Book - Uterine and tubal gestation (1903) 1-12
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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 XII. The Placenta
That part of the decidua covering the embedded ovum, plus the scar of Reichert, forms the capsularis, or decidua reflexa. That part of the decidua in which the ovum is embedded, and on which the ovum rests in its early stages, is the serotina. Here the main changes between the ovum and villi on the one hand, and the decidua and maternal blood on the other hand, take place. The remainder of the decidua is the vera.
The villi in the entire periphery of the ovum depend for their growth and development on connection with the maternal decidua and blood. At the end of the first month the villi are evenly distributed over most of the periphery of the ovum. With the growth of the ovum in the next two months there is a stretching of the capsularis, which, however, grows likewise, so that it is not much thinned except at its summit. There is, however, in these two months a constantly slighter connection of the vessels of the capsularis with the maternal vessels of the vera and serotina. In addition the fetal vessels w T hich enter the membrana chorii through the adherent band establish closer and more immediate relations with the villi at the serotina, for the abdominal pedicle is at this point.
As a result we distinguish two divisions in the chorion: (1) that in which new villi cease to develop and in which formed villi gradually degenerate and atrophy — the chorion Iceve; and (2) that in which the villi increase hugely in number and size, the area, at the serotina — the chorion f rondo sum.
The chorion frondosum forms the placenta. The growth of the uterus in the first three months is independent of the growth of the ovum, and the uterus undergoes eccentric development. Therefore the area of the serotina increases in extent. The ovum grows of its own accord, and as a result the area of the chorion frondosum increases in extent and keeps pace with the growth in extent of the serotina. Septa, of decidua extend between villi and groups of villi, due to the irregular invasion of the serotina. As the ovum grows in the first three months it is covered by capsularis (Fig. 39). Though the capsularis at the end of the third month covers an ovum as large as a goose egg, it is fairly thick except at its summit, and is in contact with the decidua vera in its entire circumference. During the fourth month the capsularis unites at all points to the vera and its nourishment ceases except at its oase. The area where capsularis at its base joins the serotina and vera is known as the Border Zone and constitutes the boundary of the ' ' placental area" in the first three months. The base of the capsularis unites last with the vera. Septa of serotinal decidua extend between villi and groups of villi, especially at the point where capsularis, serotina, and vera join, and there lie close to the membrana chorii, forming a maternal border or margin to the placenta — i.e., at the border zone the decidua is supposed to extend up to and touch the membrana chorii as Winkler's Plate.
In the early three months, up to the formation of the placenta, even though the uterus grows actively, the growing chorion frondosum and the base of the chorion Jaeve extend into vera and split it into two layers ( ?). The lower layer becomes serotina and the upper layer is added to the capsularis. From the end of the third month on, the uterus enlarges passively through growth of the ovum. It is scarcely possible that the edge of the growing placenta then likewise splits the vera into two layers to any extent, but in its growth it will extend, strictly speaking, not upon vera, but upon the base of the capsularis which has united to vera. The villi do not atrophy on every point of the capsularis. They may persist on the part of the capsularis nearest to the vera and serotina. When capsularis unites to vera these villi may grow through the united capsularis and vera. As a rule the loosest union between capsularis and vera is at this point and so the loosest union of villi and placenta to decidua is at this point.
Three groups are observed in mammalia, as regards the character of the chorion.
(1) The chorion is smooth and is attached to the uterine mucosa, which is rich in vessels. The chorion takes from the large epithelial cells of the uterus nourishment for the embryo.
(2) The chorion has projections or villi. An allantois approaches the chorion, and contained umbilical vessels enter the villi. The chorion and the mucosa are closely connected. In the pig, for instance, numerous projections, rich in vessels, fit into smooth depressions in the mucosa, in which open the uterine glands. In labor the villi and the uterine mucosa are separated without loss of mucosa substance.
(3) At one or more parts of the chorion a placenta develops composed of placenta fetalis and placenta uterina. In the sheep, cow, and ruminants a subdivision exists. Numerous small placentre or cotyledones are present. The villi are covered with flat cells and the depressions of mucosa are lined by cylindrical cells. The latter develop a so-called uterine milk for the nourishment of the fetus. All other mammalia with a placenta evidence a very close connection betiveen the maternal and fetal parts, and in labor a decidua is cast off. Here a syncytium forms the separation between the villi and the maternal blood.
