胚子期、消化管は大きい肝臓に押し出され臍帯内に脱出すると言われています。この機序は、発生の大家Mall博士が19世紀末に提唱し、今多くの教科書に記されています。そうしたら、肝臓形成不全で肝臓が小さい胚子、肝臓がない胚子ではどうなのでしょうか？
- 本研究では、消化管臍帯ヘルニアが肝臓の容積に関係なく発生することを示す標本を複数提示することで、発生の大家の提示した説に異議を唱えました。
Kanahashi T, Yamada S, Yoneyama A, Takakuwa T. Relationship Between Physiological Umbilical Herniation and Liver Morphogenesis During the Human Embryonic Period: A Morphological and Morphometric Study. Anat Rec 2019, 302, 1968-1976. doi: 10.1002/ar.24149.
ABSTRACT
It is widely hypothesized that physiological umbilical herniation (PUH) in humans occurs, because the liver occupies a large space in the abdominal cavity, which pushes the intestine into the extraembryonic coelom during the embryonic period. We have recently shown the presence of the intestinal loop in the extraembryonic coelom in embryos with liver malformation. Here, we analyzed the relationship between the liver and the PUH at Carnegie stage 21 of four embryos with liver malformation, including two with hypogenesis (HY1, HY2) and two with agenesis (AG1, AG2), using phase-contrast X-ray computed tomography and compared them with two control embryos. The intestinal loop morphology in the malformed embryos differed from that in the control embryos, except in HY1. The length of the digestive tract in the extraembryonic coelom of the embryos with liver malformation was similar to or longer than that of the controls. The rate of intestinal loop lengthening in the extraembryonic coelom compared with that of the total digestive tract in all embryos with liver malformation was similar to or higher than that of the controls. The estimated total abdominal cavity volume in the embryos with liver malformation was considerably smaller than that of the controls, while the intestinal volume was similar. The cardia and proximal portion of the pancreas connecting to the duodenum were located at almost identical positions in all the embryos, whereas other parts of the upper digestive tract deviated in the embryos with abnormal livers. Thus, our results provided evidence that PUH occurred independently of liver volume.