Some features of intrauterine development of capillaries in the head and neck area

BACKROUND: The development of capillaries in human embryogenesis is a multi-stage process influenced by genetic factors and signaling pathways, which is of interest in studying the mechanisms of vascular bed formation in the prenatal period of human development. AIM: To study the development of capillaries in the embryonic and early fetal periods and determine the morphological prere­quisites leading to the formation of developmental defects. MATERIAL AND METHODS: The biomaterial of 50 embryos and fetuses from 4 to 12 weeks was studied. A histological and electron microscopic examination of the specimens was performed in the axial plane at the level of both jaws and neck. The volume fraction of capillaries and muscle fibers in the structure of the sternocleidomastoid muscle was determined. Data on the volume fraction of each component were presented as median and interquartile range. Quantitative analysis was performed using the Kruskal–Wallis and Mann–Whitney methods with Bonferroni correction. RESULTS: At the 4th week, a capillary network began to develop from the mesenchyme, which took on a complete form by the 8th–10th week. The proportion of capillaries increased from the 6th to the 10th week, and by the 12th week it decreased. A statistically significant pattern of changes in the ratio of the proportion of capillaries in muscles with the volume fraction of muscle fibers itself was revealed. As the mass of the muscle fibers themselves increased, the proportion of capillaries in it decreased significantly from 1.92 (1.77; 2)% at 4–6 weeks of embryogenesis to 0.25 (0.23; 0.26)% at 10–12 weeks. CONCLUSION: The critical period for the development of capillaries is the intrauterine period from the 4th to the 12th week of development, when in the structure of muscles as an organ, the vascular component first prevails over the muscular component itself, and then sharply decreases.