Chapter 123. Development of The Arterial System - Review of Medical Embryology Book

The arterial system: the primitive arterial system undergoes numerous modifications in its development, which are minimal in the embryonic posterior region, basic in its middle region where fusion of the 2 aortas forms a single aorta, and quite complex in the anterior region where the aortic arches are formed

The paired umbilical arteries arise from the dorsal aorta at the posterior end of the ventral segmental arteries

The umbilical arteries remain paired during the growth of the embryo, although their point of origin moves slightly in a caudal direction, and they do give off a small external branch to the lower limbs
When placental circulation is interrupted at birth, the umbilical arteries become fibrosed over most of their length. Their proximal portion gives rise to the primitive iliac, hypogastric, and superior vesical arteries. The branch to the lower limb becomes the external iliac artery

The 2 dorsal aortas approach each other and fuse at about week They fuse initially in the middle portion, then cranially up to the eighth segmental artery and caudally to the posterior en By the middle of week 5, the single dorsal aorta is formed
The paired ventral segmental arteries approach each other in the midline in the mesentery, and some fuse into median vessels creating 3 visceral arterial systems

The celiac trunk
The superior mesenteric artery, which is derived from a special segmental artery, the omphalomensenteric artery, after regression of its vitelline portion (the left one disappears entirely)
The inferior mesenteric artery

Temporary longitudinal anastomoses result in the caudal movement of the origins of the above arteries, and they reach their final levels at about the end of month 2
The dorsal segmental arteries remain unpaired (in contrast to the ventral). Initially, they only supply the neural tub Their somatic branches, however, grow considerably and finally predominat Some of the dorsal segmental arteries persist to form the intercostal arteries
The lateral segmental arteries, which exist in two symmetric series, provide vascularization to the mesonephros and the gonads

Six pairs of aortic arches are theoretically formed; however, the fifth pair is essentially only a temporary doubling of the fourth pair
The aortic arches form successively, thus are never all present at the same time

The aortic arches arise from the dilated region of the truncus arteriosus, known as the aortic sac, and terminate in the dorsal aorta of the corresponding side
During weeks 6 to 8, the primitive aortic arch pattern is transformed into the basic adult arterial arrangement