Alcorn D G, Adamson T M, Maloney J E, Robinson P M
Anat Rec. 1981 Dec;201(4):655-67. doi: 10.1002/ar.1092010410.
In the sheep, fetal lung development proceeds to a later stage of maturity than in smaller laboratory animals. Of the four stages in pulmonary development recognizable in this species - embryologic, pseudoglandular, canalicular, and aveolar - the latter three are described in the present study using histologic, morphometric, and ultrastructural techniques. During the pseudoglandular stage, the major airways developed centrifugally. Cartilaginous, glandular, muscular, vascular, and neural elements were present in major airway walls from an early age. During the canalicular stage, volume expansion of the lung was accomplished by rapid growth of large terminal spaces. In the final stage, alveoli were formed following subdivision of the large terminal spaces by alveolar crests. The alveolar lining epithelium differentiated during the latter two stages producing a large increase in alveolar surface area, particularly during the alveolar stage; a large increase in pulmonary capillary surface area also accompanied alveolar development. Thus, just prior to birth, the fetal sheep lung has a well-developed air-way system and alveolar network, in preparation for postnatal gas exchange.
与较小的实验动物相比，绵羊胎儿的肺发育会进入到更成熟的阶段。在该物种肺发育可识别的四个阶段——胚胎期、假腺期、小管期和肺泡期——中，本研究使用组织学、形态计量学和超微结构技术描述了后三个阶段。在假腺期，主要气道呈离心性发育。从早期开始，主要气道壁中就存在软骨、腺体、肌肉、血管和神经成分。在小管期，肺体积的扩大是通过大终末腔隙的快速生长来实现的。在最后阶段，大终末腔隙被肺泡嵴分隔后形成肺泡。肺泡内衬上皮在后面两个阶段发生分化，导致肺泡表面积大幅增加，尤其是在肺泡期；肺毛细血管表面积也随着肺泡发育而大幅增加。因此，在出生前，胎儿绵羊的肺拥有发育良好的气道系统和肺泡网络，为出生后的气体交换做好准备。