Fig. 43. — Low-pressure drawing of uterus and placenta at full term, showing the close but uneven attachment of the placenta, two-thirds of actual thickness. To the right the villi are on the muscularis. To the left (marked Decidua) there is spongiosa. In hardening a separation formed between compacta and spongiosa at this point.
Fig. 44. — Utero-placental junction at full term. 8 and the other spaces are maternal vessels. Villi are projecting into maternal sinuses. U.W., uterine wall infiltrated with fetal cells, especially with the very dark giant syncytial masses. Of the four septa between the villi, the two outer are "adherent villi," the two inner are decidual septa. Some of the sinuses are possibly glands with lost epithelium.
Fig. 45. — High-power drawing of an area in Fig. 44, showing the invasion of maternal tissue by fetal cells even at full term, and also the entrance of villi into the uterine veins through the blood current.
Fig. 46. — High-power drawing of placental villi of Fig. 44, showing the free syncytial masses and the chorionic syncytium to be identical with the syncytial giant masses of Fig. 45.
The invading trophoblast and syncytial cells have a decided poiver of wandering. These wandering cells are often found singly, entering between the muscle and the connective-tissue bundles, in the lymph spaces and often in the blood vessels.
Through pressure they are often reduced to thin, long, spindleshaped forms, and, when found, the muscle fibres between appear to be changed forms of the latter. In the earlier periods, round or polyhedral cells with very large, round or irregular, long, darkly-staining nuclei are found and have been generally mistaken for decidua cells. Their nuclei are often very large and on degeneration contain vacuoles. 1
In the specimens (Figs. 43, 44) on page 95 is seen a section through a placenta and the uterine wall at full term. The villi are very closely grouped. The uterine wall evidences large sinuses and is thoroughly infiltrated with fetal cells and many giant syncytial masses 1 of the same character as the syncytial covering of the villi. In the drawing may be seen four extensions between the uterine wall and the main mass of the placenta. Between the extensions loose and attached villi, as well as free syncytial masses, are present. The two middle extensions belong to the uterine wall, but they are thoroughly infiltrated with fetal cells. On their sides and at their tips villi are attached, sending at these points their cells in the uterine wall.
The two outer extensions are the so-called adherent villi firmly embedded in the uterine wall, and their tips are outlined by more closely grouped and more darkly stained ectodermal cells. It is from points like these that the ectodermal cells and the giant cells invade most deeply the uterine wall, as may be seen in Fig. 44. The spaces between these extensions represent the mouths of the maternal sinuses which send their blood into the intervillous space.
In the case of normal uterine gestation villi do not project into the arterial openings of the intervillous space. They do, however, project normally not only at the border sinuses, but at all the serotinal points into the veins alone. The villi are of normal structure and often so numerous that they occlude the vein lumina. They are frequently very long and follow the course of the veins for a considerable distance, so that in the uterus villi may be found in direct contact with the uterine muscle or, better, in the veins of the uterine muscle (Fig. 45).
From the very earliest period of trophoblastic development trophoblast cells may be carried into the maternal circulation through the blood lacuna? and the blood capillaries. In the latter stages the trophoblast cells invading the decidua, eroding the vessels, and destroying the decidua furnish still further opportunities for the entrance of fetal cells into the maternal circulation. When the intervillous space is well defined and is limited in its entire circumference by the point of union of the decidua vera and the capsularis (decidua refiexa), a still further opportunity is furnished to syncytial masses, cell groups, and even villi to be carried through the veins into the maternal circulation. In the still later periods and at full term, villi projecting into the maternal veins may be carried off, and the fetal cells which have invaded the decidua and the uterine Avail, and which even up to the last days of gestation continue to enter the maternal vessels, may readily enter the maternal blood current. In eclampsia such elements have so frequently been found in the cirsulation, and especially in the lungs, that they have been considered the cause of this affection. They have, however, been proved to be rather the result than the cause, for Schmorl and others have found them in these locations in perfectly normal cases.
- Many consider these placental giant cells to be of decidual origin So does Spee.
The important fact remains that from the very earliest moment, not only in the primary intervillous space but in the fullyformed intervillous space, as well as through the vessels of the uterine decidua and ivall, fetal cells are continually entering the blood of the mother.
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Reference: Bandler SW. Uterine and tubal gestation. (1903) William Wood & Company, New York.
Cite this page: Hill, M.A. (2021, June 15) Embryology Book - Uterine and tubal gestation (1903) 1-12. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Uterine_and_tubal_gestation_(1903)_1-12
- © Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G