Hilfer S R
Scan Electron Microsc. 1983(Pt 3):1387-401.
Development of the lungs in mammals begins with the formation of pharyngeal buds that undergo repeated branching to establish the bronchial tree. Late in fetal life the most superficial buds begin to form side branches that will develop into the respiratory surfaces of the lung; the alveolar ducts, alveolar sacs, and alveoli. The bronchial ciliated cells and Clara cells first appear on the seventeenth day of gestation in the mouse. In the respiratory region, a few lamellar bodies are found by 16 days but identifiable type II pneumocytes and extracellular surfactant are not found until 18 days. Flattened type I pneumocytes do not form until after birth, on day 19 or 20. The epithelial branches of the lung are surrounded by mesenchyme and covered by a capsule. At 16 days, the branches are separated by a compact mesenchyme that is highly cellular. By 18 days, the mesenchymal space begins to be reduced. By 19 days, the air passages expand and the mesenchyme forms a thin layer between branches. Little experimental work has been done on the role of the mesenchyme in differentiation of the respiratory surfaces. Since branching of the embryonic lung is influenced by the kind of mesenchyme surrounding the epithelium at early stages, it is likely that mesenchymal control is exerted at later stages in the fetus.
哺乳动物肺部的发育始于咽芽的形成，咽芽会反复分支以建立支气管树。在胎儿期晚期，最表层的芽开始形成侧支，这些侧支将发育成肺的呼吸表面，即肺泡管、肺泡囊和肺泡。支气管纤毛细胞和克拉拉细胞最早在小鼠妊娠第17天出现。在呼吸区域，16天时可发现一些板层小体，但直到18天才发现可识别的II型肺细胞和细胞外表面活性剂。扁平的I型肺细胞直到出生后第19天或20天才形成。肺的上皮分支被间充质包围并被一层包膜覆盖。16天时，分支被高度细胞化的致密间充质分隔开。到18天时，间充质空间开始减小。到19天时，气道扩张，间充质在分支之间形成一层薄层。关于间充质在呼吸表面分化中的作用，几乎没有进行过实验研究。由于胚胎期肺的分支在早期受到上皮周围间充质类型的影响，因此间充质很可能在胎儿后期发挥控制作用。
