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BIL 118 (28)

alveolar gas exchange

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BIL 118
O' Sullivan

Alveolar Gas Exchange  Greater partial pressure of O2 in alveolar air / more O2 dissolves in blood (Henry's Law)  Alveoli walls are composed of endothelium → gases diffuse through 2 thin cells o Alveoli is constantly moist o O2 can dissolve and diffuse through the cells into the blood o It is then taken up by haemoglobin  Alveoli contain phagocytes to kill bacteria that have not been trapped by mucus  O2 diffuses down its conc. gradient from air to blood; CO2 diffuses from blood to air  Ventilation: Flow of air in and out of alveoli Ventilation  Tidal volume, VT, volume of air inhaled and exhaled in a normal single breath (≈0.5 L)  Functional residual capacity, FRC, volume remaining in lungs after exhalation of tidal volume (≈2.5 L)  Expiratory reserve volume, ER, volume of a maximal exhalation (≈1.5 L)  Residual volume, RV, volume remaining in lung after maximal exhalation (≈1L)  Inspiratory reserve volume, IR, additional volume that can be inhaled after inhalation of tidal volume  Vital capacity, VC, maximum volume of exhalation after lungs are maximally filled o best clinical indicator of breathing  Minute ventilation is the overall flow of air into lungs (analogous to cardiac output) o Minute Ventilation = Tidal Volume x Respiratory Rate o (0.5 litre/breath * 10 breaths/min = 5 litres per minute)  "Dead space" - not all O2 available in air is available to alveoli o Fresh air mixes with exhaled air during inspiration o Alveolar ventilation takes dead space into account o Alveolar ventilation = (Tidal Volume - Dead Space) x Respiratory Rate o (350 ml x 10 breaths per
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