Book - Uterine and tubal gestation (1903) 1-8
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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 VIII. The Chorionic Villi
The ectodermal cover of the ovum has the name chorion-ectoderm to distinguish it from the ectoderm in the amniotic cavity, a part of which takes part in the embryonal formation.
This ectodermal cover evidences a great growth of cells in the entire circumference of the ovum, forming what is called the trophoblast. These trophoblast cells invade the decidual compacta. The capillaries of the compacta dilate into lacunae or wide spaces. The blood breaks through the lacuna? and now, at this early time, maternal blood comes in contact with fetal ectodermal trophoblast cells. The maternal blood when it comes into contact with the trophoblast cells changes them to large polynuclear cells, consisting of the protoplasm of several cells in which the trophoblast nuclei of these cells form a polynuclear group. Such groups and likewise large mononuclear cells result from the action of the blood on the trophoblast. Such resulting cells are called syncytial cells, mononuclear or polynuclear. They line, too, the lacuna? in the circumference of the trophoblast.
The trophoblast cells are constantly spreading in the periphery of the ovum, entering further and further into the decidua. They have a destructive action on the decidual cells ; they reach capillaries and vessels and enter the latter. Wherever they open lacuna? or vessels the outpoured blood changes the trophoblast cells with which it comes in contact into syncytium. As a result the trophoblast is divided and subdivided into small islands consisting of groups and masses of trophoblast cells. The cells on the outside of these groups are changed by blood to syncytium. Such groups of trophoblast cells surrounded by syncytium are the future villi. Subsequently mesoderm develops in the interior of these trophoblast islands or "cell groups" and we have young villi (Fig. 31). Later most of the trophoblast cells are displaced and disappear with the exception of a single row situated immediately beneath the syncytium. This single row, composed of large distinct cells with pale protoplasm and large nuclei, is called the cell-layer of Langhans. In the centre of such groups is thy developed mesoderm, and the so-called villi are now formed, but as yet no capillaries are present. Such extensions, composed of a centre of mesoderm and a periphery of Langhans cells, with the latter surrounded by syncytium, are the final villi in whose conuective-tissue centre capillaries finally develop which are connected with the capillaries of the fetus.
When the trophoblast first develops and. extends into the maternal compacta its margin is irregular and. serrated (Fig. 20). As capillaries on the compacta are opened syncytium is formed wherever blood touches the trophoblast cells. The points of trophoblast furthest advanced extend continually into new compacta, destroy it, and open more capillaries. In this way the process is carried on through a constantly increasing periphery. As a result long, irregular, branching, finger-like extensions of trophoblast project out from the trophoblast layers situated immediately on the external layer of mesoderm produced by the mesoderm slit. These layers are, too, changed to syncytium and cell layer of Langhans. Under them the mesoderm also grows and displaces most of the trophoblast cells. The resulting continuous outer wall of the ovum from which the finger-like extensions (villi) project is called the membrana chorii (Figs. 25, 27,29, 296, 3(M).
Fig. 31. — Schematic representation of a later stage of placental development than Fig. 24, showing young villi. (Peters.)
To the inner surface of the membrana chorii is attached the adherent band, or abdominal pedicle. It is a band of mesoderm which has grown continually longer. In it is the allantoic duct. Through it pass the vessels of the fetus to enter the mesoderm of the membrana chorii and the mesoderm of the villi.
The capillaries which develop in the villi unite with the vessels of the fetus in the membrana chorii. Thus, through the medium of the adherent band, fetal blood is brought into the villi. The villi are surrounded by maternal blood and so an exchange between fetal and maternal blood is carried on through the two layers of epithelium covering the villi (Fig. 31).
In the Fourth Week of Uterine Gestation, when the original trophoblast capsule is consumed, the ovum is loosely connected ivith the decidua by only a few adherent villi. The following remarks concern such an ovum, covered with chorionic villi,
Fig. 31a. — A well-developed villus showing cell layer of Langlians with "cell group or pillar" at its tip. These cell groups are trophoblast cells. The villus is covered with syncytium which is very thin over the "cell group."
aborted in the fourth week. Its attachment in the uterus must have been exceedingly loose, for the numerous and countless villi connected with the covering of the ovum carried with them no decidua cells. It was hardened in alcohol, cut in series sections, and stained with hematoxylin and eosin. Examination showed a point of rupture in the wall through which the fetus had been expelled.
