Postnatal growth of the mouse lung
Amy, R.W.; Bowes, D.; Burri, P.H.; Haines, J.; Thurlbeck, W.M.
Journal of Anatomy 124(Pt 1): 131-151
1977
ISSN/ISBN: 0021-8782 PMID: 914698 Document Number: 114604
Morphological changes occurring in the lungs of mice from birth to adult life were followed using light microscopy and scanning electron microscopy. Alveoli are absent at birth, and the gas exchanging units of the lungs at this time are primary saccules, characterized by smooth walls and a wide capillary system, frequently forming a double layer. During the subsequent 3-4 days, the smooth primary saccule wall is modified by the elevation of very low secondary crests, appearing as narrow ridges. The network of elastic and collagen fibers probably play a key role in alveolar development. Secondary crests rapidly elongate after the 4th day, subdividing the primary saccule into alveoli, and alveolar multiplication is substantially complete by the 14th postnatal day. Pores of Kohn, infrequent in the first 10 days of postnatal life, increase rapidly in number after the 14th day and have an adult configuration by day 22. Lung weight remains constant in the 1st day of postnatal life. The rate of increase in lung weight is greatest during the next 5 days of postnatal life, reflecting cellular proliferation that occurs in the walls of the primary saccules.