3.8.3: Lung volume, pressure inside the lungs and air flow-1

When the lungs increase in volume, the pressure inside the lungs (alveolar pressure) becomes negative compared to the atmospheric pressure. Due to the negative pressure, gas (air) flows into the lungs. When the lungs remain increased at a constant volume, the negative pressure disappears and the flow ceases.

The yellow pressure gauge indicates the pressure inside the lungs. The pressure inside the lungs is also called alveolar pressure, to specify anatomic location. When the lungs increase in volume, due to increase in the thoracic cavity volume from inspiratory muscle contraction, the pressure inside the lungs (alveolar pressure) is negative compared to the atmospheric pressure. Note that the yellow pressure gauge, with its tip inside the lung, is elevated on the lung side, compared to the outer-side, which is open and thus indicates the atmospheric pressure. When the lungs remain increased at a constant volume, the negative pressure disappears and the flow ceases.
 
lung volume (within one quiet respiratory cycle)minmin→maxmax
pressure inside the lungs (alveolar pressure)atmospheric pressurenegative pressureatmospheric pressure
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チャレンジクイズ

1 When the lungs increase in volume, the pressure inside the lungs (alveolar pressure) is negative compared equal positive compared  to the atmospheric pressure.

2 When the lungs are kept at an increased volume, the pressure inside the lungs (alveolar pressure) is equal negative compared positive compared  to the atmospheric pressure.

3 When the lungs are increasing in volume,

gas flows out
gas (air) flows in
there is no gas flow
.

4 When the lungs are kept at an increased volume,

gas (air) flows in
there is no gas flow
gas flows out
.

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: Lung volume, pressure inside the lungs and air flow-2

: Diaphragm activity and lung volume -2