Histogenetic morphotypes of rats respiratory system at the stages of early and late fetogenesis
Authors: Gordienko E. N. , Tseluyko S. S. 
Published: September 2021

Aim. Morphological analysis of the deployment of histogenetic information of pulmonary parenchyma at the stages of late embryogenesis and fetogenesis in laboratory rats within the limits of the norm of reaction with verification according to morphometric criteria of individual morphotypes.

Materials and methods. Comparative morphological study of histogenesis of endodermal derivatives of the lungs of rats at critical periods of intrauterine development – late embryogenesis (day 14 of gestation), and late fetogenesis (day 20 of gestation) was performed using morphometric identification of plane parameters and a complex of plane form factors of epithelial structures of the lung. Morphometric studies were carried out in the Morphometer program on semi-thin sections of the rat lung.

Results. Two critical stages of histogenesis of entodermal beginnings of fetal lungs are described – pseudoglandular and canalicular. The options of discordance of individual development within the response norm are justified. The lungs of the fetus at the pseudoglandular stage and the canalicular stage show significant fluctuations in the plane values of the pulmonary parenchyma, the presence in different individuals of variants of the plane values of entodermal derivatives, which indicated individual morphotypes of the development of the rat lung. At the pseudoglandular stage, in fetus with type I, called “compact”, the total area of the tubular system and the total perimeter are significantly inferior (p<0.001) to the same indicators of the lung II morphotype, designated as “air”. The values of one tubule (the outer perimeter, its area, the dimensions of the X-projection and Y-projection, the length of the epithelial tubes) in type I, on the contrary, are significantly larger than in type II (p<0.01). Among form factors, reliable differences have elongation (FE), squareness (FQ) and equivalent radius (FR) (p<0.01), less significant compactness (FF) and roundness (FC) (p<0.05). The discordance of development is established by a number of reliable values at the stage of late fetogenesis: the area of the tubule (p<0.01), the area of the epithelium of the preacinar department (p<0.001), the value of the outer perimeter of the tubule, the length and, to a lesser extent, the width of the tubule (p<0.05) significantly exceed such type II indicators. In this regard, the dimensions of X- and Y-projections for type I are also increased (p<0.05).

Conclusion. As a result of morphological studies, the development of entodermal derivatives of pulmonary parenchyma at the pseudoglandular stage (day 14 of gestation) and the canalicular stage (day 20 of gestation) in rat fetus was verified; morphometric criteria for assessing the histogenesis of entodermal parenchyma units at critical stages of development have been introduced; comparative analysis of morphometric indices of different individuals in gestation dynamics; individual variants of two morphotypes are objectified – “compact-I” and “air-II” in the process of histogenesis of the fetal lungs.