Stretch and Grow: Mechanical Forces in Compensatory Lung Growth. Mechanical Forces in Compensatory Lung Growth.

How does the lung grow? The answer to this question remains fragmentary despite the recent explosion of information concerning the cellular and molecular events that influence developmental and compensatory lung growth. In particular, we lack an adequate understanding of how the escalating number of molecular signals and mediators known to act on individual components of the lung are coordinated to form the complex three-dimensional architecture that fully meets functional requirements. We understand even less about the altered coordination of growth and remodeling events in adaptation to a loss of functioning lung units caused by injury or disease. While normal post-natal lung maturation reaches its limit at somatic maturity, it is apparent that in the face of destruction of some lung units, growth and remodeling may be re-initiated in the remaining units by the appropriate institution of mechanical stimuli leading to partial or complete restoration of gas exchange capacity. What signals trigger growth re-initiation? How do the signals act on the constitutive components to effect balanced alveolar septal growth while minimizing distortion and maximizing functional benefit? The objective of this chapter is to compare the characteristics of developmental and post-pneumonectomy (PNX) growth in order to (a) illustrate key principles in the regulation of growth and remodeling in relation to mechanical tissue stress and strain and (b) interpret the innate potential for lung re-growth in the context of structure-function relationships with respect to the whole organ.