The development of the thoracic duct lymphangions in the prenatal period of human ontogeny]

This paper concerns structural and functional organization of the human lymphatic system during the prenatal period. For the first time the data is presented on the development of thoracic duct based on the concept of lymphangion as a structural and functional unit of a lymphatic vessel. The formation of the duct is considered in connection with structural changes of its wall and variants of duct roots fusion. The following stages are distinguished in the development of the thoracic duct: valval segment stage, protolymphangion, and lymphangion.     

Development of the ductule system of the epididymis in the prenatal period of human ontogeny

In 285 human embryos, prefetuses, fetuses and newborns by means of a complex of morphological methods, development of the epididymal canalicular system has been studied. The anlage of the epididymal canalicular system is stated to appear in embryos 13.0-17.0 mm long (the 6th week of development) and is presented as an accumulation of epithelial cells and primary germ cells between reducing glomeruli and mesonephric canaliculi. The canalization process of the cellular accumulations and their transformation into real canaliculi takes place during the first half of the prefetal period (the 8th week of development). Further growth and development of the epididymal canaliculi takes place in the craniocaudal direction and by the end of the prefetal period (the 12th week) the canaliculi of the head are already formed, they have a twisted course; within the limits of the body and tail they are yet poorly differentiated and their course is nearly straight. During the fetal period of ontogenesis, further differentiation of the epididymal parts occurs and structure of their canaliculi becomes more complex. They acquire a twisted course in all the parts of the organ; by the end of the fetal period the form and structure of the epididymal canaliculi resemble those of the definitive organ.     

Development of the hemomicrocirculatory bed of the human gonads during the prenatal period of ontogeny

The formation of the organospecific hemomicrocirculatory bed of the ovaries and testes has been studied by a complex of light, transmissive and scanning electron microscopy in 3--9-month-old human fetuses. The change of the diffusive protocapillary bed is secured by: 1) reduction of some protocapillaries; 2) appearance of secondary capillaries from the growth buds of the preceeding microvessels; 3) formation of arteriolar and venular links of the hemomicrocirculatory bed from the protocapillaries at the expense of differentiation of the developing paravasal connective tissue into cellular elements of the muscular and adventitial tunics. The secondary blood capillaries of the human gonads are predominantly formed intraendothelially. During the prenatal ontogenesis presence of the secondary blood capillaries of somatic uninterrupted type is specific for the human gonads.     

Development of the neural apparatus of the human pancreas in prenatal ontogeny

In human embryos, prefetuses and fetuses from 6 to 40 weeks of development 82 preparations of the pancreas have been studied; 39 series of slices of the human embryos have been impregnated after Bielschowsky-Boeke. For the first time the nerves grow into the pancreas anlage in embryos of 16 mm long (6 weeks). The main sources supplying the pancreas with the nerves in the period studied are nervus vagus, celiac, hepatic, splenic, right adrenal, superior mesenteric and intermesenteric plexuses. Three stages in formation of the innervational apparatus of the pancreas are distinguished during the intrauterine development. The first stage is characterized by beginning of the nerve growing into the pancreas anlage. For the second stage an increased development of the intraorganic innervational apparatus and appearance of the all main sources of the organ's innervation are specific. The third stage is characterized with an increased differentiation of receptor zones in various parts of the pancreas. The development of the pancreatic innervational apparatus by the time of birth is not completed.     

Synapses of the human brain in early prenatal ontogeny

Synaptogenesis in presumptive cerebral cortex was studied in 7-8 week human embryos by electron microscopy. The first synapses in the regions studied appeared in 7-week embryos. These synapses were detected only in the marginal zone of the developing human cerebral cortex, where they were localized on the somas and processes of the young Cajal-Retzius' neurons. A functional role of early embryonic synaptogenesis in the developing human cerebral cortex is suggested.     

