Book - Uterine and tubal gestation (1903) 1-9
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Bandler SW. Uterine and tubal gestation. (1903) William Wood & Company, New York.
|zygote, morula, and blastocyst stages with implantation occurring in week 2.|
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Part I. The Essentials of Uterine Gestation
Chapter IX. The Membrana Chorii
The great growth of the ectodermal cover in the ova of animals has been made known to us by Van Beneden, Duval, Nolf, and especially by Hubrecht, who gave it the name trophoblast.
In 1889 Hubrecht, in examining the placenta of the hedgehog, found a decided resemblance in numerous points to the human placenta. He asked then that the following questions with regard to the human ova should be studied :
- Can, in the earliest stages of human ova, evidences be found of a trophospherical tissue between the villous covered ovum and the inner surface of the decidua reflexa?
- Are there in this tissue blood vessels which receive their supply from those blood vessels which run in the reflexa?
- Can evidences of a trophospherical tissue be found in the serotinal region?
The discussion of the histology of gestation in both uterus and tube shows that the various processes in the development of the human placenta resemble these observed in animal placentation.
It must be noted that these processes follow the steps observed by Hubrecht, Maximow, Opitz, etc. Yet there are still many diverging views as to the origin of the syncytial covering of the villi, as has been also observed in this regard in the investigations in animals.
Selenka and Strahl, in their examination of young human ova, find their views, gained in the examination of animal placentas, sustained— namely, that the syncytial layer originates from the uterine epithelium. "With this view Kossmann and Merttens agree. Eckardt finds that the syncytium originates from the maternal endothelium. Spee states that the syncytium develops from the connective-tissue cells of the decidua. Langhans considers the syncytial layer ectodermal, and the inner layer of Langhans mesodermal. Leopold and Gaisser consider the layer of Langhans to be of mesodermal origin because they find these cells in the mesoderm of the villi. Frankel is uncertain as to the origin of the syncytium in human ova, and finds transitions between the cell of Langhans and cells situated in the mesoderm of the villi. Kastschenko, Minot, Van Heukelom, and Ulesko-Stroganowa consider both layers to be of fetal origin.
Eckardt, who holds that the syncytium originates from the maternal endothelium ( ? ) , states that the capillaries of the decidua which form lacunas under the surface have a varying character. Many possess a distinct growth of the wall elements, which is often so great that he would consider these areas to be sections of glands, were it not for the blood therein contained. We knoAV that, in the decidua menstrualis and graviditatis, blood may enter the glands between the epithelial cells or may break into the glands. The epithelium, which, especially in the neighborhood of the ovum, grows distinctly and shows an enlarged elongated protoplasm, resembles to a certain degree the syncytium. These cells, however, degenerate through the action of the blood and the glands are destroyed or pushed aside. From his description it is quite evident that Eckardt was describing such areas, which he mistook for a growth of maternal endothelium. With these remarks the views of Eckardt may be dismissed.
Merttens found in the particles obtained by curetting sixteen days after the last menstruation a few sections of an ovum with the enveloping decidua. He describes (1) the chorion and the villi. On the latter are cell groups, and between them are found spaces constituting the intervillous space. (2) The spongiosa, containing numerous glands, and (3) the compacta, a pale zone lying between 1 and 2 and containing large pale cells, between which are numerous darkly stained nuclei.
In the compacta he finds large cells and large spaces. Between the large cells syncytial masses are irregularly distributed. The cell spaces are round, long, or irregular, and often empty into the intervillous space. They contain blood and are lined with syncytial masses, which at some points are very thin and at other points quite thick. Where these spaces empty into the intervillous space the syncytial masses continue into the syncytium of the villi. Merttens does not know whether these spaces are glands, vessels, or lymph spaces. They are possibly, however, the lacunae of Hubrecht, Peters, and Opitz.
