Book - Uterine and tubal gestation (1903) 1-2
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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 II. The Embedding of the Ovum in the Guinea-Pig
A. Uterus of the Guinea-Pig
The uterus of the guinea-pig is six centimetres long and consists of two muscular layers, an external longitudinal one closely connected with the peritoneum, and an internal circular one. Sometimes, within the latter, are found isolated bands of longitudinal fibres.
Between the two muscular layers is a broad zone of loose connective tissue, and in this are found the continuations of the vessels which enter through the longitudinal layers at the mesometral area. All the larger vessels are in the circular layer. Their walls lose the muscularis and their continuations then enter the specific parenchyma of the uterus, where they appear as capillaries or simple endothelial channels.
Fig. 1. — Half-schematic section of the uterine horn of a guinea-pig. (v. Spee.)
The uterine lumen is lined with a single uninterrupted layer of cylindrical epithelial cells ; no cilia are clearly seen. This epithelial layer descends into the connective tissue at numerous places, into glands lined with a low epithelium. The peripheral ends of the glands are twisted and extend up to the circular layer. An active increase of epithelial cells through mitosis takes place only in the end areas of the glands, so that here the regenerative stations for the uterine epithelium are to be sought. In other areas of the uterine lining the epithelial cells have lost the power to produce new cells. This is the case in animals in ivhom the epithelium plays no part in the formation of the placenta.
The connective tissue consists of two zones separated by a transition zone. (1) A peripheral zone surrounding the twisted gland ends and consisting of spindle or branching cells with intervening spaces, resembling a loose reticular connective tissue. (2) A central compact zone situated between the straight excretory ducts of the glands. In the implantation of the ovum only this area is invaded. Extremely numerous mitoses, and the varying appearance and thickness of their tissue, are proofs of active changes and an increased tissue change. Since at points not important the strongest cell increase may be found, the conclusion is justified that the life of the connective-tissue cells of the uterus is short. There are no spindle-shaped or branching cells here as are found in the peripheral zone.
Fig. 2. — Cells of the compact zone with the epithelial lining of the uterine lumen of the guinea-pig. (v. Spee.)
The cells of the central zone (Fig. 2) lie like the cells of stratified epithelium. They are polygonal, close together, generally separated by sharp contours, which are probably intercellular spaces. The most firmly uniting basis is furnished by the capillary network, for a real connecting factor among the elements of the connective tissue, especially of the compacta, is not present. The normal relation is preserved by the firmly united epithelium and the circular muscular layer, between which lie the two layers of connective tissue.
B. The Embedding Op The Guinea-Pig's Ovum
In 1883 Spee stated that on the sixth day post coitus the ovum of the guinea-pig is an oval germinal vesicle one-tenth of a millimetre in diameter, surrounded by a zona pellucida and lying free in the uterine cavity (Fig. 3). The cell wall of the vesicle, the germinal layer, consists, in the region of the ovum's equator, of a single layer of very flat cells. At the two poles the wall seems thicker. At one pole the cell wall of the vesicle is stratified and forms a prominence into the cavity of the vesicle, the Germinal Prominence of Hensen or the Placental Pole (P. P.). At the other pole (the Opposite Pole of Spee) the germinal layer consists of a single layer of cubical cells, constituting the Implantation Pole (LP.). It forms after implantation that summit of the ovum into which the embryonal sphere enters and in which the embryo develops.
Fig. 3. — Ovum of guinea-pig free in the uterine cavity. Ovum with zona. Note. — The lettering of Pig. 3 is reversed, (v. Spee.)
The zona is preserved up to the beginning of the seventh day post coitus and can be readily seen on the free germinal vesicle. The cubical cells of the Implantation Pole send prolongations of their cell bodies through the zona and can enter into direct relation with the epithelial lining of the uterus before the zona is lost finally to the ovum, and may so furnish the first connection ivliich leads to implantation. These prolongations have been seen only in the region of the Implantation Pole. The short period, during which the prolongations of the Implantation Pole hold the ovum fixed to the uterine epithelium, however, has not been observed.
