[How chicken embryo survives after half of shell is sealed?]

The goal of this study was to explore the development of the gas transport systems in chick embryos after half of the shell surface is closed on incubation day 11. By the end of day 3 of the experiment (incubation day 14), the vascular reduction in the chorioallantois under the covered zone is fully compensated by the vessel dilatation and growth in the intact half. In parallel, the oxygen capacity of blood elevates and hematopoiesis increases: the indices of hematocrit, hemoglobin, and erythrocyte count increase by half. The development of the left ventricular myocardium accelerates through the myocyte hyperplasia and their more mature ultrastructure. The obtained data indicate that hypoxia accelerates the embryonic development and leads to earlier and faster differentiation of the gas transport systems. However, the efficiency of antihypoxic responses is limited by the upper bound of capillary density in the chorionic respiratory network. After 1 week of the experiment (incubation day 18), the total vascular volume in the chorioallantois is halved relative to control, while the arterial walls substantially thicken in the open part, which increases the peripheral resistance. Atherosclerosis and dystrophy of cardiomyocytes developed in the left ventricle. These general hemodynamic abnormalities are accompanied by a notable embryonic growth inhibition. Thus, the structural compensation of the gas transport systems in the experiment becomes exhausted and cannot provide for increasing metabolic demands of the growing embryo.