The epithelia of the glands are like beaker cells, and on their free tips is a half-moon of glycogen. The glands show papillary projections (compare Fig. 145). Merttens believes that the syncytium results through a change of the surface and gland epithelium ( ?). In his Fig. 8 Merttens. represents, in the upper portion, the epithelium of such a gland, and the lower half represents syncytial masses. He believes that the latter result from these epithelial cells, which lose their cylindrical form and unite. From his descriptions and his drawings it is neither clear nor probable that the epithelium changes into final syncytial masses. Besides, this area is taken from decidua particles not connected with the ovum, and at no point can he find the epithelium of the glands contributing in any tvay to the syncytium of the chorion.
On the contrary, this ovum is at the stage where the trophoblast is almost consumed by the growth of the intervillous space, and the cell groups at the end of the villi, which Merttens calls points of union between the villi and the decidua, are really the remains of the trophoblast.
In a very early ovum described by Spee the villi are covered with two layers. The inner, the cell layer of Langhans, he attributes to the ectoderm. The outer layer, the syncytium or adventitia of the ovum, he describes as follows : ' ' This layer is often lifted off from the chorion ectoderm. It appears as a continuous thin streak of protoplasm with more or less closely grouped nuclei arranged in a single row. In the layers of the enveloping zone lying near the ovum are found cells which, through a diffuse staining of the nucleus and through the vacuolar character of the protoplasm, resemble the cell elements of the syncytium very much. In the space between the serotina and the ovum (intervillous space) we find them often close together and not distinctly separated, so that here the early stages of the polynuclear protoplasmatic groups are present. Suclt groups are also found united to the membrana chorii. Concerning their origin opinions differ. I have never observed a mitosis or an amitosis in their nuclei. The idea that the chorion ectoderm furnishes these masses may be set aside because of the sharp division between these two layers by a cuticula. These conditions prove that the syncytial formation does not increase through a division of the nucleus or the cell in the intervillous space. Since, however, an increase in the amount of the syncytial substance occurs within the intervillous space, this can only be explained through a ivandering of already finished masses from the connective tissue of the compacta into the ovum. 1 Epithelial cells cannot be considered as the source, since the maternal cavity surrounding the ovum, even in the earliest stages, shows no epithelial lining, although in the later stages closely pressed glands are present all about the ovum and their epithelium is preserved at least up to the end of the first month." It may be seen that Spee left out of consideration any possible action of the blood upon the ectoderm cells as an aid to the formation of syncytium. His decidua cells, resembling syncytium, are possibly changed trophoblast cells 1 . Cells from without probably form the syncytial covering of the villi and of the membrana chorii, in his opinion. We think they are trophoblast cells of fetal ectodermal origin, acted on by the blood — a possibility which he left out of consideration.
Fig. 36. — Transverse section through the fetal sac or membrana chorii of a four- to five-weeks ovum.
Fig. 36 represents a transverse section through the greatest diameter of the ovum loosely connected with the decidua in the fourth or fifth week of uterine gestation. The centre is a space lined with a double parallel layer of cells arranged in single file. This also loses its parallel arrangement at certain points, where cells of the same character are found in groups several layers deep.
The resemblance of changed decidua cells to the future syncytium is often striking. See foot note, p. 87.
External to these cells, in the entire circumference of the sac, is a substance staining a deeper red and composed of extremely fine, granular, and thin-fibred, cotton-like material. In it, at numerous points, are isolated and grouped cells which look like nucleated red blood cells.
The next stratum is formed of round and oval cells, of the same character as the lining of the central space, but arranged in several somewhat parallel layers. Between these cells is a fine fibre-like substance, like the one just described, but taking a lighter red stain. The outer cells are rounder and more spherical than the inner, and the outermost cells, with a clear protoplasm and distinct nucleus, form a single layer of distinct cells with distinct cell boundaries (36).