When the ovum is first attached to the uterine epithelium the zona is present (Fig. 3a), but disappears in a very short time, for it is not seen in embedding ova. Probably the Implantation Pole prolongations perforate it and cause its disappearance at these points. The rest is probably rubbed off. In irrigating a uterus for ova, Spee once found the cell body of an ovum and an empty zona with a hole large enough to have permitted the former to slip out. Acids dissolve the zona, and, as these were often used in fixing the specimens, the fact that no zona was found in the youngest ova which had entered the uterine wall does not prove that the ova were embedded after removal of the zona. The ova during implantation, however, are so closely surrounded by uterine tissue that between them there is no room for a zona, and so in all probability the ovum does not take the zona with it into the uterine wall.
The Embedding or Implantation of an Ovum includes the group of processes which result in the ovum entering from the uterine cavity into the connective tissue of the uterine wall. The processes antedate the formation of the placenta and are distinct from the processes of placental formation, hut the first evidences of the latter follow immediately upon implantation. In the guinea-pig, ova are never implanted at a point at which or in whose neighborhood signs of circulatory disturbances (excessive collection of tissue exudation in the interstices of the subepithelial connective tissue, or a grouping of red blood cells in these interstices), or evidences of a throwing off of tissue into the uterine lumen, are noted. Only such areas are selected as are normal and whose tension, dependent on tissue sap, is even, which fact coincides with the observation that the uterine lumen at the selected point always shows a surprisingly smooth epithelial lining without folds.
Fig. 3a. — Ovum of guinea-pig in its first adhesion to the uterine epithelium. Ovum still possesses its zona. (v. Spee.)
The ovum is almost always embedded on the anti-mesometral side, corresponding to the fundus uteri in the human being, and beings about 6 days, 8 to 12 hours post coitus, seldom later at the end of the seventh day. The time left for embedding is 4 to 8 hours. Its beginning is known with a possible variation of about 6 hours. The ovum does not increase in size before its embedding, and measures with the zona only 0.1 millimetre, without the zona 0.08 millimetre, while the uterus is 6 centimetres long. As often only one or two ova are present and as their location is not macroscopically evident, only series sections divulge the various points. If the ovum is already through the uterine epithelium, it is seen with difficulty because of its small size. One may readily imagine the labor involved in obtaining the present unbroken series illustrative of the various stages, a work on which Spee has been engaged for the last ten years.
Fig. 4. — b, capillary ; v, vacuole ; c, cavity in ovum. Ovum of guinea-pig par tially embedded, showing disappearance of the uterine epithelium, (v. Spee.)
• The cells of that pole which leads all other parts in its entrance into the uterus (I. P.) send prolongations through the zona shortly before the implantation period, and render contact and exchange with the uterine epithelial cells possible, even before the zona is gone. These prolongations cause the first adhesion of the ovum to the uterine epithelium (Fig. 3a).
The uterus plays a passive role in implantation of the ovum. The ovum enters the uterine wall and a correspondingly large space of uterine tissue disappears.
The uterine epithelium shows no sign of growth.
The uterine epithelium of just that area in contact with the ovum disappears (Fig. 4).
In Fig. 4 the ovum is 6 days and 10 hours post coitus, and evidences no zona. A thin cell layer (a) surrounds for a distance the cavity (e) of the ovum on one side, but is not distinct on the other side. The solid portion of the ovum consists of large round cells which are not surrounded by a cell covering. Only at a is there a flat cell which stands in continuity with the cell membrane enclosing the cavity of the ovum (e). The membranous portion of the ovum contains two small vacuoles (v).
Fig. 5. — Further stage in embedding of ovum, showing changes wrought in the connective tissue compacta. (v. Spee.) x, two cells of the ovum which are embedded on the opposite side.
The central cavity is lined with a non-celled coagulation substance, which has divided the cavity into two parts, probably a postmortem change. The external surface of the solid area is not covered by a specially differentiated layer of flat cells. The solid group of cells represents the placental pole. The cavity e represents the germinal cavity. The part of the ovum near the connective tissue, at the Implantation Pole, is the cell wall of the cavity, the germinal membrane. The space between the cells, and the thin layer near the connective tissue, later becomes filled with cells, forming a solid ovum.
Decided changes occur in the connective tissue which makes room for the ovum. These changes for a long time are such as may be considered a necrosis and a paralysis of the life processes of the connective-tissue cells (Fig. 5).
