Determinants of midgut loop formation: Influence of midgut length, diameter, and location

The midgut forms tertiary loops in the extraembryonic coelom, where biomechanical factors are thought to influence this process. The number of loops may stabilize once the midgut returns to the abdominal cavity. We therefore examined how midgut length and diameter affect the number of tertiary loops before and after intestinal return.

Magnetic resonance images from 50 human embryo and fetus specimens and serial tissue sections from six fetuses were analyzed. The midgut was divided into four segments, and the length of each segment and the tube diameter at a representative central loop were measured and subjected to regression analysis. In the extraembryonic coelom, loop number increased linearly with midgut length, whereas diameter showed no independent association. In the abdominal cavity, greater length was associated with more loops, whereas greater diameter tended to be associated with fewer loops, particularly in Segment-2 and Segment-4. This pattern may be related to the apparent attenuation of further loop increase after return to the abdominal cavity during later fetal development.

The effects of midgut length and diameter on tertiary loop formation differ between the extraembryonic coelom and the abdominal cavity, highlighting the importance of midgut position in loop formation.