The extreme external covering of the membrana chorii is of a plasmodial character, and contains, nuclei of various forms and evidences many vacuoles (Fig. 37). Each vacuole represents the space filled by a trophoblast cell, the nucleus being compressed at one point into a small crescent. At certain points outgrowths are present which contain larger and smaller areas of granular and plasmodial character, the aforementioned distinct cells, blood, and protoplasmatic groups containing small pale cells, small dark nuclei, and nuclei undergoing degeneration. Attached to the membrana chorii and all about it are innumerable villi in all stages of growth, young and old. The older villi present the same structure and possess the same cells, including the nucleated red blood cells, as are found in the chorionic membrane.
Fig. 37. — Vacuoles representing body of trophoblast cells, while the nucleus is a crescent in the circumference. From the membrana chorii of Fig. 36.
The conclusion gained from a comparison of this specimen with the structure of the villi is the following: The single layer of cells immediately under the plasmodium of the chorionic membrane, the spheroidal cells under it, the distinct cells found in the outgrowths, the spheroidal cells in the young villi and in the, cell groups which form the new villi, and the cell layer of Langhans, are identical and represent the ectodermal trophoblast cells. The villi are simply excrescences of the membrana chorii.
When the blood comes in contact with the trophoblast cells it does not coagulate. It does, however, exert a decided influence on the nuclei. Strahl found, in examining the placenta of Galago, that the blood extravasated from the vessels of the uterus is made use of by the fetus, in that the degenerating products of the extravasated blood cells are taken up and absorbed. These products are found in the form of larger and smaller yellow granules in the gland epithelium, which the latter uses in furnishing an iron-containing gland secretion. In the placenta of other animals the blood extravasated from the vessels of the uterus is, taken up and absorbed by the ectoderm cells, and in certain animals the fetus obtains its nutrition because the ectoderm, covering the villus, takes up the substance given off by the uterine epithelium. Merttens observes that Lieberkiihn in the placenta of the dog, and Strahl in the placenta of the mole, find ectoderm cells taking up and absorbing red blood cells. Peters states that Tafani, in the placenta of the cat, found chorion ectoderm cells outside of the placenta taking up red blood cells. We find much blood — that is, red blood cells— in the syncytium. It is also found in the vacuoles. Peters believes that the blood takes part in the changes of the trophoblast nuclei and that its elements contribute to the formation of the protoplasmatic masses known as the syncytium. "Not only the blood plasma, but also the nuclei of red and white blood cells, pass into the composition of these masses." It may be seen in Fig. 315 that the red blood cells change into a detritus and combine, so that finally small irregular areas containing small nuclear remnants result. A gradual destruction of red blood cells takes place, and the presence of leucocyte nuclei may be observed. The plasma, when acting suddenly and in large amounts, causes the trophoblast nuclei to shrink and take on a dark stain. When acting slowly it disintegrates them, flattens them, so that in a resulting homogeneous protoplasm nuclei of all forms may be found. It is evident, then, that the protoplasm of the syncytium is the product of the blood cells, the blood plasma, and the protoplasm of the trophoblast cells. The nuclei of the syncytium are the changed trophoblast nuclei.
Wherever blood comes in contact with fetal cells syncytium results, whether in the decidua or in the intervillous space, so that syncytium really plays the part of an endothelium and at all periods, especially in the later stages, resembles endothelium so closely that it was naturally mistaken for it in nearly all the earlier investigations.
Many observers have noted a brush-like covering on the syncytium, though I have never found it. This striated surface on the syncytial covering of the chorion, and often observed on the isolated polynuclear protoplasmatic masses, appears to Spee to be a sort of fibrillation on the cell protoplasm. He believes that it originates through the influence of a sap current toward the ovum, because such a brush-like fibrillation is found in those places where a regulated transit of products through cells occurs, as in parts of the excretory ducts of the salivary glands and the kidneys on the side toward the connective tissue, and also perhaps in the osteoblasts in the Howship lacuna? of bone.
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Reference: Bandler SW. Uterine and tubal gestation. (1903) William Wood & Company, New York.
Cite this page: Hill, M.A. (2021, July 29) Embryology Book - Uterine and tubal gestation (1903) 1-9. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Uterine_and_tubal_gestation_(1903)_1-9
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