ABSTRACT
The lung is a complex heterogeneous tissue adapted for gaseous exchange. As shown in the schematic in Figure 12.1, the lung comprises a lobular structure with each lobe having its own blood supply originating from the bronchial arteries. The lungs are contained within the thoracic cavity and are surrounded by the parietal and visceral pleural membranes. The latter membrane is directly adherent to
the lung surface tissue, while the parietal pleura lines the chest wall. The two pleurae are lubricated by serous fluid and the region between them – intrapleural space – has a subatmospheric pressure. When the muscles of the diaphragm and the intercostal muscles of the ribcage contract there is an increase in intrathoracic volume. Correspondingly, during quiet breathing the intrapleural pressure (at the start of inspiration approximately −2.5 mm Hg relative to atmospheric) decreases to approximately −6 mm Hg and the lungs expand, and the pressure in the airways becomes slightly negative and air flows into the lungs – ‘inspiration’.
