During the aging process, the lung exhibits structural changes accompanied by a decline in its function. The related information currently available is still scarce and contradictory. In addition, changes in some pulmonary parameters through aging process are species- and strain-dependent. The aim of this study was the assessment of the area and the number of pulmonary alveoli through the normal aging process in CD1 mouse. Paraffin-embedded sections of lungs from CD1 mice at age of 2, 6, 12, 18, or 24 months were stained with hematoxylin and eosin and examined using a light microscope. Images were captured using a camera linked to an image analysis software to measure areas and count alveoli. There was a significant difference in the alveolar area among the ages analyzed (F=87.53, Sig.=0.000). The alveolar area of the 6-, 12-, 18-, and 24-month-old mice was significantly greater (all p values < 0.001) than in mice at 2 months of age. Also, the alveolar number was significantly different among the ages tested (F=3.21, Sig.=0.023). The number of alveoli in mice at 2 months of age was greater than in mice at all other age groups, reaching statistical significance when compared with the 6-, 12-, and 18-month-old mice (p values of 0.044, 0.014, and 0.002, respectively). Thus, we observed an increase in alveolar area and a decrease in alveolar number through the aging process. This information might be useful to understand pathologic changes underlying susceptibility of elderly individuals to chronic lower respiratory tract diseases.

<b><i>Introduction:</i></b> The diameter and area of the proximal convoluted tubule (PCT) and the distal convoluted tubule (DCT) are of the main parameters analyzed in stereological studies of the kidney. However, there is no consensus about if the PCT and DCT should be considered circular or elliptical in shape. <b><i>Objective:</i></b> To analyze if there are significant differences in the diameter and area of the PCT and DCT, depending on whether they are considered circular or elliptical. <b><i>Methods:</i></b> Paraffin-embedded sections of kidneys from CD1 mice were stained with hematoxylin and eosin and examined using a light microscope. Images were captured using a camera linked to image analysis software. A short diameter (<i>d</i>) and a long diameter (<i>D</i>) were measured in both PCT and DCT. A small circular area (SCA), a large circular area (LCA), and an elliptical area (EA) were calculated with mathematical formulas that incorporate <i>d</i> and <i>D</i> values, while a program area (PA) was provided by the software. <b><i>Results:</i></b> There was a significant difference between <i>d</i> and <i>D</i> in both PCT (<i>F</i> = 1.354, Sig = 0.000) and DCT (<i>F</i> = 4.989, Sig = 0.000). Also, there were significant differences in the tubular areas in both PCT (<i>F</i> = 34.843, Sig = 0.000) and DCT (<i>F</i> = 22.390, Sig = 0.000); circular areas were different from elliptical areas (SCA and LCA vs. EA and PA). <b><i>Conclusion:</i></b> The convoluted tubules of the nephron must not be considered circular, but rather elliptical; care should be taken every time the tubules are analyzed in stereological studies of the kidney, especially when evaluating their diameters and areas.