Morphometry of the human pulmonary acinus

TLDR

Acini are defined as the complex of alveolated airways distal to the terminal bronchioles, beginning with the first‑order respiratory or transitional bronchiole. The study aims to use morphometric data to build an idealized model of human acinar airways linked to existing bronchial tree models. The geometry and morphometry of intraacinar airways were examined on silicone rubber casts from two adult lungs. The study reports that human acini have an average volume of 187 mm³ (SD ± 79 mm³), contain about nine dichotomous generations, feature a decreasing internal airway diameter from 500 µm to 270 µm while the outer diameter stays at 700 µm, show increasing alveolar size and clustering toward the periphery, and have a mean longitudinal path length of 8.8 mm (± 1.4 mm).

Abstract

The geometry and morphometry of intraacinar airways in human lungs were studied on silicone rubber casts from two adult lungs. We defined acini as the complex of alveolated airways distal to the terminal bronchioles--that is, beginning with the first-order respiratory or transitional bronchiole. The morphological properties of pulmonary acini are described. The acinar volume averages 187 mm3 (SD +/- 79 mm3). Intraacinar airways branch dichotomously over about 9 generations (range 6-12). The internal airway diameter falls from 500 micron to 270 micron between acinar generations 0 and 10, whereas the outer diameter (including the sleeve of alveoli) remains constant at 700 micron. Towards the periphery the size of alveoli increases and clusters of alveoli become more numerous. The longitudinal path length of acinar airways (defined as the distance along the ducts from the transitional bronchiole to the alveolar sacs) averages 8.8 mm (+/- 1.4 mm). The morphometric data collected in this study are used to construct an idealized model of human acinar airways that can be related to existing models of the human bronchial tree.