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• Structure: the trachea is a rigid fibroelastic structure. Incom-
The respiratory tract is most often discussed in terms of upper and
plete rings of hyaline cartilage continuously maintain the patency of
lower parts. The upper respiratory tract relates to the nasopharynx and
larynx whereas the lower relates to the trachea, bronchi and lungs.
the lumen. The trachea is lined internally with ciliated columnar
epithelium.
The pleurae • Relations: behind the trachea lies the oesophagus. The 2nd, 3rd and
• Each pleura consists of two layers: a visceral layer which is adherent 4th tracheal rings are crossed anteriorly by the thyroid isthmus (Figs 5.3
to the lung and a parietal layer which lines the inner aspect of the chest and 64.1).
wall, diaphragm and sides of the pericardium and mediastinum. • Blood supply: the trachea receives its blood supply from branches of
• At the hilum of the lung the visceral and parietal layers become con- the inferior thyroid and bronchial arteries.
tinuous. This cuff hangs loosely over the hilum and is known as the pul-
monary ligament. It permits expansion of the pulmonary veins and The bronchi and bronchopulmonary segments (Fig. 5.2)
movement of hilar structures during respiration (Fig. 5.1). • The right main bronchus is shorter, wider and takes a more vertical
• The two pleural cavities do not connect. course than the left. The width and vertical course of the right main
• The pleural cavity contains a small amount of pleural fluid which acts bronchus account for the tendency for inhaled foreign bodies to prefer-
as a lubricant decreasing friction between the pleurae. entially impact in the right middle and lower lobe bronchi.
• During maximal inspiration the lungs almost fill the pleural cavities. • The left main bronchus enters the hilum and divides into a superior
In quiet inspiration the lungs do not expand fully into the costo- and inferior lobar bronchus. The right main bronchus gives off the
diaphragmatic and costomediastinal recesses of the pleural cavity. bronchus to the upper lobe prior to entering the hilum and once into the
• The parietal pleura is sensitive to pain and touch (carried by the inter- hilum divides into middle and inferior lobar bronchi.
costal and phrenic nerves). The visceral pleura is sensitive only to • Each lobar bronchus divides within the lobe into segmental bronchi.
stretch (carried by autonomic afferents from the pulmonary plexus). Each segmental bronchus enters a bronchopulmonary segment.
Air can enter the pleural cavity following a fractured rib or a torn • Each bronchopulmonary segment is pyramidal in shape with its apex
lung (pneumothorax). This eliminates the normal negative pleural directed towards the hilum (see Fig. 6.1). It is a structural unit of a lobe
pressure, causing the lung to collapse. that has its own segmental bronchus, artery and lymphatics. If one
Inflammation of the pleura (pleurisy) results from infection of the bronchopulmonary segment is diseased it may be resected with pre-
adjacent lung (pneumonia). When this occurs the inflammatory process servation of the rest of the lobe. The veins draining each segment are
renders the pleura sticky. Under these circumstances a pleural rub can intersegmental.
often be auscultated over the affected region during inspiration and Bronchial carcinoma is the commonest cancer among men in the
expiration. Pus in the pleural cavity (secondary to an infective process) United Kingdom. Four main histological types occur of which small
is termed an empyema. cell carries the worst prognosis. The overall prognosis remains
appalling with only 10% of sufferers surviving 5 years. It occurs most
The trachea (Fig. 5.2) commonly in the mucous membranes lining the major bronchi near the
• Course: the trachea commences at the level of the cricoid cartilage in hilum. Local invasion and spread to hilar and tracheobronchial nodes
the neck (C6). It terminates at the level of the angle of Louis (T4/5) occurs early.
where it bifurcates into right and left main bronchi.

The pleura and airways 15