Paper - The development of the mucous membrane oesophagus stomach and small intestine in human embryo
Embryology - 23 Apr 2024    Expand to Translate
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Johnson FP. The development of the mucous membrane of the oesophagus, stomach and small intestine in the human embryo. (1910) Amer. J Anat., 10: 521-559.
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See also Johnson FP. The development of the rectum in the human embryo. (1914) Amer. J Anat. 16(1): 1-58.
The Development of the Mucous Membrane of the Oesophagus, Stomach And Small Intestine In the Human Embryo
Franklin P. Johnson
From the Department of Comparative Anatomy, Harvard Medical School
With Twenty-Four Figures Seven Plates
Introduction
The development of the mucous membrane of the digestive tract, although studied for many years by competent observers, still affords opportunity for further investigation. The present work was undertaken for the purpose of studying the development of the structures found in the digestive tract, and to obtain a comparable- series of wax reconstructions illustrating the changes that take place in the form of the mucosa. Especial stress has been laid on the development of vacuoles and diverticula, villi, glands, and folds. It was originally intended to include the development of the mucous membrane of the vermiform process and the large intestine, but for lack of favorable material, this has been omitted in the present paper. This work was suggested by Dr. F. T. Lewis, and has been done in connection with his chapter on the digestive tract for Keibel’s Text Book of Human Embryology. A more complete review of the literature than is here given, will be found in .)r. Lewis’ chapter.
The material used was obtained from human embryos in the Harvard Collection; The earlier stages were already prepared in the embryological collection.
The crown rump lengths and series numbers of these are as follows:
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The crown-rump lengths and numbers of the older embryos used are as follows:
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From the older embryos, the different parts of the digestive tract were separately removed, imbedded in paraffin, and cut in serial sections of 8 microns in thickness. The sections were stained by different methods, among which were Heidenhain’s iron haematoxylin, Hansen’s iron haemotoxylin, and Mallory’s aniline blue connective tissue stain. Both eosin and orange G were used as counter stains. From the preparations thus made, certain stages of development were selected, and a number of Wax reconstructions made. The models have in most cases been made to the magnification of 145 diameters, so as to be easily compared. However, in some of the gland models, this magnification was doubled, and in others trebled.
Oesophagus
Early Stages. In an embryo of 7.5 mm., the oesophagus is a cylindrical tube of epithelium extending from the pharynx to the stomach. The lumen is round and relatively large at its upper end, but tapers gradually until at its middle it is quite small. Passing downward from this region, the oesophagus gradually increases in size and at its lower end leads into the stomach, there
Mucous Membrane in the Human Embryo. 523
being no sharp line of demarcationd between the two. The indistinctness of the cell boundaries makes it very difficult to determine definitely the number of cell layers in the epithelium. Because of this, different observers have not agreed upon the number of cell layers present in the early stages. It can, however, be said with reasonable certainty that the epithelium at 7.5 mm. is stratified and in the upper and lower thirds of the oesophagus shows three or four rows of nuclei, in the middle third, two or three rows. The basal cells are the more columnar "and are characterized by having their nuclei in that end of the cell which is toward the lumen. Surrounding this central tube of epithelium is mesenchyma, which although undifferentiated is slightly condensed.
In an embryo of 16 mm. the oesophagus has increased in length and breadth. The upper end is both larger and more irregular in outline. The epithelium contains three or four rows of nuclei and lies on a very distinct basement membrane. Here again, the basal layer of cells is the more columnar and its rounded nuclei lie in the upper ends of the cells, that is, away from the basement membrane. In its lower portion, the oesophagus is smaller and oval in cross section. Throughout its entire extent the oesophageal epithelium is surrounded by mesenchyma which is limited externally by a narrow ring of deeply staining myoblasts, elongated in form, and so placed as to form the circular layer of the muscuaris.
