HISTOGENESIS AND MOLECULAR DEVELOPMENT OF THE LUNG IN NEW ZEALAND WHITE RABBIT (Oryctolagus cuniculus)

Abstract

In investigating fetal organ development, fetus of the rabbit was one of the furthermost frequently handled as a model in animal investigational research. During the second half of gestation in rabbit fetuses thorax volume (TV) was the predictive factor for assessment of normal development. Concerning these fetuses, evaluation of lung development was more applicable in the 20th–29th gestational days for experiments. A large internal surface area in which the inspired air and capillary blood got in close contact to each other was specified by the lung tissue. Consequently, an efficient gas exchange was occurred. A cycle of separate but overlapping developmental processes happened to reach this target. The anlage of the left and right lungs appeared as an outpouching of the foregut endoderm during organogenesis. A repetitive process of outgrowth and branching pattern (branching morphogenesis) was occurred in each lung bud. Consequently, all of the future airways were formed mainly during the pseudoglandular stage. Repetitive airspace septation would lead to tremendous increase of the gas exchange surface area in both late fetal and postnatal lung development leading to the formation of alveoli. The first air-blood barriers were appeared and surfactant production began during the canalicular stage.