Rat lungs show a biphasic formation of new alveoli during postnatal development

Tschanz, Stefan A.; Salm, Lilian; Roth-Kleiner, Matthias; Barré, Sébastien; Burri, Peter Hermann; Schittny, Johannes (2014). Rat lungs show a biphasic formation of new alveoli during postnatal development. Journal of applied physiology, 117(1), pp. 89-95. American Physiological Society 10.1152/japplphysiol.01355.2013

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Roughly 90% of the gas-exchange surface is formed by alveolarization of the lungs. To the best of our knowledge, the formation of new alveoli has been followed in rats only by means of morphological description or interpretation of semiquantitative data until now. Therefore, we estimated the number of alveoli in rat lungs between postnatal days 4 and 60 by unambiguously counting the alveolar openings. We observed a bulk formation of new alveoli between days 4 and 21 (17.4 times increase from 0.8 to 14.3 millions) and a second phase of continued alveolarization between days 21 and 60 (1.3 times increase to 19.3 million). The (number weighted) mean volume of the alveoli decreases during the phase of bulk alveolarization from ∼593,000 μm(3) at day 4 to ∼141,000 μm(3) at day 21, but increases again to ∼298,000 μm(3) at day 60. We conclude that the "bulk alveolarization" correlates with the mechanism of classical alveolarization (alveolarization before the microvascular maturation is completed) and that the "continued alveolarization" follows three proposed mechanisms of late alveolarization (alveolarization after microvascular maturation). The biphasic pattern is more evident for the increase in alveolar number than for the formation of new alveolar septa (estimated as the length of the free septal edge). Furthermore, a striking negative correlation between the estimated alveolar size and published data on retention of nanoparticles was detected.

Item Type:

Journal Article (Original Article)


04 Faculty of Medicine > Pre-clinic Human Medicine > Institute of Anatomy
04 Faculty of Medicine > Pre-clinic Human Medicine > Institute of Anatomy > Functional Anatomy
09 Interdisciplinary Units > Microscopy Imaging Center (MIC)

UniBE Contributor:

Tschanz, Stefan A., Salm, Lilian, Barré, Sébastien, Burri, Peter Hermann, Schittny, Johannes


500 Science > 570 Life sciences; biology
600 Technology > 610 Medicine & health




American Physiological Society




Johannes Schittny

Date Deposited:

13 Oct 2014 11:07

Last Modified:

05 Dec 2022 14:35

Publisher DOI:


PubMed ID:


Uncontrolled Keywords:

alveolarization bulk alveolarization continued alveolarization disector late alveolarization lung development microvascular maturation stereology





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