Vacuoles. The next stage examined was an embryo of 19 mm. (series 819). In this only about the lower half of the oesophagus was available for study. The epithelial tube is now irregular in outline, and presents within its walls numerous small cavities or vacuoles. Some of these are minute, others have a diameter 0.051 mm., which is greater than the diameter of the lumen itself, making it difficult to determine from cross sections which is lumen and which vacuole. In some places the vacuoles open directly into the lumen, in other places they are separated from it by a partition of epithelium. fig. 1a is of a model of the oesophageal epithelium at this stage and shows its vacuolated structure. The portion of the oesophagus modelled was selected at a place just below the bifurcation of the trachea. In a second embryo 524 Franklin P. Johnson.
of 19 mm. (series 829) similar vacuoles are found, but are less numerous than in the above embryo of the same length. They are also more numerous in the lower portion of the oesophagus than in the upper.
At 22.8 mm. (series 871) the diameter of the oesophagus is nearly double that at 19 mm. The vacuoles are more numerous and,-as shown_in fig. lb, communicate with one another and with the main lumen to a greater extent. In the upper part of the figure the oesophagus appears to have a double lumen. This appearance is due to the fusion of a number of vacuoles. The vacuoles are about the same size as those found in the preceding embryo but the lumen has increased in diameter. Although vacuoles also occur in the dorsal and ventral walls of the oesophagus, they are less numerous there than in the lateral walls. The few vacuoles found in the dorsal and ventral walls do not show in the figures ; they are, however, of the same general character as thoseldescribed.
In other embryos of 22 mm., 22.8 mm. (series 737) and 23 mm. the vacuoles are found to be less numerous in the upper half of the oesophagus than in the lower half. At 29 mm. and 30 mm. they have become very few; at 32 mm. only slight traces of them are found; at 37 mm. they have entirely disappeared.’
Vacuoles of the nature described were noted by Schultz in 1897. Kreuter C05) believed that they cause a temporary occlusion of the oesophagus, but Forssner (’07) showed by means of models that the main lumen is not obliterated. Schridde (’08) failed to find an occlusion at any stage and denied the presence of vacuoles but described epithelial bridges which arise by epithelial proliferation in circumscribed places. From a study of these structures by means of wax reconstructions, the writer is able to confirm the results of Forssner inasmuch as the lumen is not entirely occluded and vacuoles are present.
The exact cause and significance of the vacuoles are difficult to determine. Similar vacuoles are found in the oesophagus of pig, rat and rabbit embryos. They have been reported by Forssner in the hedgehog, where in a certain stage they lead to a complete occlusion. Vacuoles similar to those of the oesophagus are found in the walls of the stomach and the duodenum of human embryos.
Kreuter states that there is no reason to believe that the vacuoles are areas of degeneration for he was nowhere able to demonstrate evidences of a degeneration of cells followed by resorption. There can be seen, nevertheless, a few nuclei lying within certain vacuoles which stain less intensely and are more indistinct than the nuclei of the epithelium. It does not appear, however, that these occasional degenerating nuclei are responsible for the production of the vacuoles. It seems obvious from the arrangement and crowded condition of the surrounding nuclei that the vacuoles increase in size. As they become larger the epithelium between the vacuoles and the lumen, and between adjacent vacuoles becomes reduced to a thin partition. This "partition eventually breaks through and makes the cavity of the vacuole and the lumen continuous.
Measurements of the thickness of the epithelial wall of the oesophagus are interesting in connection with the vacuoles. At a time when vacuoles begin to form, the epithelial wall of the oesophagus is composed of apparently three or four layers of low columnar cells. While vacuoles are present the number of cell layers varies from one to four. By a breaking through of the vacuoles into the lumen and a disappearance (or migration) of the more superficial cells, the epithelium is reduced in thickness. At 19 mm. and 22.8 mm. the epithelium averages .051 mm. while at 30 mm. only .030 mm. in thickness. This loss in thickness is soon compensated by a growth in the height of the individual cells, for at 42 mm. there are only two layers of cells, the average thickness of the epithelium being .043 mm. Two results of vacuolation are, therefore, a destruction of the more superficial layers of cells, and an increase in the size of the lumen of the oesophagus. This increase in the size of the lumen is proportionately great in the early stages but less in the‘ older ones.
