Morphogenesis and three-dimensional movement of the stomach during the human embryonic period

Changing the topographical anatomy among the maxilla, palatine bone, and greater palatine nerve: a histological study using human fetuses

PURPOSE

The palatine bone (PAL) rides over the maxilla (MX) without an end-to-end suture in the bony palate of fetuses. However, changes in the topographical relationship among bones was unknown at and along the pterygopalatomaxillary suture, including the palatine canals.

METHODS

Using sagittal, frontal, and horizontal histological sections of the head from 15 midterm fetuses to 12 near-term fetuses, we depicted the changes in the topographical anatomy of the MX, PAL, and greater palatine nerve (GPN).

RESULTS

In the bony greater palatine canal of these fetuses, the medial and posterior walls facing the GPN were consistently made up of the PAL. At midterm, the entire course of the GPN was embedded in the PAL (six fetuses), or the MX contributed to the lateral wall of the nerve canal (nine). At near-term, the anterior and lateral walls showed individual variations: an MX in the anterior and lateral walls (three fetuses), an anterior MX and a lateral PAL (five), an anterior PAL and a lateral MX (two), and a PAL surrounding the GPN (four).

CONCLUSION

These increasing variations suggested that the pterygopalatomaxillary suture was actually growing and that the PAL transiently expanded anteriorly and/or laterally to push the MX in fetuses. The "usual" morphology in which the GPN is sandwiched by the MX and PAL is likely established after birth, possibly during adolescence. The driving force of this change may not be produced by the masticatory apparatus. Rather, it might be triggered by the growing maxillary sinus.

The twists and turns of left-right asymmetric gut morphogenesis

Many organs develop left-right asymmetric shapes and positions that are crucial for normal function. Indeed, anomalous laterality is associated with multiple severe birth defects. Although the events that initially orient the left-right body axis are beginning to be understood, the mechanisms that shape the asymmetries of individual organs remain less clear. Here, we summarize new evidence challenging century-old ideas about the development of stomach and intestine laterality. We compare classical and contemporary models of asymmetric gut morphogenesis and highlight key unanswered questions for future investigation.

Topographical anatomy of the greater omentum and transverse mesocolon: a study using human fetuses

The greater omentum covers the transverse colon from the anterior side in adults, but people might believe the morphology stable once established during fetal life. Sections from 49 midterm and 17 late-stage human fetuses, of gestational ages (GA) 8–15 and 30–38 weeks, respectively, showed complete fusion between the greater omentum and transverse mesocolon after physiological herniation at GA 8–9 weeks; the transverse colon attaching to the anterior aspect of the gastric antrum and pylorus at GA 10–15 weeks; the colon pushing the pylorus or superior portion of the duodenum upward (at GA 10–15 weeks and 30–38 weeks); and the greater omentum without covering the greater portion of the jejunum and ileum but shifted leftward (at GA 30–38 weeks). These subsequent topographical variations of the transverse colon with the stomach and duodenum included the colon tightly fusing with the stomach by a fibrous tissue and; the greater omentum and/or the mesocolon wedged between the stomach and transverse colon. Therefore, in combination, the colon was partly separated from the greater omentum. Moreover, at GA 30–38 weeks, the duodenum consistently showed a horizontal loop in contrast to the usual C-loop in the frontal plane. Consequently, after a complete fusion occurred once between the greater omentum and transverse mesocolon, the topographical change of the upper abdominal viscera seemed to modify, change or even break the initial fusion of the peritoneum. A logical lamination of the peritoneum seemed not to simply connect with the surgical application.

Vermiform Appendix During the Repackaging Process from Umbilical Herniation to Fixation onto the Right Posterior Abdomen: A Study of Human Fetal Horizontal Sections

The anatomical position of the vermiform appendix varies among adults, and these variations are responsible for differences in the symptoms of appendicitis. However, to date no study has examined how and when these variations occur during fetal development. The present study examined horizontal sections of 27 midterm fetuses (crown rump length [CRL] 38-97 mm, gestational age approximately 8-15 weeks). There were 10 fetuses (CRL 56 mm or more) in which the cecum and appendix were in a posterosuperior site near the right kidney (postmigration phase), and 12 fetuses (CRL 39-72 mm) in which the ileocecal junction and appendix remained on the visceral surface of the liver in the anterior or anterolateral abdominal cavity (migration phase, after physiological umbilical herniation). Analysis of the 12 fetuses in the migration phase indicated that the appendix extended inferiorly in eight fetuses and superiorly in four fetuses. Likewise, a "preileal" appendix (a morphology in which the distal part of the appendix was in front of the terminal ileum) was present in eight of these fetuses. Extension of the appendix superiorly or inferiorly during the migration phase seems unrelated to the topographical relationship of the appendix with the terminal ileum at the postmigration phase in fetuses and in adults. Conversely, it seems likely that a retroileal appendix leads to a coiled appendix behind the ileocecal junction. "Guidance" by the liver surface seemed to be important for posterior migration, which ended with the ascent of the liver. Clin. Anat., 33:667-677, 2020. © 2019 Wiley Periodicals, Inc.

