Microcorrosion casting of the human respiratory acinus.

Microcorrosion casts demonstrating the respiratory acini of human lungs were produced using Tensol Cement No. 70 (a methyl methacrylate mixture). Lung casts were made from foetuses of 19 weeks' gestation to term, a child of 5 years and two adults. Tensol Cement No. 70 was found to infuse the most peripheral airspaces without tissue penetration and could be airdried. Attempts using Batson's medium were hampered by permeation of the airway walls and inability to withstand airdrying. Despite the use of autopsy material, good cell impressions were seen. At 19 weeks' gestation, the respiratory acinus is simple with only two or three generations of rather tubular respiratory bronchioles. In later intra-uterine development, the number of generations of intra-acinar airways increases and the most peripheral airspaces expand to form initially shallow but later cup-shaped saccules. At all ages, the proximal airways of the acinus have regularly-spaced deep cell impressions suggesting a cuboidal/columnar epithelium while the distal airspaces have less frequent shallow cell impressions suggesting a flattened epithelium. Measurements of the maximum diameter of the most peripheral airspaces show an approximate doubling of size between 19 weeks' gestation and term and a further doubling by the age of 5 years.