The Physiology Of The Lungs

1053 WordsNov 16, 20165 Pages
Physiology of the Lungs There are several factors that oppose and promote alveolar collapse, including the transmural pressure gradient, pulmonary surfactant, alveolar interdependence (all opposing factors), alveolar surface tension and the elasticity of stretched pulmonary connective tissue fibres (promoting factors). I will discuss these different aspects of lung physiology here. Transmural Pressure Gradient and Elasticity of Stretched Pulmonary Connective Tissue Fibres There are three important pressures involved in respiration. These are the atmospheric, intra-alveolar and intrapleural pressures. The atmospheric pressure sits relatively constant at approximately 760mmHg, and is simply the pressure exerted by the atmospheric air at sea level.1 The intra-alveolar pressure is the pressure within the alveoli, which varies in different stages of the respiratory cycle, but eventually equates with the atmospheric pressure. Upon inspiration, the chest wall expands outwardly and the diaphragm contracts downwards, pulling the lungs with them and so forcing the alveoli open. The pressure within the alveoli falls and air enters the lungs down the pressure gradient. On expiration, the diaphragm relaxes and the chest wall and stretched lungs will recoil to their pre-inspiratory size due to their elastic properties. This recoil causes the intra-alveolar pressure to rise and so air will leave the lungs following the pressure gradient until the intra-alveolar pressure is equal to that of
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