Stereology of the lung.

Many scientific projects require a quantitative assessment of organ, tissue and cell (ultra)structure. Such quantitative (morphometric) data are essential to make statistically valid comparisons between experimental groups. The structures of interest are measured at different microscopic levels. However, measurements in microscopy pose two problems: 1) Only a small fraction of the whole biological system can be analyzed (sampling problem). 2) The analysis is performed on nearly two-dimensional (physical, optical or virtual) sections through the object although the aim is to obtain biologically meaningful three-dimensional data (3D vs 2D problem). These problems are solved by the application of unbiased sampling and measurement tools known as stereology. This chapter gives a brief introduction to the theory and practical application of stereology, using the lung as an example. Stereological tools needed to quantify volume, number and surface area are introduced and examples are given how to estimate total lung volume, volume of lung parenchyma, alveolar surface area and number of alveolar epithelial type II cells per lung.