),
  2. Lower azygos(below hilum), and
  3. Lobe of azygos vein (medial part of split apex of right lung).

Features of bronchopulmonary segments

Characteristic features of each bronchopulmonary segment are:-

  • Is a pyramidal shaped segment of lung, with its apex facing the lung root and its base at the pleural surface.
  • Is the largest subdivision of a lobe.
  • Is an independent respiratory unit.
  • Is separated from adjacent segments by connective tissue septa which forms intersegmental planes.
  • Is surrounded by connective tissue which is continuous on the surface with pulmonary pleura.
  • Is supplied independently by a segmental (tertiary) bronchus and a tertiary branch of the pulmonary artery.
  • Is named according to the segmental bronchus supplying.
  • Is drained by intersegmental parts of the pulmonary veins that lie in intersegmental space and drain adjacent segments. Thus each segment has more than one vein and each vein drains more than one segment.
  • Is not a bronchovascular segment, because it does not have its own vein.
  • Is surgically resectable: During removal, the surgeon works along the pulmonary vein to isolate a particular segment.


  1. Apical segment of right lower lobe is the commonest site of aspiration lung abscess and aspiration pneumonia, posterior segment of right upper lobe being the next to get involved. Thus most dependentportionoflung is apical segment of right lowerand posterior segment of right upper lobe.
  2. Posterior segment of the right upper lobe is the most frequent site of tuberculosis.
  3. Anterior segment of upper lobe is the most frequent site of cancer.
  4. Superior segment of lower lobe is related to posterior parts of 4thto 8thribs and can be examined in the triangle of auscultation.

Root (hilum) of the lung

  1. Hilum (root) of the lung connects the medial surface of the lung to the mediastinum. It comprises structures entering or coming out of the lung at the hilum. It lies opposite the T5 to T7 vertebrae. Arrangement of structures in the hilum is as follows -
    1. Anterior to posterior (same on both side) :- (i) Superior pulmonary vein, (ii) Pulmonary artery, (iii) Bronchus
    2. Superior to inferior-
      • Right:- (i) Eparterial bronchus (superior most), (ii) Pulmonary artery, (iii) Hyparterial bronchus, (iv) Inferior pulmonary vein (inferior most).
      • Left: - (i) Pulmonary artery (superior most)(ii) Bronchus, (iii) Inferior pulmonary vein (inferior most).
  2. On right side, hilum of the lung is arched by azygousveinand on left side by arch of aorta.

Relations of the hilum (root)





Common on both sides

-       Phrenic nerve

-       Pericardiophrenic vessels

-       Anterior pulmonary plexus

On right side

-       SVC

-       Part of right atrium

Common on both sides

-       Vagus nerve

-       Posterior pulmonary plexus

On left side

-       Descending thoracic aorta

On right side

Terminal part of azygousvein


On left side

Arch of aorta

Pulmonary ligament


Arterial supply of lung

  1. Bronchial arteries
    1. Right bronchial artery - (1 in number) - is a branch of the 3rdposterior intercostal artery or upper left bronchial artery.
    2. Left bronchial arteries - (2 in number) - are branches of the descending thoracic aorta: the upper one arises opposite T5 and the lower one just below the left bronchus.
    3. Bronchial arteries supply the lung till the beginning of respiratory bronchiole (conducting part) and then anastomose with pulmonary arteries.
  2. Pulmonary arteries
    1. They carry deoxygenated blood from the right side of the heart to the alveoli for oxygenation.
    2. Supply respiratory part of the bronchial tree via pulmonary capillary plexus.

Venous Drainage of Lung

  1. Bronchial veins
    1. Superficial bronchial veins drain pleura and extrapulmonary bronchi. On the right side they drain into the azygos vein and on the left side they drain into the left superior intercostal vein or hemiazygous vein.
    2. Deep bronchial veins drain rest of the bronchial tree and the lung parenchyma and end in pulmonary veins.
  2. Pulmonary veins - (4 in number) - Open into the left atrium of the heart.

Structures related to mediastinal surface of lungs

Only on left side

Only on right side

Common on both sides

  • Left ventricle
  • Left auricle &infundibulum
  • Arch of aorta
  • Descending thoracic aorta
  • Pulmonary trunk
  • Subclavian artery (left)
  • Thoracic duct
  • Recurrent laryngeal nerve(left)
  • Right atrium &auricle
  • Superior venacava
  • Inferior venacava
  • Azygous vein (Arch)
  • Brachiocephalic vein
  • Trachea
  • Esophagus
  • Phrenic nerve
  • Vagus nerve
  • Brachiocephalic vein


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