Folds. At an early stage the epithelium of the oesophagus becomes thrown into large longitudinal folds which are usually four in number. Later smaller folds develop at the bases of , or in between, the larger ones. These folds give to the oesophagus in cross section the appearance of a Maltese cross as was first noted by Koelliker (’61). Certain of the folds make their appearance before others and show different stages of development in different regions of the same oesophagus. The exact time and order of the appearance of these structures was studied in a number of embryos with the following results.
As stated before, the epithelial tube of the oesophagus at 7.5 mm. is cylindrical in shape, very small at its mid-region, but gradually becoming larger when followed either up or down. In embryos of 10 mm. and 16 mm. the upper portion of the oesophagus is flattened Ventro—dorsally, the middle region is circular but now more expanded, and the lower portion is flattened laterally. In the upper part of the oesophagus there is a slight infoldof the ventral wall of the epithelial tube.
In the upper part of the oesophagus at 22.8 mm. (series 871) there is a Ventral infolding of the epithelium. This is the direct downward continuation of that fold of the pharynx which gives to the latter, when seen in cross section, its characteristic crescentic shape. Following downward this fold is soon lost and the oesophagus becomes rounded. Another fold appears in the mid region of oesophagus, this being an infolding from the dorsal side. Still further caudally, as the stomach is neared, a third infolding is found, this being left lateral in position. This lateral fold in an older embryo is seen to be directly continuous with the dorsal fold above. The folds found in this embryo are, therefore, really two in number, a ventral one which appears in the upper third of the oesophagus, and a dorsal one which is seen in the middle third and again as a lateral fold in the lower third. Since the study of the order of the appearance of these folds was made by wax reconstructions in a series of embryos, it was necessary to secure for modelling approximately the same level of the oesophagus in each specimen. The region selected was that immediately below the bifurcation of the trachea.
The oesophagus at 37 mm. in the region of the bifurcation of the trachea (fig. 2) is somewhat crescentic in cross section. Dorsally, facing the dorsal aorta, there is a deep fold which continues upward and downward and passes directly onto the stomach. In the lower third, however, it deepens and ‘changes its position by moving through an arc of about 90° to the right. At 42 mm. in the same region as the above (fig. 3) there are two distinct folds, a dorsal and a ventral. These folds, which I have designated as the first pair of primary folds, are continued downwards onto the stomach, but before reaching it are twisted to the right and occupy positions on the‘ left and right sides of the oesophagus respectively. In the figure a second pair of primary folds can be seen, which, although indistinct at this level, are well marked below. In the region modelled and below it, the fold on the left side is the more marked, but above the right fold alone is seen, and the ventral and dorsal folds approach one another on the left side, making a three sided figure. At the extreme upper end of the oesophagus these folds become irregular and are broken up by the formation of other smaller folds. All the folds shown in fig. 2 are twisted as the stomach is neared, each occupying a position of-about 90° to the right of its original position.
At 55 mm., both pairs of primary folds are well developed (fig. 4) and give to the lumen of the oesophagus in cross section the appearance of a Greek cross. These folds are also seen in embryos of 30 mm. and 42 mm. in the lower parts of the oesophagus. As seen in fig. 5, at 134 mm., these primary folds are augmented by secondary folds which develop at the bases of the former. Three such folds are seen in fig. 4,, one of which is quite large. The same folds are found in embryos of 187 mm., 240 mm., and at birth.
By way of summary concerning the development of folds of the mucous membrane of the oesophagus, it may be said that the dorsal one is the first to develop completely. This is followed closely by the ventral fold. The second pair of prima ry folds develop from below upwards and have reached to the bifurcation of the trachea in an embryo of 42 mm. The secondary folds are less constant structures. They begin as thickenings of the epithelium between the bases of adjacent primary folds. In the upper part of the oesophagus, especially in the older stages, folds are very irregular. The reader is referred to Table 1, page 532 for measurements of folds of the oesophagus in different stages of development.
