The growing lung: normal development, and the long-term effects of pre- and postnatal insults

At first sight, adult physicians may feel that intra-uterine lung development is of little interest and importance to them. Paradoxically however, the developing lung impacts more directly on adult practice during foetal life than at any time until the foetus becomes an adult; this is truly an area of interface between adult and paediatric pulmonologists. The lung develops within a foetus which is (usually) within the uterus of an adult, who may be a smoker, or a substance abuser, or may also be receiving treatment for a respiratory condition such as asthma or cystic fibrosis (CF). Some legitimate drug treatment of the mother may adversely impact on foetal lung development. Events around birth and early childhood may also leave a permanent legacy, the fruits of which may appear only in middle age. An appreciation of normal development is fundamental to understanding the effects of the diseases which are described elsewhere in this monograph. The study of events during development may allow new insights into pathophysiological processes in later life, such as foetal ion transport and CF. This chapter therefore emphasizes themes where pathophysiology and disease states are linked. The aim of this chapter is to describe how the lung develops, with a particular emphasis on conditions relevant to adult physicians, rather than trying to give a comprehensive summary of this huge topic. In particular, the many individual mediators and receptors which have been implicated as important in lung development will not be listed in detail. Interested readers are referred to a recent monograph [1]. However, at the moment it is not possible to give a coherent synthesis of the many disparate pieces of evidence accumulating about normal lung growth. It should also be noted that many mediators which have been implicated in pathological processes, such as airway remodelling, also have important roles in normal growth (e.g. transforming growth factor-b). Long term, attempts to promote lung health must begin with the unborn baby, by physicians working with parents.