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=Part I. The Essentials of Uterine Gestation= | |||
==Chapter V. The Trophoblast in the Ova of Animals== | |||
===The Earliest Development of the Ectodermal Extra-Embryonal Area of Animal Ova=== | |||
In discussing the histology of gestation it is important to note that in this field, as well as in that of embryology, many of the most important and valuable points have been learned through the study of like processes in animals. The results obtained in investigations in the latter have been applied more or less closely to the various developmental changes in the human being. Though ofttimes erroneously applied, they have been the source through which many vexed questions have been settled. More recent investigations, however, prove that it is not so much the erroneous applications of the results gained in the study of animals as it is errors made in these observations which have so long delayed a satisfactory conclusion concerning the various processes involved in human placentation. It is necessary, for that reason, to consider first the more recent studies concerning animal placentation, as reviewed by Strahl. | |||
Marchand examined the placentas of rabbits gravid from eight to sixteen days. In the earliest specimens he finds on the ovum a growth of ectoderm elements consisting of two layers: (1) a deeper layer of separated cells and (2) a superficial plasmodial. Since the latter is still covered in part by the zona, it is necessarily of fetal origin. In addition he observes transitions from the cell layer of the ectoderm into the plasmodial. The deeper cells become larger and are arranged in groups. Their cell boundaries disappear, and, through a union of these cells, a plasmodial layer is formed, covering the deeper ectoderm, but, as a rule, distinctly outlined from it. This ectodermal Plasmodium unites with the syncytially-changed uterine epithelium, forming the first connection between the ovum and the uterine wall. In the placenta of nine to ten days Marchand finds blood (1) in the maternal vessels possessing an endothelial lining and (2) in ectodermal spaces in the cell layer. Into these spaces, which possess no endothelium, the blood from the maternal vessels enters. | |||
In the placenta of eleven days few of these unlined ectodermal spaces containing blood remain. Most of them are now lined with a continuous layer of elements rich in protoplasm, which Marchand considers originate from the maternal vessel endothelium ( ?), which has undergone a "syncytial change." | |||
Maximow, in his investigations on rabbit placentae, denies, in contrast to Marchand, the existence of a fetal ectodermal Plasmodium as early as the eighth day. He believes that, when the ovum attaches itself to the uterine wall, the ectoderm consists of only separated cells, which come in contact with the epithelium of the uterus and cause it to degenerate. When the ectoderm, after disappearance of the uterine epithelium, reaches the maternal vessels, the glycogen-containing cells of the uterine connective tissue change to large polynuclear structures. In these cells he finds elements resembling red blood cells in form and color. Only later, when the ectoderm enters into the decidua, does it divide into two layers: (1) one with cell boundaries, the cytoblast, and (2) one without cell boundaries, the plasmodiblast. The latter is found only where the villi come in contact with the glycogen-containing cells, at the ivalls of the maternal vessels. It is not found where the villi grow into the connective tissue between the vessels. From the tenth day on, spaces filled with maternal blood are found in the fetal Plasmodium and there develops an ecto-placenta, into ivhose ectodermal villous formations the mesodermal elements bringing the allantoic vessels enter. | |||
Opitz finds in the rabbit a double ectodermal layer during the process of attachment of the ovum in the uterine wall: (1) an internal layer formed of separated cells, and (2) an external plasmodial layer. The latter causes the uterine syncytium to disappear and aids the attachment of the ovum to the uterine wall freed of epithelium. In the Plasmodium spaces occur into which maternal blood empties from the eroded maternal vessels. From the ovum, ectodermal cell groups enter into this ectodermal Plasmodium, are vascularized, and later become also plasmodial. Those syncytial cells which Marchand considers as resulting from maternal endothelium, Maximow, however, views as ectodermal Plasmodium when found in the fetal portion of the vessels, but considers them in the maternal portion to be endothelial. Opitz considers these cells to be entirely of ectodermal origin. It is to be noted that Maximow and Opitz mention the destruction of the uterine epithelium. Later fetal mesoderm with the allantoic vessels enters into the placenta and on its external surface the remnants of the ectoderm are found as flat covering cells. The epithelium of the uterus plays no part in the development of the placenta, but forms a syncytium which is absorbed by the ectoderm cells. | |||
In Tarsius, Hubrecht finds that the uterine wall, through a change of the connective tissue, forms a trophospongia, betiveen ivhich the glands degenerate. On the growth of the embryonal ectoderm or trophoblast, a mixture of trophoblast and trophospongia occurs, with a decided increase in the volume of this early placental formation. Then the development of the mesodermal villous elements takes place, and the mesoderm villi surround themselves with a trophoblast covering. Between the trophoblast cells lacunae form, into which maternal blood passes. Finally, the trophospongia becomes a thin layer which represents the boundary toward the deeper maternal tissue. | |||
In Tupaja, when the ovum rests upon the uterine wall its ectoderm causes the uterine epithelium to disappear. The trophoblast grows decidedly, with the formation of giant cells, and occasionally forms a combined layer with the uterine epithelium in which maternal and embryonal nuclei lie in a common Plasmodium. The maternal portions degenerate, but the ectodermal tissue is divided into ( 1 ) a deeper layer, the cytotrophoblast, and (2) a superficial syncytial layer, the plasmoditrophoblast, which constitutes only a temporary differentiation. In the uterine wall, in the meantime, the connective-tissue trophospongia is formed; the border between ectoderm and maternal connective tissue disappears, for these tissues infiltrate each other. In this resulting union the trophospongia is overcome by the trophoblast and the maternal blood passes from the maternal capillaries into the embryonal trophoblast spaces. The mesodermal fetal cells, then enter with the allantoic vessels and receive on their external surface a covering of trophoblast. | |||