The fact that the epithelial folds of the oesophagus rotate through an angle of about 90 degrees and always in the direction of the hands of a clock, seems to have some significance. Just what the cause of this rotation may be is debatable. Kreuter discards the idea that the lower part of the oesophagus may share in the rotation of the stomach. However, this may be its cause. This view is supported by the arrangement of the branches of the Vagus nerves. These branches are also twisted at. the same level as the oesophageal folds. It would, therefore, not seem improbable that the lower part of the oesophagus had been twisted along with the nerves by the stomach. Since the twisting of the stomach takes place before the appearance of the folds, it would necessarily have to be assumed that the lines along which the first oesophageal folds develop are marked out before the actual. appearance of the folds themselves.
Ciliated cells. The presence of ciliated cells in the oesophagus was noted in 1876 by Neumann, who observed them in embryos of from 18 to 32 weeks. He described the epithelium as stratified, the superficial layer being made up of patches of both ciliated columnar and squamous cells. Schaffer (’04), confirmed by Jahrmaerker (’06) and Schridde (’07), states that the ciliated cells may extend through the thickness of the epithelium down to the basement membrane. Jahrmaerker has recorded the presence of ciliated cells. in the oesophagus of an embryo at 4.4 mm. In an embryo of 42 mm. no ciliated cells could be found, but the preservation of this embryo was poor and the staining unfavorable for the recognition of cilia. In a specimen of 55 mm. ciliated cells are abundant. Here the epithelium of the oesophagus is composed of from two to four layers of cells with distinct cell boundaries. The basal cells are columnar and have their oval nuclei away from the basement membrane. In those places where there are not more than two layers of cells, the superficial cells are columnar, very granular, and ciliated. Where there are three or four layers of cells, only the lower layer is columnar, the upper layers being composed of polygonal or flat cells.
In order to study the distribution and number of - the ciliated cells, wax reconstructions were made, the areas of ciliated cells being carefully painted on each wax section before piling. fig. 6, from an embryo of 55 mm., shows one half of a model viewed from its inner surface. The stippled areas represent those covered with cilia. As can be seen, the larger areas of ciliated cells are on the folds and these areas include but few islands of polygonal cells. Between the folds there is a preponderance of squamous cells, which are interrupted by a few small ciliated patches. In the upper part of the oesophagus the ciliated areas are slightly larger than in the region modelled. A similar reconstruction was made of the epithelium of the oesophagus at 99 mm. (fig. 7). It shows that the amount of ciliated surface has actually and relatively increased and there are now more islands of polygonal cells on the folds.
In embryos of 120 mm., 134 mm., and 187 mm., ciliated cells in the oesophagus are observed to be distributed in about the same proportions as at 99 mm. At eight months the upper part of the oesophagus shows only a few small patches of ciliated cells. In a specimen at birth the areas are abundant but proportionately smaller than in the earlier stages, and the islands are now more widely separated. The islands consist of distorted columnar ciliated cells, the distortion probably being due to the pressure of the rapidly increasing polygonal cells, which are seen crowded closely against the islands and in places partly undermining them. In a child of two weeks (7 months premature birth) no ciliated cells can be found in any part of the oesophagus. Jahrmaerker and Schridde were unable to find ciliated cells at birth.
Glands. In regard to the glands of the oesophagus, there are two distinct types to be considered; the true or deep oesophageal glands, and the cardiac or superficial oesophageal glands. The former are found in the adult all along the oesophagus, with the exception of the lower 2 to 4 mm. of its length; the latter in the lower 2 to 4 mm. and also (70 per cent of cases examined by Schaffer) in that portion of the upper part of the oesophagus which lies between the level of the cricoid cartilage and the 11th tracheal ring.
