Physical Aspects of the Human Body by Hartmut Zabel

Author:Hartmut Zabel
Language: eng
Format: epub
Publisher: De Gruyter
Published: 2022-10-26T18:22:51.302000+00:00

Fig. 9.7: Volume change of the thoracic cavity during respiration (reproduced from OpenStax Anatomy and Physiology, © Creative Commons).

Fig. 9.8: Pressures and pressure differences at rest and during inspiration and expiration, demonstrated with a simple mechanical model.  = barometric pressure,  = gas pressure in the alveoli,  = pressure in the pleural cavity. are the respective pressure differences.

During inspiration, the thorax expands due to the action of the intercostal muscles and due to the diaphragm pulling downwards. This pull increases the thoracic cage volume. As the lungs adhere to the thoracic wall, the lung volume will also expand. Furthermore, the elastic forces between lungs and thorax increase slightly the intrapleural space such that the pleural pressure difference drops from 500 to 750 Pa with respect to the barometric pressure. As the pleural pressure decreases and the lungs expand, so do the alveoli inside the lungs. This expansion causes a pressure drop in the alveoli with respect to the environment to about = 150 Pa. The transmural pressure difference increases to about +600 Pa during inspiration. Because of this inspiratory pressure drop in the alveolar space and increased volume, air will flow into the lungs until the pressure difference is balanced.

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