Institute of Anatomy, University of Bern, Bern, Switzerland.
PLoS One. 2021 Nov 8;16(11):e0257349. doi: 10.1371/journal.pone.0257349. eCollection 2021.
Pulmonary acini represent the functional gas-exchanging units of the lung. Due to technical limitations, individual acini cannot be identified on microscopic lung sections. To overcome these limitations, we imaged the right lower lobes of instillation-fixed rat lungs from postnatal days P4, P10, P21, and P60 at the TOMCAT beamline of the Swiss Light Source synchrotron facility at a voxel size of 1.48 μm. Individual acini were segmented from the three-dimensional data by closing the airways at the transition from conducting to gas exchanging airways. For a subset of acini (N = 268), we followed the acinar development by stereologically assessing their volume and their number of alveoli. We found that the mean volume of the acini increases 23 times during the observed time-frame. The coefficients of variation dropped from 1.26 to 0.49 and the difference between the mean volumes of the fraction of the 20% smallest to the 20% largest acini decreased from a factor of 27.26 (day 4) to a factor of 4.07 (day 60), i.e. shows a smaller dispersion at later time points. The acinar volumes show a large variation early in lung development and homogenize during maturation of the lung by reducing their size distribution by a factor of 7 until adulthood. The homogenization of the acinar sizes hints at an optimization of the gas-exchange region in the lungs of adult animals and that acini of different size are not evenly distributed in the lungs. This likely leads to more homogeneous ventilation at later stages in lung development.
肺腺泡是肺的功能气体交换单位。由于技术限制，在显微镜下的肺切片中无法识别单个腺泡。为了克服这些限制，我们在瑞士光源同步加速器设施的 TOMCAT 光束线上，对出生后第 4、10、21 和 60 天的大鼠肺进行了右下叶的灌注固定成像，体素大小为 1.48μm。通过在导气到换气气道的交界处关闭气道，从三维数据中分割出单个腺泡。对于一部分腺泡（N=268），我们通过体视学评估它们的体积和肺泡数量来跟踪腺泡的发育。我们发现，在观察到的时间范围内，腺泡的平均体积增加了 23 倍。变异系数从 1.26 下降到 0.49，并且 20%最小和 20%最大腺泡的平均体积之间的差异从 27.26 倍（第 4 天）减少到 4.07 倍（第 60 天），即随着时间的推移，差异变小。在肺发育早期，腺泡体积变化较大，随着肺的成熟，通过将其体积分布减少 7 倍，使其均匀化。腺泡大小的均匀化表明成年动物肺部的气体交换区域得到了优化，并且不同大小的腺泡在肺部不是均匀分布的。这可能导致肺发育后期通气更加均匀。
