Formation of pulmonary alveoli and gas-exchange surface area: quantitation and regulation.

New morphometric procedures allow selection of alveoli for analysis in an unbiased manner and then to determine the volume of individual alveoli. The latter, together with the easily measured lung volume, allows the calculation of alveolar number. These new techniques have greatly increased the rigor of the study of the formation of alveoli and the manner in which this process is regulated. This review deals mainly with work based on these new morphometric methods that explore the regulation of the formation of alveoli and hence the size of the lung's gas-exchange surface area. We expect that continued application of these methods, buttressed with experiments at the cellular and molecular level, will result in a fundamental understanding of how the formation of alveoli and the size of the gas-exchange surface area is regulated. This new information holds the promise of translation into the induction of the formation of alveoli for therapeutic purposes.