Paper - A contribution to the development of the duodenum
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A Contribution to the Development of the Duodenum
BY R. H. Hunter, M.D., M.CH.
Lecturer in Anatomy, Queen’s University, Belfast
The development of the adult digestive tract from a simple tubular structure is the result of a series of growth changes which take place in different regions of the primitive gut. These changes are at first mainly in the direction of increasing the length of the gut tube without any marked change in its diameter. Four regions are recognised where axial growth proceeds rapidly. In the first region — the oesophageal — the gut growth and the growth of the cervical and the thoracic regions of the body proceed at approximately the same rate. In the other regions, i.e. from the cardiac end of the stomach to the junction of the gut with the proctodaeum, the gut increases much more rapidly in length than the abdominal cavity, hence loops of gut are formed which have been described by Bardeen (1 ) as
(a) The gastro-duodenal.
(b) The entero-colic.
(c) The colic loops.
The first loop he describes as giving rise to the adult stomach and the upper part of the duodenum. The second gives rise to the remainder of the duodenum, all the small intestine and the large bowel as far as the middle of the transverse colon. The third loop develops into the remainder of the large intestine.
Robinson (2) recognises three factors which come into play in determining the final position of the adult gut tube:
(a) The growth changes in the gut itself.
(b) The growth of neighbouring organs.
(c) The method of attachment of the mesodermic mesentery and the length of this mesentery which determine the amount of free movement of the part of the gut to which it is attached.
The view of Bardeen(1) that the duodenum is developed from the adjacent ends of the first and second loops is not taken by Frazer and Robbins (3), who hold that the duodenum is not developed in this manner, but that a segment of the primitive gut tube between the ends of the first and second loops remains unchanged during the formation of the three primary loops. This segment at a later period develops into the duodenal loop.
In a subsequent paper Frazer (4) gave as his opinion that the segment between the two upper primary intestinal loops was “ elongated in accordance with and was curved out by the growth of the head of the pancreas ” to form the adult duodenum.
Buta consideration of the following facts shows that the growth of the head of the pancreas cannot be the sole factor producing the loop of the duodenum:
(a) Numerous cases are on record of adult human subjects in whom a duodenal loop is described as being present, hanging from the dorsal abdominal wall, by a mesentery, the head of the pancreas not,being contained within the loop, but lying behind or to the side of the gut (Reid (5), Papez (6), Bryce (7), Eddy (8), Clermont (9)).
(b) Again, if Frazer’s view be strictly correct, one would not expect to find a curved duodenum in animals which do not possess a part of the pancreas in the form of a distinct “ head ” as it is found in the human organ. In a number of animals, however, in which such a “head” is absent, the duodenum still forms a distinct loop. In an article by Carner(1o), figuring a number of specimens of the injected pancreas in the developing pig, a distinct duodenal loop appears to be the normal condition, yet the pancreas of this animal bears nothing in the nature of a “head” which would cause the loop. Sisson (11) describes this pancreas as being triangular in form. In the horse the duodenum forms a distinct loop, suspended from the dorsal abdominal wall by a mesentery, but the shape and position of the pancreas are such that it cannot have caused the duodenal loop. In the ox and in the sheep, in each of which there is a large complex stomach and a relatively small though distinct duodenal loop, the pancreas is so irregular in form that it appears impossible that it should have any influence in the shaping of the gut. In the cat and in the dog the form of the duodenum strongly resembles the form in man, yet the pancreas consists of two long narrow limbs, one limb passing across the dorsal wall of the abdomen, the other limb following the curve of the intestinal wall, and lying within the folds of the mesoduodenum. It appears improbable that such a slender band could be the sole factor in producing the curve of the duodenum.
(c) Further, in the human embryo at a period when the duodenal loop is well developed, the pancreas is a relatively unformed structure, lying more or less diffusely in the mesentery. This is clearly demonstrated by an examination of the wax-plate reconstruction of a 22 mm. human embryo (fig. 5) and the horizontal section of the same embryo through the duodenum, dorsal mesentery and pancreas (fig. 2).
