View source for Paper - The early looping of the alimentary canal in the mammalian and human foetus and the mechanisms assumed to be active in this process

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=Review - The early looping of the alimentary canal in the mammalian and human foetus and the mechanisms assumed to be active in this process=

By Gustaf Enbom

Tornblad Institute of Comparative Embryology and Department of Anatomy, Lund University, Sweden


One Figure


==Introduction==

In a work on the formation of the umbilical cord and the umbilical region of the anterior abdominal Wall Wyburn (’39) also touched upon the interesting problems of the origin and reduction of the physiological umbilical hernia. His account, ho\\-‘ever, may be supplemented with the views of these important. embryodynamical processes to which I have come after extensive comparative embryological studies of man and other mammals (Enbom, ’37, 1 and 2; ’38, 2). I shall therefore brieﬂy outline in English the most important results of my earlier works as Well as of a recent Work on the development of the shape and position of the alimentary canal in mammals (Enbom, ’39). It may be premised that among‘ other innovations for these investigations a new plastic method of reconstruction has been elaborated, in which use is made of plastiline plates instead of wax plates (Enhom, ’37, 1; ’38, 1).

The part played by the vitelline artery, a. omphalomesenterica, in the retraction of physiological umbilical hernia in the opossum, Didelphys virg'iniana, was dealt with in my earlier works (’37, 1 and 2). Respecting the mechanism behind the early reduction of the umbilical hernia. in this primitive mammal it was there shown that the omphalomesenteric artery is greatly shortened in connection with the replacement of the umbilical loops. Thus it was established that the stretch of the artery in question from the aorta to the point at which it leaves the mesentery at the ﬂexurc of the primary umbilical loop (;c in ﬁg. 1) is contracted to only one-half its former length in this its mesenteric portion; that. is, the last-mentioned point (X) is drawn dorsally to a corresponding extent, and the most ventral section of the umbilical loop comes to lie within the aperture through which the hernia. protruded, in spite of the fact that the dors0—Ventra.l diameter of the abdominal cavity has not become larger (compare ﬁg. 1 a and b). At this sta;;e.—in about 1—cm.-long embry0s—the intestinal system is still in a simple phase of development; the small intestine is folded together in a characteristic manner in two groups of loops that pass arcuately around the vitelline artery. In consequence of the shortening of the vessel trunk contained in the mesentery these intestinal loops are tightly compressed, displaced in a dorsal direction and drawn into the abdominal cavity, but otherwise there is no change in their relations to the mesenteric portion of the vitelline artery, which portion forms the axis of the umbilical hernia.


[[File:Enbom1939 fig01.jpg|600px]]

'''Fig. 1a and b''' Diagrammatic side View of plastiline models of opossum embryos, (a) 9.4 mm and (b) 11.2 mm. Linear course of the intestinal canal with the omphalomesenteric artery axial in the C-onvolute system. In the older foetus the pliysiological umbilical hernia has been drawn in as a consequence of the vitelline artery having been shortened by one—half, the gastro-enterie coil in its entirety then being pressed together with dorsal tlisplacexnent. A0 = aorta together with a. omphalomesenteriea. C = coecum. S = stomach. ac = point at which vitelline artery leaves mesentery. Large intestine drawn with thicker line. 8/1.



The omphalomesenteric artery of the opossum is capable of a contraction of this kind with consequent replacement of the umbilical loops. At the time of the retraction of the extra-embryonic loops the vitelline artery is found to be equipped with a considerable longitudinal muscular apparatus. Hence the contraction of this artery can take place with the necessary power when an opportunity of shortening presents itself.


As a matter of fact this View is supported by an observation made by Rathke (1839). He found that the vitelline vessels in the commonsnake embryo shorten towards the end of foetal development. No umbilical hernia has been observed in the foetus of the common snake, but the yolk sac wanders into the abdominal cavity. Respecting the cause of this Rathke writes (l.c., p. 184): “Was die Ursache der erwéihnten Wanderung anbelangt, so liegt sie, wie ich glauben muss, in den Stammen der Dottergefasse (Vene und Arterie), die sich gegen Ende des Fruchtlebens offenbar bedeutend verkiirzen.” The omphalomesenteric vein separates from the mesentery of the umbilical loop at an early stage and cannot therefore assist in the reduction of the umbilical hernia.


Especially great importance attaches to the vitelline circulation of the opossum as well as of marsupials in general, for during their short embryonic development no allantoic placenta is found. The vitelline circulation provides for all exchange with the maternal blood through the medium of a yolk-sac placenta and therefore attains to a comparatively high degree of development. As a retracting organ, however, only that part of the vitelline artery which is contained in the umbilical-loop mesentery can come into question. Now since this sooner or later always gives rise to an important intestinal artery, in man, e.g., the a. mesenterica cranialis, it cannot be regarded as improbable that this the axial arterial trunk of the umbilical hernia may also act in other cases at an opportune moment as a muscular retracting organ in the same manner as in the opossum.


The inquiry was therefore carried further with material, as before, from Prof. Ivar Broman’s comparative embryological collections at the Tornblad Institute in Lund. And in the next work (Enbom, ’38: 2) it was possible to show in embryos of Homo as well as of Spermophilus citillus and Galeopithecus volans a condition similar to that previously demonstrated in the opossum, viz. that on retraction of the umbilical hernia the axis of the umbilical loop is deﬁnitely shortened. Just as in this lowly mammal, so in the other mammals studied here, the reduction is accompanied by a dorsal displacement and a compression of the intestinal loops corresponding to the shortening of the vitelline artery that runs axially in the mesentery supporting the umbilical loop.


