[Respiratory and non-respiratory functions of the lung]

With the development of higher organisms, the problem of gas exchange of each single cell had to be resolved. Nature gave preference to the development of a specific organ for gas exchange (lungs, gills) as opposed to a system of gas exchange involving the whole organism. In vertebrates, the latter has been developed only in lungless salamanders (Desmognatus fuscus) and in the embryos of the oviparous species. Mammalian embryos also do not use their lungs during the prenatal period, however, in contrast to the oviparous species gas exchange is performed via the maternal respiratory apparatus. The transition from the pre- to the neonatal period is more problematic in mammals than in oviparous species. The critical situation is caused by the fact that mammalian lungs must be inflated within a comparatively short period of time. In oviparous species, however, the development of lung respiration lasts several hours. Several lines of evidence indicate that lungs are also involved in blood pressure changes occurring during the perinatal period. In this context the pulmonary regulation of bradykinin and prostaglandin metabolism has been emphasized. It has been recognized that lungs of adults serve not only as a gas exchange organ, but are involved in the synthesis, activation or inactivation of substances which exert an influence mainly on blood pressure. In this function, lungs are especially suitable due to their position between the venous and arterial circulation. Therefore, it is not surprising that disturbances in the pulmonary function result in manifold pathological processes.