The development of the dorsal mesentery in human embryos and fetuses

The vertebrate intestine has a continuous dorsal mesentery between pharynx and anus that facilitates intestinal mobility. Based on width and fate the dorsal mesentery can be subdivided into that of the caudal foregut, midgut, and hindgut. The dorsal mesentery of stomach and duodenum is wide and topographically complex due to strong and asymmetric growth of the stomach. The associated formation of the lesser sac partitions the dorsal mesentery into the right-sided "caval fold" that serves as conduit for the inferior caval vein and the left-sided mesogastrium. The thin dorsal mesentery of the midgut originates between the base of the superior and inferior mesenteric arteries, and follows the transient increase in intestinal growth that results in small-intestinal looping, intestinal herniation and, subsequently, return. The following fixation of a large portion of the abdominal dorsal mesentery to the dorsal peritoneal wall by adhesion and fusion is only seen in primates and is often incomplete. Adhesion and fusion of mesothelial surfaces in the lesser pelvis results in the formation of the "mesorectum". Whether Toldt's and Denonvilliers' "fasciae of fusion" identify the location of the original mesothelial surfaces or, alternatively, represent the effects of postnatal wear and tear due to intestinal motility and intra-abdominal pressure changes, remains to be shown. "Malrotations" are characterized by growth defects of the intestinal loops with an ischemic origin and a narrow mesenteric root due to insufficient adhesion and fusion.

Magnetic Resonance Microscopy of Chemically Fixed Human Embryos Performed in University of Tsukuba Since 1999 to 2015

Magnetic resonance (MR) microscopy of chemically fixed human embryos performed in University of Tsukuba since 1999 to 2015 was reviewed. More than 1,000 chemically fixed human embryos stored in the Congenital Anomaly Research Center of Kyoto University were used throughout the MR microscopy project, which was divided into three terms. In the first term (1999-2005), 3D MR images of 1,204 embryo specimens were acquired with 128 × 128 × 256 voxels by a super-parallel MR microscope using a 2.35 T horizontal-bore superconducting magnet. In the second term (2005-2006), 3D MR images of seven embryo specimens were acquired with 256 × 256 × 512 voxels by an MR microscope using a 9.4 T vertical wide-bore superconducting magnet. In the third term (2013-2015), 3D MR images of a Carnegie Stage (CS) 21 specimen were acquired with 512 × 512 × 1024 voxels by an MR microscope using a 4.7 T vertical wide-bore superconducting magnet and nuclear magnetic resonance parameters of a CS23 specimen were measured with 128 × 128 × 256-256 × 256 × 512 voxels by an MR microscope using a 9.4 T vertical narrow-bore superconducting magnet. Based on the results obtained in this project, the author has proposed the future MR microscopy project in which a number of embryo specimens will be imaged with 256 × 256 × 512-512 × 512 × 1024 voxels using a newly designed super-parallel MR microscope. Anat Rec, 301:987-997, 2018. © 2018 Wiley Periodicals, Inc.

Magnetic resonance microscopy of chemically fixed human embryos at high spatial resolution

We acquired magnetic resonance (MR) microscopic images of chemically fixed human embryos of Carnegie stages 16 to 22 with a large image matrix (256 × 256 × 512) using an MR microscope that we developed with a 9.4-tesla vertical wide-bore superconducting magnet and a dual-channel receiver system to extend the dynamic range of the MR signal. The images showed clear anatomical structures at spatial resolutions of (40 µm)(3) to (60 µm)(3). We concluded that the experimental technique we developed will aid construction of the next anatomical database of the collection of chemically fixed human embryos.

Morphogenesis of the spleen during the human embryonic period

We aimed to observe morphological changes in the spleen from the emergence of the primordium to the end of the embryonic period using histological serial sections of 228 samples. Between Carnegie stages (CSs) 14 and 17, the spleen was usually recognized as a bulge in the dorsal mesogastrium (DM), and after CS 20, the spleen became apparent. Intrasplenic folds were observed later. A high-density area was first recognized in 6 of the 58 cases at CS 16 and in all cases examined after CS 18. The spleen was recognized neither as a bulge nor as a high-density area at CS 13. The mesothelium was pseudostratified until CS 16 and was replaced with high columnar cells and then with low columnar cells. The basement membrane was obvious after CS 17. The mesenchymal cells differentiated from cells in the DM, and sinus formation started at CS 20. Hematopoietic cells were detected after CS 18. The vessels were observed at CS 14 in the DM. Hilus formation was observed after CS 20. The parallel entries of the arteries and veins were observed at CS 23. The rate of increase in spleen length in relation to that of stomach length along the cranial-caudal direction was 0.51 ± 0.11, which remained constant during CSs 19 and 23, indicating that their growths were similar. These data may help to better understand the development of normal human embryos and to detect abnormal embryos in the early stages of development.