Anatomy

The combined weight of both lungs is approximately 850 g in the male, 750 g in the female. The apex of each lung is situated in the root of the neck, the base of the lung on the diaphragm. The mediastinum is medial to the lungs and ribs are present laterally. The hilum of each lung contains a main bronchus, pulmonary artery, two pulmonary veins, pulmonary nerve plexus and lymph nodes.

The lungs are separated into lobes by invaginations of pleura along fissures (Figure 38.1). The right lung is divided into three lobes by the oblique and horizontal fissures, the left into two lobes by the oblique fissure. The inferior part of the left upper lobe (the lingula) is the homologue of the right middle lobe.

The trachea branches at the level of T4 and T5 into two main bronchi. The right bronchus enters the lung behind the right pulmonary artery, the left bronchus crosses behind the left pulmonary artery and enters the lung below it. The main bronchi divide to give five lobar bronchi. These then divide into segmental bronchi supplying the 19 bronchopulmonary segments. Segments are roughly wedge shaped with their base at the pleural surface. Each segment is supplied by a segmental artery and bronchus. Veins draining segments often anastomose with

Trachea

Trachea

Figure 38.1. Anatomy of the lungs. 1. Main bronchus. 2. Upper lobe. 3. Middle lobe. 4. Lower lobe. Reproduced from Hermanek P, Hutter RVP, Sobin LH, Wagner G, Wittekind Ch (eds.). TNM Atlas: illustrated guide to the TNM/pTNM classification of malignant tumours, 4th edition. Springer-Verlag: Berlin and Heidelberg, 1997.

Figure 38.1. Anatomy of the lungs. 1. Main bronchus. 2. Upper lobe. 3. Middle lobe. 4. Lower lobe. Reproduced from Hermanek P, Hutter RVP, Sobin LH, Wagner G, Wittekind Ch (eds.). TNM Atlas: illustrated guide to the TNM/pTNM classification of malignant tumours, 4th edition. Springer-Verlag: Berlin and Heidelberg, 1997.

those from adjacent segments. Bronchopulmonary segments can be resected with little haemorrhage or leakage of air from adjacent raw surfaces. Further divisions of the bronchi produce bronchioles. Glands and cartilage are present in the walls of bronchi but not in bronchioles.

Bronchioles have a diameter of less than 1 mm. Terminal bronchioles lead to respiratory bronchioles which branch to produce alveolar ducts, alveolar sacs and then alveoli. The lung may be divided into lobules, areas that measure 1-2 cm across and are poorly demarcated by incomplete fibrous septa. Each lobule is made up of three to ten acini. An acinus or terminal respiratory unit is that portion of the lung supplied by one terminal bronchiole. Pulmonary arteries are found at the centres of each acinus alongside bronchioles, whereas pulmonary veins run in the interlobular septa. Flattened type 1 pneumocytes and occasional rounded type 2 pneumocytes line the alveoli.

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