Fig. 5 shows a double embedding at two points vis-a-vis. The ovum evidences no cavity. The ovum is already deep in the wall and the uterine epithelium is interrupted in the circumference of the ovum. The surrounding connective-tissue cells have changed in that a half-moon arranged row of connective-tissue cells of a stronger stain has been formed. The cells of the ovum are much larger than the connective-tissue cells. To the left at x two cells of the ovum are united to the uterine epithelium, and two others, not distinctly seen, have perforated the uterine epithelium. The single layer about the ovum at I. P. is the germinal layer plus the implantation pole. The cell group at the placental pole has grown into, and filled out, the germinal vesicle, but the ovum is not enlarged. Therefore the ovum now evidences no cavity. The sharp contour at o bounds the connective tissue sharply and is independent of the cell body of the ovum. That the cells of the ovum dissolve the epithelium with which they come in contact, is seen in its early stages at x, where four cells are present. The connective-tissue cells about the ovum are large and polygonal with sharp contours and of epithelioid form. This form also is found in certain areas away from the ovum, and is there dependent on other influences than the ovum. This change in the cells extends, and this area is called the Implantation Area. During this peripheral extension the cells nearest to the ovum show other changes in the nuclei. They stain darker. This is due to a process of dissolution, and as a matter of fact the nuclei nearest to the ovum are already smaller and mitosis has ceased in the immediate circumference of the ovum.
Fig. 6. — Further stage of embedding of guinea-pig's ovum, showing the connective tissue compacta about the ovum destroyed by the bio-chemical influence of the ovum. (v. Spee.) c, centre of ovum ; G, embryonal sphere.
Fig. 7. — A stage of embedding one-half hour later than Pig. 6 (v. Spee). more highly magnified. G, embryonal sphere. The ovum is surrounded by a symplasmatic zone.
The connective-tissue cells are fluidified by a form of digestion. The disappearance of mitosis for a considerable distance about the ovum, the dissolving of the connective-tissue cells immediately about the ovum, while at a distance normal cell division takes place, show that the destruction of uterine tissue is due to a biochemical process dependent on the ovum (Fig. 6).
Fig. 6 is still further embedded, and in four-fifths of its circumference is a single layer of cells, the germinal layer. This is connected at the placental pole with a solid mass, the germinal prominence, which fills the space surrounded by the germinal layer. The Implantation Pole is situated on either side of 8.
In Fig. 7 the ovum is situated half in the epithelium and half in the subepithelial connective tissue. The ovum is sharply bounded from the connective tissue. It is surrounded by a symr plasmatic zone in which a histolytic process causes the contours and nuclei of the connective-tissue cells to disappear, as if the ovum were a poison. The ovum consists of a covering layer and a contained mass (G) of large cells containing fat. A small space separates the ovum, in part, from the connective tissue (C. t).
Fig. 8. — Almost embedded ovum surrounded by fluid resulting from fluidified connective tissue cells, (v. Spee. )
The ova 6, 7, and 8, though differing only about half an hour in age, produce great changes in the connective tissue. Ovum No. 6 is about three-fourths embedded. Ova 7 and 8 were found in the same uterus. Only in 8 is a growth of the ovum, as compared with 5, evident. Important are the connective-tissue changes, first in the cells of the Implantation Area, and, second, in the boundary line which faces the ovum. Ovum No. 8 is almost embedded and several of its cells are on a line with the uterine epithelium. A comparison of ova 6 and 8 evidences two differences, which show the two varying functions in two different parts of the ovum, (1) the part consisting of the external layer, a derivative of the germinal layer, and the Implantation Pole; (2) the cell mass at the Placental Pole. In the circumference of the Implantation Pole the connective-tissue cells beneath the epithelium disappear or degenerate. The cells at the Placental Pole do not destroy the uterine tissue, therefore the hole in the uterine epithelium at the Placental Pole of ovum 8 is not enlarged.
Fig. 9. — Ovum entirely under the uterine epithelium, a.s., assimilation border of the implantation area ; y, embryonal sphere ; H, fluid space about ovum, (v. Spee.)
In the Implantation Area the connective-tissue cells and the nuclei become large. The chromatin of the nuclei becomes grouped on the inner surface of the nuclear membrane, but the nuclear centre is pale. Peripheral to the implantation zone numerous mitoses are observed and are also found in the vessel endothelia. A dense tissue results and the cell interstices disappear, as may be seen in Pig. 9. This very peripheral area has no meaning with regard to implantation or to placental formation.
In Fig. 5 the cells nearest the ovum stain darker and are smaller. In Fig. 6 a contour divides the connective tissue near the ovum from the ovum, but instead of numerous cells and nuclei we see a fibred, granular mass, a group of closely gathered nuclei without cell contours. In Fig. 7 some nuclei are still well stained, but lie in a fibred, granular mass in which no cell contours are evident. A symplasma has been formed through the dissolution of the connective-tissue cells of the implantation zone which is sharply marked off from the ovum.
