Gut formation after transection of the midgut loop in the chick embryo

The primitive gut in vertebrates can be divided into the foregut, midgut, and hindgut. The midgut forms the midgut loop or the intestinal loop, which rotates as it develops the small and large intestines. We examined the effects of transection of the midgut loop on the subsequent development of the intestine in chick embryos by their out-of-the-shell incubation. The development of the embryo and the intestines out of the shell was nearly identical to that usual in-the-shell incubation. The rotation of the midgut loop began in stage 27 (5 days of incubation) and was completed in stage 36 (10 days of incubation) after counterclockwise rotation through 180 degrees. In experimental groups, the midgut loop was transected immediately before or in the early stages of rotation (stages 27-33) proximally or distally to the apex of the loop. Transecting of the midgut loop caused little effects on its subsequent rotation regardless of the time or the site of transection although the secondary loop formation of intestine was poor in some cases. The stumps of the transected intestine were repaired and closed. After closure of the stumps, the proximal segment of the intestine was dilated in some cases. The secondary loop formation, or convolution of the intestine didn't occur in some dilated cases.