Bernhard Wolfgang, Haslam Patricia L, Floros Joanna
Department of Neonatology, Faculty of Medicine, Eberhard-Karls-University, Calwer Strasse 7, D-72076 Tübingen, Germany.
Am J Respir Cell Mol Biol. 2004 Jan;30(1):6-11. doi: 10.1165/rcmb.2003-0158TR.
Pulmonary surfactant is a surface-active mixture of phospholipids and specific proteins that lines the epithelial surfaces of mammalian lungs. In the alveoli, its main function is to reduce surface tension to ensure that these structures can remain open during respiratory cycles of contraction and expansion. However, surfactant is also present in the conducting airways, even though they are relatively rigid and do not need a system capable of rapidly lowering surface tension in response to compression. This has raised the question whether there is a difference in composition and function between airway and alveolar surfactant. Interest in this question has been stimulated further by the recognition that surfactant also has important functions in the immune defenses of the respiratory tract. In this review, we describe differences that have been reported between human airway and alveolar surfactant. In addition, we draw parallels between human airway surfactant and surfactant from the lungs of birds. The latter are tubular and rigid and do not undergo cycles of contraction and expansion, thus more resembling the human conducting airways than alveoli. Using this as a model, we propose a new hypothesis to explain structural and functional differences between human airway and alveolar surfactant. We suggest that the molecular composition of surfactant is adapted to differences in the architecture of pulmonary surfaces and to the dynamics of surface area changes during respiration.
肺表面活性物质是一种由磷脂和特定蛋白质组成的表面活性混合物，覆盖在哺乳动物肺的上皮表面。在肺泡中，其主要功能是降低表面张力，以确保这些结构在呼吸周期的收缩和扩张过程中能够保持开放。然而，表面活性物质也存在于传导气道中，尽管它们相对坚硬，并不需要一个能够响应压缩而迅速降低表面张力的系统。这就引发了一个问题，即气道表面活性物质和肺泡表面活性物质在组成和功能上是否存在差异。认识到表面活性物质在呼吸道免疫防御中也具有重要功能，进一步激发了人们对这个问题的兴趣。在这篇综述中，我们描述了已报道的人类气道表面活性物质和肺泡表面活性物质之间的差异。此外，我们还将人类气道表面活性物质与鸟类肺表面活性物质进行了比较。鸟类的肺是管状且坚硬的，不会经历收缩和扩张周期，因此与人类的传导气道更为相似，而不是肺泡。以此为模型，我们提出了一个新的假说来解释人类气道表面活性物质和肺泡表面活性物质之间的结构和功能差异。我们认为，表面活性物质的分子组成适应了肺表面结构的差异以及呼吸过程中表面积变化的动态过程。
