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The micromechanics of lung alveoli: structure and function of surfactant and tissue components

Authors
  • Knudsen, Lars1, 2, 3
  • Ochs, Matthias1, 2, 3
  • 1 Hannover Medical School, Institute of Functional and Applied Anatomy, Carl-Neuberg-Str. 1, Hannover, 30625, Germany , Hannover (Germany)
  • 2 Member of the German Center for Lung Research (DZL), Biomedical Research in Endstage and Obstructive Lung Disease Hannover (BREATH), Hannover, Germany , Hannover (Germany)
  • 3 REBIRTH Cluster of Excellence, Hannover, Germany , Hannover (Germany)
Type
Published Article
Journal
Histochemistry and Cell Biology
Publisher
Springer Berlin Heidelberg
Publication Date
Nov 02, 2018
Volume
150
Issue
6
Pages
661–676
Identifiers
DOI: 10.1007/s00418-018-1747-9
Source
Springer Nature
Keywords
License
Green

Abstract

The mammalian lung´s structural design is optimized to serve its main function: gas exchange. It takes place in the alveolar region (parenchyma) where air and blood are brought in close proximity over a large surface. Air reaches the alveolar lumen via a conducting airway tree. Blood flows in a capillary network embedded in inter-alveolar septa. The barrier between air and blood consists of a continuous alveolar epithelium (a mosaic of type I and type II alveolar epithelial cells), a continuous capillary endothelium and the connective tissue layer in-between. By virtue of its respiratory movements, the lung has to withstand mechanical challenges throughout life. Alveoli must be protected from over-distension as well as from collapse by inherent stabilizing factors. The mechanical stability of the parenchyma is ensured by two components: a connective tissue fiber network and the surfactant system. The connective tissue fibers form a continuous tensegrity (tension + integrity) backbone consisting of axial, peripheral and septal fibers. Surfactant (surface active agent) is the secretory product of type II alveolar epithelial cells and covers the alveolar epithelium as a biophysically active thin and continuous film. Here, we briefly review the structural components relevant for gas exchange. Then we describe our current understanding of how these components function under normal conditions and how lung injury results in dysfunction of alveolar micromechanics finally leading to lung fibrosis.

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