the walls of the alveoli are mostly made of marble.
the walls of the alveoli are mostly made of marble.
the walls of the alveoli are mostly made of?
marble
Na
Na
the surface tension of a watery surface (the water-air interface) tends to make that surface shrink. when that surface is curved as it is in the alveoli of the lungs, the shrinkage of the surface decreases the diameter of the alveoli. the more acute the curvature of the water-air interface the greater the tendency for the alveolus to collapse. this has three effects. firstly the surface tension inside the alveoli resists expansion of the alveoli during inhalation (i.e. it makes the lung stiff, or non-compliant). surfactant reduces the surface tension and therefore makes the lungs more compliant, or less stiff, than if it were not there. secondly, the diameters of the alveoli increase and decrease during the breathing cycle. this means that the alveoli have a greater tendency to collapse (i.e. cause atelectasis) at the end of exhalation that at the end of inhalation. since surfactant floats on the watery surface, its molecules are more tightly packed together when the alveoli shrink during exhalation. this causes them to have a greater surface tension-lowering effect when the alveoli are small than when they are large (as at the end of inhalation, when the surfactant molecules are more widely spaced). the tendency for the alveoli to collapse is therefore almost the same at the end of exhalation as at the end of inhalation. thirdly, the surface tension of the curved watery layer lining the alveoli tends to draw water from the lung tissues into the alveoli. surfactant reduces this danger to negligible levels, and keeps the alveoli dry.
respiratory system