Lecture 4 – Respiration III

It will drop when the outer wall moves muscles

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It will drop when the outer wall moves (muscles contract) When the volume of the thoracic cavity expands When the intercostals contract and the ribcage rotates outward and upward, the volume  of the thoracic cavity increases This means hat the volume of intrapleural fluid increases  Consequently, the difference between alveolar pressure and intrapleural pressure will  get steeper Gradient gets more negative Forces the lung to expand Chest Wall Transmural pressure P(intrapleural)-Patm When the lung expands the intrapleural pressure gets sub-atmospheric Increases the transpulmonary pressure Lungs expand Alveolar pressure then drops and becomes sub atmospheric Air will flow in At the end of a normal unforced expiration, there is no air flow Atmospheric pressure is 0, alveolar pressure is 0, intrapleural pressure is about -4 Both are going in towards the intrapleural pressure Lung elastic gradient is balancing the transmural pressure from inside Chest wall elastic recoil is balancing the pressure gradient from the outside
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reticular network and surface tension from surfactant are what are causing the recoil At inspiration The diaphragm starts down Pressure gradient across chest wall becomes steeper The pressure gradient from the alveolar to intrapleural pressure gets steeper Alveolar pressure falls because the lung is expanding Lung is expanding because the intrapleural pressure is becoming more and more  negative, overpowering resting elastic recoil Alveolar pace is becoming stretched and since volume is increasing pressure has to go  down Alveolar pressure goes down below the atmospheric pressure
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Air flows into the lungs Transmural pressure across chest wall changes intrapleural pressure which changes  alveolar pressure
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23:23
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23:23
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