Development of dendritic spines in the piriform neurons of the cerebellar cortex in human prenatal ontogeny

The submicroscopic investigation on developmental peculiarities of the dendritic spines in the piriform neurons of the cerebellar cortex has been performed during the human prenatal ontogenesis. The process of morphogenesis of the spines of the tertiary dendrites in the piriform neurons is demonstrated to start rather early--on the 24th week of embryogenesis and goes through three successive stages: 1) formation of a long cytoplasmic processes deprived of any membranous specialization; 2) formation of the terminal spinal head, making synapses with parallel fibers of the cerebellar cortex; 3) definitive stage. A suggestion is made that differentiation processes of the spines depend on inductive influence of the parallel fibers of the cerebellar cortex.     

Development of the microcirculatory bed of the human tongue in the prenatal period

Morphofunctional regularities of formation and development of the blood microcirculatory bed in the human tongue have been studied in the prenatal period of morphogenesis. 119 human embryos and fetuses at the age of 5 weeks--9 months have been investigated. A complex of methods have been used: common histological (hematoxylin--eosin, after van Gieson and Mallory), injection of the lingual vessels with 20% suspension of Indian ink--gelatin, transmissive electron microscopy. General regularities of organogenesis, stages of the blood microcirculatory bed development and peculiarities of the process on formation of the primary protocapillary lingual blood bed are revealed. Regularities in structure of the terminal vascular constructions are studied for each structural element of the organ--mucosal membrane, muscles, glands, lingual tonsil. For these elements at the ultrastructural level certain features of the organic specificity in the structure of the blood microcirculatory bed links are determined.     

The anatomicohistological characteristics of the formation of the mucosa of the human small intestine in the prenatal period of ontogeny]

The time, when the first villi appear, is defined. Quantitative composition, percent content, height of the villi of the mucous membrane in all parts of the small intestine during various periods of the intrauterine development are presented. In 17-week-old embryos at the level of the duodenum the first villi are noted and their formation in the middle part of the intestinal tube is revealed. By the 8th-9th weeks of development they appear at the level of the caudal part of the intestine. This demonstrates asynchronism of their formation in the cranio-caudal direction. The periods of their intensive growth in height in the first part of the intestine correspond to 8-10, 12-16, 24 weeks of the fetus age, in the second part--to 8-10, 18-20 weeks, in the third--to 10-12, 16-18, 26-28 weeks. These periods alternate with an abatement in growth intensity, which is connected with an increasing width of the villi themselves, with amount of newly formed villi and with changes of the intestinal tube diameter. The form of the villi is rather variable.     

Sex differences in the development of the thyroid gland in human prenatal ontogeny

A comparative study of the thyroid gland development in the human male and female embryos and prefoetuses was carried out. The development of incretory part of the testicles was shown to occur earlier than the differentiation of follicles in the thyroid gland and the appearance of colloid in it. Sexual differences were noted in the appearance of follicles, connective tissue, nerve fibres in the thyroid gland (earlier in the male foetuses). The processes of organ differentiation in the male foetuses were more active than in the female ones during the whole prenatal period of development. A suggestion is put forward that the sexual hormones of embryonic testicles influence the thyroid gland differentiation.     

Genetic determination of growth processes in the peripubertal period of human ontogeny

Chronological peculiarities of genetic determination of three factors of physical development in different phases of peripubertal stage of human ontogenesis were studied. The differences between sexes are explained by the hypothesis of mutual "clearing off" of X-linked genes' effects. This hypothesis is confirmed by the coincident dynamics of two indices--of additive genetic effects in boys and of nonlinear genetic effects in girls. The results point to autonomous nature of genetic determination of head's morphological structures, which is more expressed in boys. The component partitioning of the phenotype variance of the individual scores of linear discriminant functions revealed steady decrease across the peripubertal stage in the level of genetic determination of the variability of children's belonging to the different age periods. In the whole, the results indicate the existence of marked genetic determination of physique's growth and development in a stage under study of human ontogenesis.     

