Canalicular phase

The lungs of this 20 week fetus show the canalicular phase of development which usually predominates from 16-17 to 25 weeks. The lumina of bronchi and bronchioles have become larger and vascularity has increased as compared with the pseudoglandular phase.

Note that the epithelium lining the airspaces is uniformly cuboidal. During the later canalicular phase differentiation into type I and II pneumocytes will begin.