Integrity of lung structure: the role of cells and tissue.

The cellular fine structure of the human lung is described in respect of maintaining a thin barrier between air and blood in the interest of gas exchange. The mechanisms that prevent formation of oedema are discussed. The mechanical design of lung parenchyma and the physiological conditions that allow a very large alveolar surface to be maintained are presented and their importance of a surfactant lining layer for stabilizing this surface is demonstrated.