RLO: Ventilation

School of Nursing and Academic Division of Midwifery

Inhalation (at rest)

Inhalation takes place when the diaphragm and the external intercostal muscles contract to enlarge the chest cavity. The bell-shape of the diaphragm flattens and pulls-down to a lower position in the thorax, while the external intercostal muscles swing the ribs and sternum up and outwards, like the handle of a bucket lifting.

As we have seen earlier, the parietal pleura that lines the chest wall forms a sealed, fluid-filled space with the visceral pleura that covers the lung surface. When the parietal pleura moves outwards with the chest wall during inhalation, it pulls a vacuum in the pleural cavity which creates a drop in intrapleural pressure. As a result of this, the visceral pleura is “sucked” outwards bringing the walls of the lungs with it and causing the lungs to increase in volume. This draws air into the lungs from the atmosphere.