The ovum is then almost surrounded by fluid residting from these changed cells (Figs. 8, 9, 10).
In Fig. 8 the symplasma is separated from the ovum by the space H, which is wider than in Fig. 7. In the periphery are smaller, darker cells ready to join the symplasma. Here, then, is the assimilation boundary of the symplasma, The space H is filled with a fluid into which the edge of the symplasma passes over gradually. This constitutes the dissolution boundary of the symplasma. The contents of the space H are a thin emulsion which is under pressure, causing the circular contour of the symplasma in Fig. 9.
Fig. 10. — A further stage, showing demarkation of the symplasma, thus limiting the assimilation of future areas, n, free nuclei in the symplasma. (v Spee.)
The fluidifying of the symplasma occurs not only at its edge but in its substance, and becomes porous and filled with vacuoles which contain fluid (Figs. 8 and 9). In Fig. 9 the vacuoles are present in large number. At the assimilation boundary at a. s. are seen darker, smaller cells. At / (Fig. 10) is seen a sharp demarkation of the symplasma of the implantation zone which limits the assimilation of future areas. The nuclei of the last assimilated cells lie at this area of separation, in short simple rows. They furnish almost -the same picture as the nuclei in the syncytial or plasmodial formations in the placenta of other animals. The symplasma degenerates and the original boundary of H formed by it disappears.
Fig. 11. — Ovum entirely embedded in connective tissue compacta, showing spaces (H) in the fibred tissue about the ovum. The fibred tissue about the ovum contains numerous granules. This is a middle stage between the normal compacta and the final fluid symplasma. (v. Spee.)
Along the epithelial lining the subepithelial cells become smaller, and darker areas of separation appear between them and the epithelium leading up to complete loosening of the latter. The subepithelial cells, fluidifying, form lacunae in the subepithelial connective tissue (Fig. 12).
This fluid, through diffusion or possible absorption by the ovum, makes place for the ovum, which only now begins to grow quickly. Later, at the boundary between necrotic and healthy tissue, a real granulation tissue is formed as an active reaction to the entering ovum (Fig. 12).
In the transition zone appear granular cells, which increase from Fig. 9 on, and eventually forming a characteristic zone in the far periphery, in which the cells also seem clouded. Soon a separation of the implantation area from the connective tissue occurs at the transition zone through great growth of cells in the peripheral areas, and through a stoppage of growth and degeneration in the implantation area. The capillaries pass through this boundary and on their walls are grouped connective-tissue cells. They are numerous at the point of separation, so that the space bet. epith. and conn, tissue
Fig. 12. — g, embryonal sphere ; n, free nuclei of the syrnplasina ; b.c, capillaries. The ovum has grown. Ovum has a cavity, except at implantation pole, where the embryonal sphere is in contact with the external layer of the ovum, (v. Spee.) Completely embedded, growing ovum.
wall looks like a granulating wound surface of endothelial channels. The space about the ovum is gradually rilled with granulation tissue in the next twelve hours. Seven days post coitus the ovum has groAvn considerably (Fig. 12). The Placental Pole evidences a papulation of the germinal layer which gives this end a half-cylindrical groove, due to two lateral folds. The ovum now evidences a cavity, except at the Implantation Pole, where the embryonal sphere is in close contact with the external membrane of the ovum.
Seven days thirteen and one-half hours post coitus the ovum has grown large (Fig. 13). The space between the embryonal sphere and the Placental Pole has grown decidedly, so that the ovum is a long, cylindrical vesicle, with its Placental Pole in contact with the uterine epithelium.
The investigations of Spee show that the ovum, of the guineapig, not grown since its fecundation, destroys like an injurious parasite the uterine epithelium and the subepithelial connective tissue to make place for itself in the uterine wall in which it is embedded, and that only after this does it enter into a symbiotic connection with the uterus, which connection finds its expression in the formation of a placenta. The same occurs with the human ovum.
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Reference: Bandler SW. Uterine and tubal gestation. (1903) William Wood & Company, New York.
Cite this page: Hill, M.A. (2021, April 12) Embryology Book - Uterine and tubal gestation (1903) 1-2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Uterine_and_tubal_gestation_(1903)_1-2
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