EMBRYOGENESIS OF THE HUMAN RESPIRATORY SYSTEM
One of the topical issues of morphology is studying general regulations of development and structural formation dynamics of respiratory system. The aim of the study was to determine peculiarities of the embryogenesis of respiratory system organs during prenatal development in humans. Research was conducted on 22 series of histological specimens of human embryos which were 4,5-8,0 mm of parieto-cocygeal lengths (PLC), and by using complex morphological methods of study (morphometry, histological assessment, three-dimensional reconstruction). It was established that the source of human lungs primordium is a traheopulmonary primordium, which at the end of 4th week of human prenatal development is represented by an odd bud-shaped entity which departs with an acute angle from the ventral wall of the foregut and is located in front of foregut. The beginning of the 5th week of human prenatal development is considered to be a critical period, which holds intensive processes of organogenesis of the respiratory system and is a possible time for the occurrence of some congenital defects or anomalies and structural variants. Sources of pulmonary vessels are islands of intraorgan hematopoiesis and extraorgan main vessels, communication between which occurs during the end of 4th and at the start of 5th weeks of human prenatal development.