In an embryo of 78 mm. (incomplete series 723 and 724) small patches or islands of glandular epithelium are found in both the upper and lower ends of the oesophagus. Schaffer (’04) described similar groups of cells in an embryo of four months, at the level of the third or fourth tracheal cartilage, and Schrid'de (’07) found a group in an embryo of 105-110 mm. (16 to 17 weeks) at the level of the cricoid cartilage. Areas of glandular cells are abundant in the lower part of the oesophagus at 120 mm. Some groups are arranged as islands, others are evaginated so as to form small pockets. From the bottoms of these pockets budding glands are seen. In the lower part of the oesophagus at 240 mm. the glandular cells are more conspicuous. On the sides of the large folds, but chiefly at their bases, patches of secreting cells are seen forming small isolated islands, pockets, and grooves. The glandular epithelium is high columnar and is everywhere surrounded by stratified squamous and ciliated cells. The pockets form the ampullze of the cardiac glands, from which numerous small buds have grown out. A model of such a gland, found at the bottom of a fold at the lower end of the oesophagus, is shown in fig. 8. The surface which is ruled in the figure indicates the simple glandular epithelium; the unruled surface, the stratified squamous epithelium.
The presence of the deep oesophageal glands was first noted in an embryo of 240 mm. Their beginnings are seen as small outgrowths of the stratified epithelium. These buds are found at the bases of the primary folds and upon the outer surface of the secondary folds. They are lined by a stratified squamous epithelium similar to that lining the oesophagus. In a specimen from the upper part of the oesophagus at 8 months, a gland was found which extended through the muscularis mucosae into the submucosa. Its walls were composed of one and two layers of cuboidal cells, but nowhere throughout its entire extent could secreting cells be seen.
At birth the oesophageal glands (fig. 9) have grown out through the muscularis mucosae and lie in the inner part of the submucosa. The mouths of the glands are lined with a stratified squamous epithelium of three or four layers of cells which is directly continuous with the oesophageal epithelium. Gradually the stratified squamous epithelium passes into the double layer (in some places single), of low cuboidal cells which lines the excretory duct. The excretory duct of the gland passes through the thick muscularis Inuscosae at nearly right angles to the surface epithelium. On reaching the outer border of the muscularis mucosae, it bends to either side. Instead of pointing toward the stomach, as has been described in. the adult oesophagus (Goetsch), glands may extend either upward or downward. The distal terminations of most of the glands are expanded and lined by a simple glandular epithelium of low columnar cells. In the gland A (fig. 9) the end piece shows a number of bud—like processes which are the beginnings of branches. The end piece of gland B is a simple curved expanded tube, the expanded portion being for the most part glandular. In the gland C there is no end piece at all, the whole gland being lined by two layers of non—secreting low cuboidal cells. In a study of the oesophageal glands of the pig, Flint has described a similar early stage, in which the glands contain no secreting cells. However, glands of this type are rather rare in the human embryo at birth, there being a preponderance of those with secreting cells and beginning branches.
In summarizing the development of glands of the oesophagus, it may be said that the first evidence of the cardiac glands is the appearance of small patches of glandular cells in the surface epithelium. These patches occur at both the upper and lower ends of the oesophagus and are seen as early as the third month. Later, by evagination, small pockets are formed from these patches. This is followed by a subsequent budding from the outer surface. Thus are formed a number of branches which open into a single pocket or ampulla. Cardiac glands never extend through the muscularis mucosae. The deep oesophageal glands, first seen in an embryo of 240 mm., are outgrowths of the stratified squamous epithelium, which after piercing the muscularis mucosae, bend to either side, and lie in the submucosa close to the muscularis mucosae. The secreting cells do not appear until after the gland is well formed, and are found only near its distal termination. Here at birth a number of budding processes, lined with a secretory epithelium, are seen arising from the end pieces. Thus the cardiac glands and the oesophageal glands differ in that, in case of the cardiac glands the secretory epithelium appears before the
Cite this page: Hill, M.A. (2024, April 23) Embryology Paper - The development of the mucous membrane oesophagus stomach and small intestine in human embryo. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_The_development_of_the_mucous_membrane_oesophagus_stomach_and_small_intestine_in_human_embryo
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