At this juncture the omphalomesenteric artery is the most powerful vascular trunk in the body, and its mesenteric portion is equipped with a longitudinal muscular apparatus of unusual strength. This impressive muscle, located axially in the system of intestinal convolutions, is manifestly to be regarded as a retracting organ of the best type to fulﬁll all requirements, and one that is not only able to retract the umbilical loops but also to retain them within the abdominal cavity until the aperture in the anterior abdominal wall has had time to close.


Those cases in which the reduction takes place successively may be due to a differentiated tonicizing of the retracting muscle in the umbilical-loop mesentery, or to the resistance offered, when regression is delayed or stretching arrested, by the extra-mesenteric portion of the omphalomesenteric artery, the true a. vitellina (Broman, ’14). On the other hand, should the longitudinal muscle of the omphalomesenteric artery be imperfectly developed, its activization be insuﬂicient or arrested, a congenital umbilical hernia would be the consequence.


In the latest work (Enbom, ’39) some further rules are advanced for the early looping of the alimentary canal in the mammalian and human foetus, and a discussion of the mechanisms that can be assumed to be active in this process is carried further. By way of introduction deﬁnitions are given of various types of loops (after Pernkopf, ’25).


A basic plan is submitted of the primary looping. Four primary loops are deﬁned: the gastric, duodeno-jejunal, umbilical, and colonic. The mechanism underlying the origin of the primary umbilical loop is discussed. It is shown that at the time it comes into existence the umbilical loop is regularly surrounded by two arterial trunks, the aa. vitellinae, with the result that the umbilical loop is directed between these arteries and grows out ventrally through the umbilical aperture. The twist of this loop from a sagittal to a transverse position appears, most probably, to be attributable to the strong growth of the liver, the umbilical loop being constrained to take up a transverse position with its limbs along the caudal surface of the liver, tangent to this.


The various coiling and shifting phases undergone by the gastric loop during its development are taken up for study. On the whole it appears probable that the stomach turns about a longitudinal, a transverse, and a sagittal axis. Respecting the two last-mentioned changes in the position of the primordium of the stomach, it is stressed that during the caudal migration of the gastro-intestinal system the pyloric portion becomes ﬁxed in a position transversely across the omphalomesenteric artery.


A basic plan of the secondary looping is given. Three main groups of secondary loops arise in diiferent planes around the omphalomesenteric artery: a sagittal group of dorsal loops, intra-abdominal loops of the small intestine to the right, a transverse group of ventral loops, extra-abdominal loops of the small intestine caudally, and to the left generally only a single sagittal loop of the colon, though in some cases (eg. Spermophilus, Galeopithecus) several secondary colonic loops form a separate sagittal group on this side of the artery.


This fact, that in certain cases both limbs of the primary umbilical loop are secondarily convoluted, suggests that it must be the vitelline artery which brings about the ﬁxation of the top of the umbilical loop necessary for this convolution.


The same causes as bring the primary umbilical loop down into a transverse plane along the caudal surface of the liver, bring its extraabdominal secondary loops to development in a transverse position caudally to this plane.

==Summary==

Evidence has been submitted of the important part played by the omphalomesenteric artery in the development of the shape and position of the stomach and intestine in the mammalian and human foetus. This artery prevents the pyloric portion of the stomach from sinking caudally and therefore gives rise to characteristic changes in the position of the primordium of the stomach. It is a retractive organ for the umbilical loop, an organ that by arresting the latter ’s ventral growth ﬁrst constrains the limbs of this loop to undergo secondary convolution and subsequently, on attaining full retractive power, brings about a drawing—in of the umbilical loops with a heaping together of the gastrointestinal bundle as a whole~—a force of the most manifest importance for the development of the gastro-intestinal system. The intestinal tube Winds itself round the artery in question, forming typical groups of loops. In this way the omphalomesenteric artery comes to act as the principal axis of the intestinal bundle, and it is around this axis that the bundle turns.

==Literature Cited==

BROMAN, I. 1914 ﬁber das Schicksal der Vasa vitellina bei den Séiugetieren. Ergebn. Anat. I1. Entw.-gesch., Bd. 21 (1913), S. 99.

ENBOM, G. 1937 Gegenseitige Abhéingigkeit der Geféiss- und Organentwicklung beim Opossum nebst Studien iiber die Eutstehxmg der hinteren Hob}vene bei Bos und Vespertilio sowie Beitrtigen zur Rekonstruktionstechnik. Diss. Gleerupska Universitetsbokhandeln, Lund.

1937 ﬁber die Rolle der Dottersackarterie bei der friihen Reposition des physiologischen Nabelbruches beim Opossum. Morph. Jb., Bd. 80, S. 495. (Other literature stated here.)

1938 Ein Schnellverfahren zur Rekonstruktion in Plastilin nebst anderen technischen Beitriigen. Z. wiss. Mikr., Bd. 55, S. 150.

1938 Der Repositionsmechanismus des physiologischen N abelbruches bei Siaiugetieren und beim Menschen. Morph. Jb., Bd. 82, S. 271. 4:14 GUSTAF ENBOM

ENBOM, G. 1939 Zur Morphologie und Mechanik der Magendarmentwicklung bei Siiugern, besonders beim Menschen. Kungl. Fysiogr. Sﬁllsk. Handl., N.F., Bd. 50, 111'. 4. C. W. K. Grleerup, Lund.

PERNKOPF, E. 1925 Die Entwicklung der Form des Magendarmkanales beim Menschen. Z. Anat. u. Entvv.-gesch., Bd. 77, S. 1.

RATHKE, H. 1839 Entwickelungsgeschichte der Natter (Coluber natrix). Koenigsberg.

WYBURN, G. M. 1939 The formation of the umbilical cord and the umbilical region of the anterior abdominal wall. J. Anat. Lond., vol. 73, p. 289.

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