Figure 19.

Thickness and composition of the alveolar septal wall interstitium. The total thickness of the alveolar septal wall in adult mammals scales with body size (and alveolar curvature, not shown), although the slope of the relationship is relatively shallow. In addition, the relative contributions of collagen and elastin in the septal wall interstitium also increase with body size and scale with alveolar curvature. “Other” includes cellular elements, basement membrane and other non-collagen/non-elastin areas within the interstitial compartment. Note that these data were calculated for the whole width of the alveolar septum, thus the measures of interstitial thickness shown here are 2-fold higher that measured as the arithmetic mean interstitial thickness (see Table 3). From Mercer et al., with permission (191).