![]() ![]() Was more difficult, inhalation would be very, very difficult if not impossible.įortunately, our alveoli do not collapse & inhalation is relativelyĮasy because the lungs produce a substance called surfactant that reduces Would make it more difficult to 're-expand' the alveoli (when you inhaled).īoth of these would represent serious problems: if alveoli collapsed they wouldĬontain no air & no oxygen to diffuse into the blood &, if 're-expansion' Potentially, surface tension could cause alveoli to collapse and, in addition, When we exhale & our alveoli become smaller (like air leaving a balloon). Increases as water molecules come closer together, which is what happens ![]() Water molecules, including those on theĪlveolar walls, are more attracted to each other than to air, and thisĪttraction creates a force called surface tension. The walls of alveoli are coated with a thin film of water & ![]() Lungs (and alveoli) to become slight positive relative to atmospheric pressure.Īs a result, air leaves the lungs (check this animation by McGraw-Hill). As a result,Īir moves from an area of higher pressure (the air) to an area of lower To become slightly negative relative to atmospheric pressure. The expansion of the lungs causes the pressure in the lungs (and alveoli) Intra-alveolar pressure during inspiration & expirationĪs the external intercostals & diaphragm contract, the lungs expand.
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