The important points with regard to the villi are as follows: In a well-developed villus (Fig. 31a) we find a connective-tissue centre made up of long, thin, and branching cells situated in a basis composed of a finely granular, frothy, and often red-staining substance like that found in the fetal sac. On this connective-tissue centre is a single layer of large, sharply outlined mononuclear cells forming a continuous covering of the same. This layer frequently forms groups at the tips of the villi (Fig. 31a). This layer, the so-called layer of Langhans, is composed of large round or polygonal cells with a pale, almost waterclear, protoplasm poor in granules. The nucleus is large, round, and homogeneous and generally contains one nucleolus. The layer of Langhans is separated from the stroma of the villus by a sharp outline. The side away from the mesoderm is smooth ami covered by a distinct structureless membrane. The outer syncytial covering is a thin layer of protoplasm containing a single row of dark nuclei. In the stroma of these villi may be seen round spheroidal trophoblast cells, and their change into nucleated red blood cells can be readily observed.
Fig. 316. — An outgrowth on the membrana chorii containing trophoblast cells in the lower portion, and showing the various changes to distinct Langhans cells in the centre, and especially to syncytium and syncytial masses on contact with maternal blood in the periphery.
The younger villi and the large cell groups which represent the early formative stages of villi possess the same structure and cells as the outgrowths found on the external surface of the membrana chorii (Fig. 316). "We find villi composed entirely of spheroidal trophoblast cells surrounded by a covering of syncytium. The gradual transition from these trophoblast cells into syncytium, and the change of the trophoblast nuclei into the nuclei of the syncytium, can be distinctly observed (Figs. 315 and 32). Other villi are composed of trophoblast cells with a distinct protoplasmatic body (Fig. 32a). The trophoblast nuclei preserve their pronounced spheroidal form. The syncytial covering is at numerous points possessed of more than a single layer of nuclei and sends extensions into the trophoblast centre. Other villi composed of trophoblast nuclei possess a beginning centre of mesoderm (Fig. 33). The syncytial covering contains vacuoles in the wall of which are crescent nuclei. A further stage is represented in villi whose mesodermal stroma contains but few trophoblast nuclei and where the syncytium, thin as endothelium, rests on no layer of Langhans (Fig. 34). In numerous villi, at one end is found the typical structure of a complete villus, the syncytial covering evidencing sprouts of a polynuclear character (Fig. 35). The other end of the villus is of a younger stage. The syncytium is there at the period characterized by the frothy, finely granular character of the protoplasm, while the nuclei are irregular in form and do not stain deeply (Fig. 35). Here, too, the change of trophoblast nuclei into syncytial elements is evident. In the cell groups (Fig. 35a) we observe a covering of syncytium which at numerous points extends into the substance of the cell group, forming protoplasmatic masses of a thin endothelial character or of a polynuclear nature, and which divide the cell groups into irregular fields (Fig. 35&) wherein may be recognized the various early stages of subsequent villi (Fig. 35c) . This invasion of syncytial cells is not alone an active growth, but is due to the infiltration of a cell group by blood, which transforms the cells with which it comes into contact into syncytium. Here most distinctly can the gradual transition from trophoblast to syncytium be observed. The large, polynuclear groups and knobs of syncytium, the so-called giant cells, are found at all points in the intervillous space. The nuclei are round, flat, and crescent shape. They are very frequently attached to the villi by larger or thinner pedicles. They are frequently found at the tips of the villi, where they represent the change of the small so-called cell groups, or pillars, to syncytium. The villi are, then, in their various stages simply reproductions of what is found in the membrana chorii.
Fig. 32. — Villus composed of trophoblast cells showing transitions to the syncytial covering and to syncytial groups on the left.
Fig. 32a. — Villus composed of trophoblast cells with distinct large protoplasm.
Fig. 33. — Villus with beginning centre of mesoderm. The syncytial covering contains vacuoles and crescent-shaped nuclei.
Fig. 34. — Older villus with thin syncytium and no layer of Langhans.
Fig. 35. — Villus showing an older stage in the left half and a younger stage in the right half.
Fig. 35a. — Cell group with syncytial elements invading it at various points.
Fig. 35b. — Further stage of Fig. 35a. Cell group divided by syncytial elements, with the formation of fields which represent future villi.
Fig. 35c. — A further stage of Fig. 356. Cell group divided into syncytial masses and villi. V 2 , villus in whose stroma are nucleated red blood cells ; 8j a syncytial mass ; T, syncytial nuclei resulting from changes in the trophoblast cells ; Tr., trophoblast cells with beginning change to syncytial nuclei ; V v villus with whose syncytial covering numerous bridges of syncytium are connected.
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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 19) Embryology Book - Uterine and tubal gestation (1903) 1-8. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Uterine_and_tubal_gestation_(1903)_1-8
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