Embryogenesis of the perineum

Background. The study of projection-syntopic and spatio-temporal patterns of embryonic development in its entirety provides an understanding of the formation of morphological structures of the organism, and the latter, in turn, helps in determining the discreteness of critical periods of fetal development. It is the tracking of bookmarks of various organ complexes and body systems during critical periods of development that makes it possible to obtain the most extensive and in-depth understanding of the immanent properties of the formation of integration units of the human body. Purpose: to investigate the features of the morphogenesis of the cloaca division mechanism. Establish the initial elements of the future structures of the male crotch area. Methods. To achieve the goal, a series of sections of 15 embryo preparations, aged from 4 to 8 weeks of intrauterine development (4.0-19.0 mm in parietal-caudal length) were used. The following research methods were used: microscopy, three-dimensional modeling, morphometry. Results. The expediency of dividing the cloaca into three departments is substantiated. The membranous cloaca is located opposite the cloacal membrane. Mesodermal folds of the cloaca are present on the sides of the membranous cloaca. The cranial part of the cloaca passes into the primary gut and is surrounded on the sides by the mesodermal tissue of the side wall of the embryo's body. Dorsally, the cloaca is limited by the mesodermal tissue of the dorsal wall of the embryo body, which is a continuation of the mesodermal folds of the cloaca. Its endodermal covering is formed from one or two layers of columnar epithelium, which in some places is separated by an intercellular space. The membrane of the cloaca is formed by several layers of cells. The deeper epithelial layers are derived from the endoderm, the superficial ones are the ectoderm, and consist of one or two layers of light flattened cells. The superficial, denser mesodermal tissue of the cloacal folds is located medially and limits the width of the cloacal membrane. Conclusions. 1. The division of the cloaca into three parts is associated with the differential growth of the growing ventral part and the non-growing craniodorsal part of the cloaca area. 2. In the initial stages, the ventral part is compressed by zones that do not grow and do not increase in volume, however, the growth and expansion of the ventral part of the cloacal area causes the division of the latter into genitourinary and recto-rectum segments and forms the genital tubercle.