The above evidence seems to make it clear that some inﬂuence or inﬂuences other than the growth of the “ head ” of the pancreas must be at work to produce the curve of the duodenum, as in each ‘case the pancreas bears a different relation to the duodenal loop.
fig. 1. H.S. through the duodenum of a. 6mm. human embryo, showing the bile duct on the postero-lateral aspect of the gut.
fig. 2. H.S. through the duodenum and dorsal mesentery of a 22 mm. human embryo, showing the bile duct on the postero-medial aspect of the gut.
fig. 3. Wax-plate reconstruction of the duodenal’ region of a 6mm. human embryo. This reconstruction demonstrates the small segment of gut between the gastro-duodenal and the entero-colic loops of Bardeen from which is developed the major portionﬂof the duodenal loop. The lower part of the liver has been removed, and the reconstruction viewed from the right side.
The wax-plate reconstruction of a 6 mm. human embryo is shown in fig. 3. In it a short length of intestine is seen between the primary gastric and enterocolic loops. It is attached to the dorsal abdominal wall by a thickened part of the mesentery. The upper limit of this part of the mesentery (the mesoduodenum) is just below the opening of the bursa omentalis (the foramen of Winslow of the adult), of which it forms the lower boundary, while its lower limit is marked off from the remainder of the mesentery by a small recess, which is thus situated between the rounded lower border of the mesoduodenum and the mesentery of the entero-colic loop. It is from this short length of the gut that the second, third and fourth parts of the duodenum are developed. To demonstrate the changes in the form of the developing duodenum, waxplate reconstructions of this part of the gut were made from 13, 22 and 30 mm. human embryos. In the 13 mm. stage the duodenal gut appears to be fixed at the upper and lower attachments of the mesoduodenum, by what may be termed “fixation bands.” The upper of the “fixation bands” is beyond the pylorus. It is formed by a condensation of mesenchyme which extends from the tissue of the septum transversum round the right gastric bloodvessels to the junction of the duodenum with the pylorus. The lower “ fixation band” is formed by a condensation of the mesenchyme round the superior mesenteric artery. It corresponds in position to the muscle of Treitz. Frazer and Robbins (12) are unable to discover “undoubted evidence” of the presence of this muscle before the 35 mm. stage, that is, at a period when the duodenal form is practically completed. They state, however, that the method employed in staining their preparations may make more difficult the recognition of the band before this time. In the series of embryos available in Belfast University a distinct condensation of mesenchyme can be seen around the right gastric and superior mesenteric blood-vessels in the 22 mm. stage and a condensation can even be seen in the 13 mm. stage. It is at this latter stage that the first indication of the looping of the duodenum occurs. The synchronous appearance of these two bands of tissue and the beginning of the looping of the duodenum suggest that in some way the form of the gut is inﬂuenced by, if not dependent on, their presence, that they fix the proximal and distal ends of the duodenum and prevent it taking part in the entero-colic loop.
From the pyloric end of the stomach to the upper fixation band there is a segment of small intestine which develops into the first part of the duodenum in the adult. This segment always has a distinct mesentery even in the adult. It is the terminal part of the gastro-duodenal loop of Bardeen. Hence the stages in its development are closely connected with the growth changes in the stomach and are only partly related to the development of that part of the duodenum which is attached to the posterior abdominal wall between the upper and lower fixation bands described above.
Between the 6 mm. stage and the 13 mm. stage the whole of the gut grows considerably in length and this lengthening affects the duodenum between the fixation bands in such a way as to produce looping of this portion. The growth commences from the cranial end and a loop is produced in a sagittal plane convex forwards. The lower half of the duodenal segment then commences to grow in length, but owing to the shortness of the mesoduodenum and the presence of the large mesentery of the entero-colic loop with the rapidly growing upper limb of this loop, it is forced to grow laterally to form another distinct loop in a coronal plane and with its convexity directed caudally and to the right. In the 13 mm. stage this double looping of the duodenum is to be seen (fig. 4). With the continued rotation of the stomach to bring the original Ventral or anti-mesenteric border into a horizontal plane, the upper loop of the duodenum is forced to rotate in the same direction, and hence this original Ventral loop tends to be twisted to the right so that the original right side of the mesentery now lies more and more in a coronal plane and the whole loop becomes a single loop concave to the left. The rotation is well shown in the altering position of the opening of the common bile duct which changes from a dorso-lateral position‘ to a dorso-medial position (figs. 1 and 2). In the 22 mm. embryo the upper part of the loop is seen to have rotated slightly and the whole of the duodenum is now lying to the right of the middle line. As this axial rotation continues the anti-mesenteric border of the duodenum lies enti-rely in a coronal plane and the whole of the loop is in contact with the posterior abdominal wall.
