In situ morphology of the aorta and common iliac artery in the fetal and neonatal rat.

In situ cross-sectional morphology of the ascending, descending, and abdominal aorta and the common iliac arteries was studied after rapid, whole-body freezing of fetal and neonatal rats. In the fetus, the ascending aorta was smaller than the descending aorta and the abdominal aorta was relatively large, continuing to the large right common iliac artery and the umbilical artery. After birth, the umbilical artery and the ductus arteriosus closed rapidly, and the size of the aorta changed within a few days. The ascending aorta became larger than the descending aorta in 2 d, and the abdominal aorta became smaller, especially at the infrarenal part. The right common iliac artery, which continues to the umbilical artery in fetal life, became smaller, and its diameter was the same as that of the left common iliac artery 2 d after birth.