Although various investigations have shown that the variations in the development of the placenta in different animals are quite unexpected, and that among the individual mammalia, even when closely related, decided differences are found, yet the trend is more toward the view that, as a rule, the syncytium originates from fetal ectoderm. According to Strahl and Selenka, in quite a group of placenta? the uterine epithelium plays no unimportant role. On the other hand, Frankel, as a result of extensive investigations, comes to the conclusion that the higher the organization of the placenta and the more firm the connection between maternal and fetal tissues, so much the less is the maternal epithelium preserved. | |||
He finds that in the rodents and in the insectivorae, whose placentae, of all the animals he examined, stand nearest to the human placenta, the uterine epithelium ceases at the border of the placenta. Only in the pig does it remain. In the cow and sheep the epithelium in the cotyledo shows a tendency to degeneration. In the cat, rabbit, squirrel, guinea-pig, rat, mouse, and mole the uterine epithelium takes no part in the formation of the placenta. A so-called syncytial formation, however, he finds to occur in the most varying tissues. The higher in the animal plane the animal stands, the more does the chorionic epithelium groiv into the maternal connective tissue robbed of its epithelium. | |||
Opitz finds that in the guinea-pig the foundation for the placenta is the fetal ectodermal plasmodium vascularized by maternal vessels. The placentae of the rabbit, the guinea-pig, and the human being agree in that earlier or later the ectodermal surface of the ovum comes in contact with the connective tissue of the uterine mucosa. Finally, between maternal blood and the fetal vessels found in the mesoderm of the villi only one layer of the ectodermal syncytium is left. The apparently great differences are to be explained by the fact that in the rabbit and guinea-pig the projections of ectoderm and mesoderm (the villi) come into union with each other, while in the human being they are always separated. | |||
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Bandler SW. Uterine and tubal gestation. (1903) William Wood & Company, New York.
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Part I. The Essentials of Uterine Gestation
Chapter V. The Trophoblast in the Ova of Animals
The Earliest Development of the Ectodermal Extra-Embryonal Area of Animal Ova
In discussing the histology of gestation it is important to note that in this field, as well as in that of embryology, many of the most important and valuable points have been learned through the study of like processes in animals. The results obtained in investigations in the latter have been applied more or less closely to the various developmental changes in the human being. Though ofttimes erroneously applied, they have been the source through which many vexed questions have been settled. More recent investigations, however, prove that it is not so much the erroneous applications of the results gained in the study of animals as it is errors made in these observations which have so long delayed a satisfactory conclusion concerning the various processes involved in human placentation. It is necessary, for that reason, to consider first the more recent studies concerning animal placentation, as reviewed by Strahl.
Marchand examined the placentas of rabbits gravid from eight to sixteen days. In the earliest specimens he finds on the ovum a growth of ectoderm elements consisting of two layers: (1) a deeper layer of separated cells and (2) a superficial plasmodial. Since the latter is still covered in part by the zona, it is necessarily of fetal origin. In addition he observes transitions from the cell layer of the ectoderm into the plasmodial. The deeper cells become larger and are arranged in groups. Their cell boundaries disappear, and, through a union of these cells, a plasmodial layer is formed, covering the deeper ectoderm, but, as a rule, distinctly outlined from it. This ectodermal Plasmodium unites with the syncytially-changed uterine epithelium, forming the first connection between the ovum and the uterine wall. In the placenta of nine to ten days Marchand finds blood (1) in the maternal vessels possessing an endothelial lining and (2) in ectodermal spaces in the cell layer. Into these spaces, which possess no endothelium, the blood from the maternal vessels enters.
In the placenta of eleven days few of these unlined ectodermal spaces containing blood remain. Most of them are now lined with a continuous layer of elements rich in protoplasm, which Marchand considers originate from the maternal vessel endothelium ( ?), which has undergone a "syncytial change."
Maximow, in his investigations on rabbit placentae, denies, in contrast to Marchand, the existence of a fetal ectodermal Plasmodium as early as the eighth day. He believes that, when the ovum attaches itself to the uterine wall, the ectoderm consists of only separated cells, which come in contact with the epithelium of the uterus and cause it to degenerate. When the ectoderm, after disappearance of the uterine epithelium, reaches the maternal vessels, the glycogen-containing cells of the uterine connective tissue change to large polynuclear structures. In these cells he finds elements resembling red blood cells in form and color. Only later, when the ectoderm enters into the decidua, does it divide into two layers: (1) one with cell boundaries, the cytoblast, and (2) one without cell boundaries, the plasmodiblast. The latter is found only where the villi come in contact with the glycogen-containing cells, at the ivalls of the maternal vessels. It is not found where the villi grow into the connective tissue between the vessels. From the tenth day on, spaces filled with maternal blood are found in the fetal Plasmodium and there develops an ecto-placenta, into ivhose ectodermal villous formations the mesodermal elements bringing the allantoic vessels enter.