fig. 4. Wax-plate reconstruction of the duodenum of a 13 mm. human embryo, showing the second stage in the development of the loop. The reconstruction is viewed from the ventral surface of the embryo.
fig. 5. Wax-plate reconstruction of the duodenum of a .22 mm. human embryo, showing the third stage in the development of the loop. The reconstruction is viewed from the ventral surface of the embryo.
fig. 6. Diagram of the stomach, duodenum and colon of a 44 mm. human foetus, showing the final stage in the development of the duodenal loop. (From a reconstruction.)
About the 40mm. stage the extra-abdominal gut becomes included within the limits of the abdominal cavity and a further change takes place in the duodenal region. The caecum and the remainder of the large gut on their entry into the abdomen occupy a position directly under the anterior edge of the liver. Gradually, owing to the rapid growth of the small intestine and of the whole abdominal cavity and a relative shortening of the mesocolon, the large gut migrates more and more posteriorly until it occupies a position along the posterior abdominal wall. As the colon comes into contact with the loop it completes the folding backwards of the duodenum against the dorsal wall of the abdomen, and also adheres to the duodenum at the point of crossing (fig. 6). The mesoduodenum up to this stage is complete, but soon, however, the gut takes up its adult retro-peritoneal position by the disappearance of the mesothelial cells of the parietal peritoneum and those of the dorsal or right layer of the mesoduodenum.
1. The duodenum, from the developmental point of view, is not simply a part of the small intestine, but is developed separately and is liable to variation without involving other parts of the intestine.
2. The duodenum owes its adult position to three factors acting on the developing gut segment:
(a) A series of differential growth changes which lead to the formation of two loops in the primitive straight duodenum.
(b) The position of these loops governed by changes which take place in neighbouring organs and which force the tube to take ‘the form shown in the various stages. ‘
(c) The disappearance of the mesentery after the colon and the duodenum have assumed their adult relations to the posterior abdominal wall. The duodenum and the colon adhere together by a fusion of their peritoneal coats at the point where they cross.
3. The pancreas, far from inﬂuencing the form of the duodenal loop, seems to grow along the planes of least resistance and to be moulded by the neighbouring organs rather than mould them.
In conclusion I wish to thank Professor Walmsley for his valuable advice in the preparation of this article.
(1) Bardeen CR. The critical period in the development of the intestines. (1914) Amer. J Anat. 16: 427 – 445.
(2) ROBINSON, BYRON. Journ. Anat. and Physiol. vol. XXXIII, p. 438.
(3) FRAZER, J. E. and ROBBINS, R. H. Journ. Anat. and Phystol. vol. I, p. 75.
(4) FRAZER, J. E. Joum. Anat. and Physiol. vol. LIII, p. 202.
(5) REID, D. G. Journ. Anat. and Phystol. vol. XXXII, p. 320.
(6) PAPEZ, J. W. Anat. Rec. vol. XXI, p. 309.
(7) BRYCE, T. H. Joum. Anat. and Phystol. vol. XXXIII, p. 27.
(8) EDDY, N. B. Anat. Rec. vol. VI, p. 319.
(9) CLERMONT, M. Bull. Soc. Anat. Paris, T. LXXX, p. 884.
(10) CARNER, G. W. Amer. Journ. Anat. vol. XVI, p. 207.
(ll) SIssoN, SEPTIMUS. Anatomy of the Domestic Animals, 2nd ed., p. 207.
(12) FRAZER, J. E. and ROBBINS, R. H. Joum. Anat. and Physiol. vol. L, p. 81.
Cite this page: Hill, M.A. (2020, October 31) Embryology Paper - A contribution to the development of the duodenum. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_A_contribution_to_the_development_of_the_duodenum
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