ONTOGENETIC TRANSFORMATIONS OF BONES OF THE HUMAN ORBIT

Abstract

Introduction. Elucidation of the sources of human orbital bones, clarifi cation of the sequence of their ossifi cation will allow to create a morphological basis for eff ective interpretation of the data of fetal condition monitoring, will contribute to early diagnosis of variants of the structure and possible malformations of the head, organ of vision and related structures.The aim of the study. The aim of this work was to fi nd out the sources of origin, the chronology of ossifi cation, the characteristics of age-related topographic and anatomical changes in the bones of the orbit.Material and methods. 18 series of histological sections of samples of human embryos and pre-fetuses at the age of 4-12 weeks of intrauterine development (4,0-80,0 mm parietal- coccygeal length) and samples of 12 fetuses at the age of 4-9 months of intrauterine development (130,0-450. 0 mm parietal- calcaneal length) using a complex of morphological research methods (anthropometry, morphometry, preparation of histological sections, dissection, three- dimensional reconstruction of series of histological sections and computer tomography, statistical analysis).The study was conducted in accordance with the main provisions of the European Union Convention on Human Rights andBiomedicine (1997), as well as the Helsinki Declaration on Ethical Principles of Medical Research Involving Human Subjects(1964-2008), EU Directive No. 609 (1986), Order of the Ministry of Health of Ukraine dated 23.09.2009 No. 690.The work was carried out within the framework of the initiative research work of the Department of Histology, Cytology andEmbryology of the Bukovinian State Medical University «Structural and functional peculiarities of tissues and organs in ontogenesis, regularities of variant, constitutional, sex and age-related and comparative human morphology». State registration number: 0121U110121. Deadlines: 01.2021-12.2025.The results. The fi rst signs of the appearance of ossifi cation centers around the main nervous and visceral contents of the rudiment of the orbit are determined in 6-week-old embryos in the form of seven cartilaginous bone models, and the fi rst centers of ossifi cation among the rudiments of bones participating in the formation of the orbit are found in the rudiment of the maxilla. In the 6th month of intrauterine development, the processes of ossifi cation of the frontal, sphenoid, ethmoid and maxillary bones begin. At the end of the 8th month of intrauterine development, due to the ossifi cation processes of the lesser wing of the sphenoid and frontal bones, the orbit acquires features of a defi nitive structure.From the beginning of the fetal period of human ontogenesis, ossifi cation of the structures of the sphenoid bone continues, which leads to morphological transformations of the orbit in 5-month fetuses – it is separated from the sphenopalatine and infratemporal fossa by a bone layer, the optic canal is formed, and in 6-month fetuses processes of ossifi cation of the frontal, sphenoid, ethmoid and maxillary bones, and Müller’s orbital muscle changes its structure into a fi brous one.The analysis of the age-related dynamics of the morphometric parameters of the orbit during the fetal period of intrauterine development made it possible to establish the peculiarities of changes in its diameter, circumference and area, which are expressed by mathematical functions: diameter of the orbit, mm = –0. 2285+0.4704*x; circumference of the orbit, mm = –0.2924+1.4595*x; area of the orbit, mm2 = –87.8597+8.0387*x, where x is the age of the human fetus in weeks.Conclusion. The critical periods of the development of the orbit are the 6th month of prenatal ontogenesis, during which there is an uneven growth rate of the horizontal size of the orbit in relation to the vertical one, and its shape returns to the mesoconchal, which was previously observed in fetuses, as well as the 8th month, during which the growth of all parameters of the orbit slows down due to intensive processes of organogenesis of its visceral structures.