Opitz finds in the rabbit a double ectodermal layer during the process of attachment of the ovum in the uterine wall: (1) an internal layer formed of separated cells, and (2) an external plasmodial layer. The latter causes the uterine syncytium to disappear and aids the attachment of the ovum to the uterine wall freed of epithelium. In the Plasmodium spaces occur into which maternal blood empties from the eroded maternal vessels. From the ovum, ectodermal cell groups enter into this ectodermal Plasmodium, are vascularized, and later become also plasmodial. Those syncytial cells which Marchand considers as resulting from maternal endothelium, Maximow, however, views as ectodermal Plasmodium when found in the fetal portion of the vessels, but considers them in the maternal portion to be endothelial. Opitz considers these cells to be entirely of ectodermal origin. It is to be noted that Maximow and Opitz mention the destruction of the uterine epithelium. Later fetal mesoderm with the allantoic vessels enters into the placenta and on its external surface the remnants of the ectoderm are found as flat covering cells. The epithelium of the uterus plays no part in the development of the placenta, but forms a syncytium which is absorbed by the ectoderm cells.
In Tarsius, Hubrecht finds that the uterine wall, through a change of the connective tissue, forms a trophospongia, betiveen ivhich the glands degenerate. On the growth of the embryonal ectoderm or trophoblast, a mixture of trophoblast and trophospongia occurs, with a decided increase in the volume of this early placental formation. Then the development of the mesodermal villous elements takes place, and the mesoderm villi surround themselves with a trophoblast covering. Between the trophoblast cells lacunae form, into which maternal blood passes. Finally, the trophospongia becomes a thin layer which represents the boundary toward the deeper maternal tissue.
In Tupaja, when the ovum rests upon the uterine wall its ectoderm causes the uterine epithelium to disappear. The trophoblast grows decidedly, with the formation of giant cells, and occasionally forms a combined layer with the uterine epithelium in which maternal and embryonal nuclei lie in a common Plasmodium. The maternal portions degenerate, but the ectodermal tissue is divided into ( 1 ) a deeper layer, the cytotrophoblast, and (2) a superficial syncytial layer, the plasmoditrophoblast, which constitutes only a temporary differentiation. In the uterine wall, in the meantime, the connective-tissue trophospongia is formed; the border between ectoderm and maternal connective tissue disappears, for these tissues infiltrate each other. In this resulting union the trophospongia is overcome by the trophoblast and the maternal blood passes from the maternal capillaries into the embryonal trophoblast spaces. The mesodermal fetal cells, then enter with the allantoic vessels and receive on their external surface a covering of trophoblast.
Although various investigations have shown that the variations in the development of the placenta in different animals are quite unexpected, and that among the individual mammalia, even when closely related, decided differences are found, yet the trend is more toward the view that, as a rule, the syncytium originates from fetal ectoderm. According to Strahl and Selenka, in quite a group of placenta? the uterine epithelium plays no unimportant role. On the other hand, Frankel, as a result of extensive investigations, comes to the conclusion that the higher the organization of the placenta and the more firm the connection between maternal and fetal tissues, so much the less is the maternal epithelium preserved.
He finds that in the rodents and in the insectivorae, whose placentae, of all the animals he examined, stand nearest to the human placenta, the uterine epithelium ceases at the border of the placenta. Only in the pig does it remain. In the cow and sheep the epithelium in the cotyledo shows a tendency to degeneration. In the cat, rabbit, squirrel, guinea-pig, rat, mouse, and mole the uterine epithelium takes no part in the formation of the placenta. A so-called syncytial formation, however, he finds to occur in the most varying tissues. The higher in the animal plane the animal stands, the more does the chorionic epithelium groiv into the maternal connective tissue robbed of its epithelium.
Opitz finds that in the guinea-pig the foundation for the placenta is the fetal ectodermal plasmodium vascularized by maternal vessels. The placentae of the rabbit, the guinea-pig, and the human being agree in that earlier or later the ectodermal surface of the ovum comes in contact with the connective tissue of the uterine mucosa. Finally, between maternal blood and the fetal vessels found in the mesoderm of the villi only one layer of the ectodermal syncytium is left. The apparently great differences are to be explained by the fact that in the rabbit and guinea-pig the projections of ectoderm and mesoderm (the villi) come into union with each other, while in the human being they are always separated.
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Reference: Bandler SW. Uterine and tubal gestation. (1903) William Wood & Company, New York.
Cite this page: Hill, M.A. (2024, April 18) Embryology Book - Uterine and tubal gestation (1903) 1-5. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Uterine_and_tubal_gestation_(1903)_1-5
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
