Surface view of an injected human lung shortly before the fetus becomes viable.
These figures of a silicon-rubber-injected fetal human lung illustrate the precocious development of filaments (future alveolar ducts) of the pulmonary acini. In contrast, there is a long delay in the differentiation of respiratory bronchioles. The former are the first to sustain respiration.
D001980:Bronchi / Q000033:anatomy & histology / Q000196:embryology; D006801:Humans; D008168:Lung / Q000033:anatomy & histology / Q000196:embryology*