Peculiarities of embryogenesis of human respiratory system
One of the topical issues of morphology is studying general regulations of development and structural formation dynamics of respiratory system. Aim of the study was to determine peculiarities of respiratory system organs' embryogenesis during prenatal development in human. In order to achieve the aim, we have studied 22 specimen's series of human embryos with 4,5-8,0 mm of parieto-coccygeal length (PCL) by using a complex of morphological research methods (histological methodic, morphometrics, graphic and three-dimensional computer reconstruction, and statistical analysis). It has been found that with the absence of external signs of lung division on lobes, bronchial tree already begins to branch, which concludes that process of entodermal laying of lungs is slightly ahead in its development, comparing to mesenchymal, and consequently plays a major role in formation of lungs. It was also established that starting from the 5th week there is an asymmetry in size of right and left lungs primordium's, as well as in main bronchi branching. The source of human lung primordium is a tracheo-pulmonary primordium, which at the end of 4th week of fetal development is represented by odd bud-shaped entity which departs with an acute angle from ventral wall of the foregut and is located in front of foregut. Beginning of the 5th week of human prenatal development is considered to be a critical period, which holds intensive processes of organogenesis of respiratory system and is possible time for occurrence of some congenital defects and structural variants. Sources of pulmonary vessels are islands of intraorgan hematopoiesis and extraorgan main vessels, communication between which occurs during end of 4th and start of 5th weeks of prenatal development.