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

When the lungs decrease in volume, the pressure inside the lungs (alveolar pressure) becomes positive compared to the atmospheric pressure. Due to the positive pressure, the gas inside the lungs flows out. When the lungs remain decreased at a constant volume, the positive pressure disappears and the flow ceases.

When the lungs decrease in volume, due to decrease in the thoracic cavity volume from inspiratory muscle relaxation, the pressure inside the lungs (alveolar pressure) is positive compared to the atmospheric pressure. Note that the yellow pressure gauge is lower on the lung side, compared to the outer-side, which is open and thus indicates the atmospheric pressure. When the lungs remain decreased at a constant volume, the positive pressure disappears and the flow ceases.

As mentioned in a former step, the decrease in lung volume is due to the elasticity of the lungs.
 
lung volume (within one quiet respiratory cycle)maxmax→minmin
pressure inside the lungs (alveolar pressure)atmospheric pressurepositive pressureatmospheric pressure
flownoneoutnone

チャレンジクイズ

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

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

3 When the lungs decrease in volume,

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

4 When the lungs are kept at a decreased volume,

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

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: Lung elasticity

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