Fibrous network of the lung and its change with age 1

The remarkable elastic behaviour of the lung entails both continuous tissue stress and a cyclic stress produced by the fluctuating difference between intrathoracic and intra-alveolar pressures throughout the entire span of life. In spite of these potentially disruptive forces, lung structure is preserved by the fibrous connective-tissue proteinscollagen, elastin, and reticulin. These extracellular proteins are characterized by their insolubility, resistance to destruction, and high tensile strength. Collagen and elastin both exhibit elastic behaviour, but great extensibility is a property only of elastin. The most reasonable assumption is that the elastic fibres, therefore, are principally responsible for the elastic behaviour of the lung tissue, but sure proof is lacking. Recently, Carton, Dainauskas, Tews, and Hass (1960) and Wright (1961) have described the nature of the network of elastic tissue in the lung. We sought to describe more fully the roles of collagenous and elastic fibres in the terminal air spaces of the lung, and thus their respective contributions to tissue elasticity and the general elastic performance of the lung. As the study developed, it seemed important to measure the amounts of collagen and elastin in the lung parenchyma and pleura. These findings have been correlated with the age of the subjects and interpreted according to knowledge about tissue elasticity.