Supplementary Material for: Superior mesenteric artery during intestinal loop formation and its positional changes from the extracoelom to the abdominal cavity

Introduction: Features of the superior mesenteric artery (SMA) and its intestinal branches during the embryonic and early fetal periods have not been fully described. We aimed to comprehensively elucidate the characteristics of intestinal branch artery formation in the SMA.
Methods: Serial tissue sections of seven early fetal specimens belonging to the Blechschmidt Collection were digitalized and used for segmentation and reconstruction of the intestinal loop, SMA trunk, intestinal branch arteries, and mesentery for further analysis.
Results: The intestinal branch arteries fed the intestinal tract from the oral side to the anal side, according to the order of their origin from the root to the periphery of the SMA trunk. SMA and intestinal branches were not as strongly conserved in their morphology as indicated in previous research but varied between specimens. Most intestinal branch arteries exhibited frequent branching with small intervals at the periphery, whereas the proximal branch exhibited few branches. Only a few peripheral branches made contact with the neighboring intestinal branch arteries. The fetal intestinal branch artery architecture differed greatly from that of adults. There were considerable inter- and intra-specimen variations in the intestinal tract length per feeding intestinal branch artery. The SMA branching arteries did not always supply each tertiary loop individually, and not every loop is connected to one artery.
Conclusion: This study elucidates the characteristics of forming the SMA intestinal branch arteries. Specifically, the findings suggest that the SMA is similar to other arteries in that its branches show a level of variability in feeding tissues.