265 General discussion and future perspectives Table 1. Relation between morphologic structures and representation in microscopy (2-dimensional cross section). With unaltered morphology the measurements in microscopy are proportional with the third dimensional measurements, while with altered morphology such as in the lung the surface measurements are disproportional321. 3- dimensional structure 2-dimensional cross section Stereological relation in vivo Unit Unit Other organ*) Lung#) Alveolar volume μm3 Air surface μm2 Proportional Disprop. Alveolar wall surface μm2 Alveolar line / perimeter μm Proportional Proportional Blood vessel volume μm3 Luminal surface μm2 Proportional Disprop. Blood vessel wall (surface) μm2 Inner (endothelial)/ outer (adventitial) perimeter μm Proportional Proportional Basement membrane surface μm2 Basement membrane line μm Proportional Proportional Elastin fiber μm Elastin fragments (dot) Proportional Proportional *) Organs or disease states where the morphology is not altered during the sampling procedure. Here the value of the measured characteristics in the two-dimensional microscopy are proportional to the values in the third dimension. #) In the periphery of the lung the structure of the underlying morphology is drastically altered during surgery. The amount of air in alveoli and blood and lymph fluid is reduced during iatrogenic collapse. Moreover, the smaller volume requires a smaller surface. Therefore, a relative excess of surface will lead to adaptation. The alveolar basement membrane surface lined with epithelial cells will not reduce during the few minutes of iatrogenic collapse. This will lead to folding of the alveolar wall. The surface measurements in microscopy are not proportional to the volume of the in vivo situation, while the measurements of lines will remain proportional to surface in the third dimension. Disprop. = disproportional 17
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