[Myocardium development in chick embryo during restriction of external respiration]

The purpose of the present study was to determine the peculiarities of myocardium development in the chick embryos after closure of the half of the eggshell surface on day 11 of incubation. By the end of experimental day 3 (day 14 of incubation), myocardium demonstrated muscle cell hyperplasia and acceleration of their cytodifferentiation. These structural remodeling together with the oxygen blood capacity augmentation and increased vascularization of the intact part of the chorioallantoic membrane, compensate for the oxygen deprivation and provide for the embryo normal growth. By experimental day 7 (day 18 of incubation) the heart structural adaptive resources seem to be exhausted--the morphological signs of cardiomyocyte dystrophy, cardiac and coronary sclerosis, and marked embryo growth retardation were detected.