Physiological atresia, or fetal occlusion, is an epithelial vegetation arising at a certain stage of embryonal fetal life in some organs of esophageal, respiratory and urogenital system as well as in natural openings of the head--the lid slit, external nasal openings, external and internal acoustic meatus. In parallel, tubal organs close to open later, i.e. recanalization takes place. In view of this, epithelial "plugs" in the larynx and external nasal openings have a positive biological role making a temporary obstruction for amniotic fluid penetration into the viscera. Plug-induced difference of pressure between closed nasal cavity and open oral cavity in reflexes of mouth opening helps horizontal adjustment of the processes of the palate bone. This is important for formation of the hard palate. Before appearance of functioning muscles of the soft palate, epithelial plugs in the external nasal openings block nasal cavity. If the plugs were absent, fetal swallowing movement would be impossible, as amniotic fluid would outpour through the nose. Epithelial adhesions in external nasal openings as well as in the larynx and esophagus are temporary structures contributing to formation of palatine shape and establishment of fetal functions.