Pre-hatch lung development in the ostrich

We studied development of the ostrich lung using light microscopy as well as electron microscopy techniques. At E24, the lung comprised a few epithelial tubes, interspersed with abundant mesenchyme with scattered profiles of incipient blood vessels. Between E24 and E39, the epithelial thickness was reduced by 90% from 13.5 ± 0.41 μm to 1.33 ± 0.014 μm (mean ± SD, respectively). Atria were evident at E32, and by E35, the first portions of the blood-gas barrier (BGB) measuring 3.41 ± 1.12 μm were encountered. Gas exchange tissue was well formed by E39 with atria, infundibulae, air capillaries and a mature blood-gas barrier (BGB). BGB formation proceeded through the complex processes of secarecytosis and peremerecytosis, which entailed decapitation of epithelial cells by cutting or pinching off respectively and by E39, the BGB was thin at 2.21 ± 1.21 μm. Vascular remodeling by intussusceptive angiogenesis was a late stage process mediated by intraluminal pillars in the pulmonary vasculature.

► Epithelial attenuation during ostrich lung development follows processes of cell cutting similar to those described in the chicken. ► Between embryonic days E24 and E39, the epithelial thickness is reduced by 90% from about 13 μm to less than 3 μm. ► Atria formation is evident from E32 while first portions of thin blood-gas barrier (BGB) form by E35. ► Blood vessel augmentation and remodeling proceeded through intussusceptive angiogenesis. ► A remarkably thin BGB was formed by E39, in readiness for hatching at E40.