Dobbs Leland G, Johnson Meshell D
Department of Medicine, University of California San Francisco, San Francisco, CA 94118, USA.
Respir Physiol Neurobiol. 2007 Dec 15;159(3):283-300. doi: 10.1016/j.resp.2007.06.011. Epub 2007 Jun 29.
The alveolar surface comprises >99% of the internal surface area of the lungs. At birth, the fetal lung rapidly converts from a state of net fluid secretion, which is necessary for normal fetal lung development, to a state in which there is a minimal amount of alveolar liquid. The alveolar surface epithelium facing the air compartment is composed of TI and TII cells. The morphometric characteristics of both cell types are fairly constant over a range of mammalian species varying in body weight by a factor of approximately 50,000. From the conservation of size and shape across species, one may infer that both TI and TII cells also have important conserved functions. The regulation of alveolar ion and liquid transport has been extensively investigated using a variety of experimental models, including whole animal, isolated lung, isolated cell, and cultured cell model systems, each with their inherent strengths and weaknesses. The results obtained with different model systems and a variety of different species point to both interesting parallels and some surprising differences. Sometimes it has been difficult to reconcile results obtained with different model systems. In this section, the primary focus will be on aspects of alveolar ion and liquid transport under normal physiologic conditions, emphasizing newer data and describing evolving paradigms of lung ion and fluid transport. We will highlight some of the unanswered questions, outline the similarities and differences in results obtained with different model systems, and describe some of the complex and interweaving regulatory networks.
肺泡表面占肺内表面积的99%以上。出生时，胎儿肺迅速从净液体分泌状态（这对胎儿肺的正常发育是必需的）转变为肺泡液量极少的状态。面向气腔的肺泡表面上皮由I型和II型细胞组成。在体重相差约50000倍的一系列哺乳动物物种中，这两种细胞类型的形态特征相当恒定。从跨物种的大小和形状守恒可以推断，I型和II型细胞也具有重要的保守功能。使用多种实验模型，包括全动物、离体肺、离体细胞和培养细胞模型系统，对肺泡离子和液体转运的调节进行了广泛研究，每种模型都有其固有的优缺点。用不同模型系统和多种不同物种获得的结果既有有趣的相似之处，也有一些惊人的差异。有时很难协调用不同模型系统获得的结果。在本节中，主要重点将是正常生理条件下肺泡离子和液体转运的各个方面，强调最新数据并描述肺离子和液体转运不断演变的范式。我们将突出一些未解决的问题，概述用不同模型系统获得的结果的异同，并描述一些复杂且相互交织的调节网络。