Development of the seminiferious tubules and rete testis during the prenatal period of human ontogenesis

The sources of origin and the peculiarities of formation of the seminal ducts and rete testis during the prenatal period of ontogenesis in man were studied. It has been established that the seminal duct sand the ducts of the rete testis form from the cellular cords of the coelomic epithelium and the primordial germ cells which appear simultaneously in the septum of the testis and the primordial germ cells which appear simultaneously in the septum of the testis and central part of its parenchyma in the embryos, 13.0--17.0 mm long. By plastic and graphic reconstruction, as well as by methods of subtle preparation under binocular microscope MBC-I control it was revealed that the seminal ducts anastomosed between themselves both within the limits of one and the adjacent lobules. The ducts of the rete testis do not form anastomoses, but superimpose over one another, creating an impression of a rete. Approaching the tunica albuginea they merge, continuing into the cuctuli efferentes testis.     

Pathology of amniogenesis in the early prenatal period of human development

Morphological and, in a number of cases, cytogenetical investigation has been performed in 420 intact embryonal sacs and in embryos 7-8-week-old, obtained at spontaneous abortions (272) and at tubal pregnancy (148). Among these cases 202 (48.1%) intact empty embryonal sacs, 75 (17.9%) embryos with panorganodysplasia, 25 (6%) embryos with isolated developmental defects and 118 (28%) phenotypically normal embryos have been revealed. Pathology of amniogenesis such as aplasia or hypoplasia of the amniotic cavity is noted in 136 (32.4%) cases. Among 75 embryos with panorganodysplasia anomalies such as hypoplasia of the amniotic cavity in combination with a partial extra-amniotic++ position of the embryos in exocelom (10.7%), aplasia (5.3%) or hypoplasia (17.3%) amniotic peduncle is present in 43 (57.3%) observations. Out of 40 such cases at spontaneous abortions, cytogenetically investigated, in 27 (67.5%) chromosomal disorders (tetraploidy, triploidy, autosomal trisomy and monosomy) are revealed. Aplasia and hypoplasia of the amniotic cavity are considered as pathology of histogenesis at the tissue stage of the early human ontogenesis, that most evidently occurs as a result of asplasia, destruction or anomaly of embryoblast during the first phase of gastrulation on the 7th-11th day of the intrauterine development.     

The microscopic anatomy of the human pharyngeal tonsil in the postnatal period of ontogeny

Histological sections of the pharyngeal tonsil (PhT) have been investigated in 55 corpses of persons of both sex and various age, that had no disease connected with lesions of the PhT by the time of their death. The aim of the work is to determine relative areas of each structural element of the PhT in comparison to the whole section area taken as 100%. The PhT lymphoid tissue reached its maximal relative development at the first childhood. Then the lymphoid tissue area in the PhT histological sections decreases gradually, making already in the second mature age one half of the tonsil section area, and in the elderly age--nearly one-fourth. The decrease of the relative lymphoid tissue area takes place at the expense of decreasing area of the lymphoid nodules. The relative area of the connective stroma increases inversely to the relative decrease of the lymphoid tissue area parameters. The germinative centers in the lymphoid nodules are absent in newborns and old persons. The greatest value of the relative area of the germinative centers falls to the early infancy. The lymphoid nodules with the germinative centers, according to their relative area during all age periods, besides the newborn period, the second mature, elderly and old age periods, essentially exceed the area, that occupy the nodules without the germinative centers on the PhT sections.     

Development of the paravascular bed of the vessels of the human heart during the prenatal period of ontogenesis

The paravascular bed of the cardiac vessels has been studied in 128 human fetuses at the age of 3-9 lunar months. Anatomical and histological techniques have been used, morphometrical analysis has been carried out. The paravascular bed of the cardiac wall vessels begins to form from the vascular epicardial network and from the paraneural vessels in 5-month-old fetuses. The paravasal longitudinal tracts are the first to form (the venous ones preceed the arterial). During the seventh month the nutritive vessels and the intramural networks of the main cardiac arteries and veins develop. The formation of the paraarterial bed is connected with the vascular diameter and with thickness of the arterial walls. Certain regularities in development of the venous paravascular bed are defined. By the beginning of the 8th month there are all main components of the paravascular bed of the cardiac vessels.