Features of early morphogenesis of the human venous system in normal and pathological conditions

During human ontogenesis, three circulatory systems function sequentially: the vitelline, placental, and pulmonary. The vitelline system is transient and is replaced by the placental circulation, which persists until the end of intrauterine development. Аim - to clarify the features of early morphogenesis of the human venous system under normal conditions and in pathology, in order to identify critical periods of its formation and detect prerequisites for congenital cardiovascular malformations. Materials and methods. The study was carried out on 33 series of sagittal, frontal, and horizontal sections of human embryos and prefetuses aged 4-10 weeks of intrauterine development (crown-rump length 6.0-38.0 mm), stained with hematoxylin and eosin. For the analysis of venous structures in 10 fetuses aged 4-8 months, macromicroscopic dissection, microscopy, and modern imaging techniques with three-dimensional (3D) reconstruction and morphometric analysis using ImageJ software (NIH) were applied. Results. The most rapid development occurs in vessels belonging to the placental circulation and the portal system, which is evolutionarily related to the regressed vitelline circulation. These venous channels appear before the placenta is fully formed. At early stages, venous vessels have thin walls, and their lumen often exceeds the diameter of the aorta. The umbilical vein initially represents the widest vessel with a thick wall, later becomes equal to the aorta, and before obliteration is thinner than it. The complex morphogenesis of the venae cavae determines a predisposition to anomalies. Conclusions. In embryos with a crown–rump length of 6.0-7.0 mm, the most developed vessels are those of the placental circulation (umbilical arteries and vein). Venous vessels initially lag behind arteries in development but subsequently exceed them in diameter. Disturbances of morphogenesis may result in anomalies such as double vena cava or umbilical vessel defects, increasing the risk of congenital heart malformations. The study was conducted in accordance with the principles of the Declaration of Helsinki. The study protocol was approved by the Local Ethics Committee for all participants. The authors declare no conflict of interest.