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Development of the arterial system
Dorsal aorta
In the third week of gestation, the right and left aortic arches turn caudally to form the corresponding dorsal (descending) aortas . These connect with the vitelline artery over the yolk sac . The first of the longitudinal veins, the postcardinal veins, develop ventrally. The intersegmental arteries branch from each aorta ( Fig. 1-1 ). A week later, the two dorsal aortas fuse to form the single dorsal (descending) aorta so that by 8 weeks, a single aortic arch and dorsal aorta are in place.
Segmental arteries
The dorsal aorta at each dermatome gives off a pair of intersegmental arteries, the dorsal somatic arteries . Each of these arteries has a dorsal branch supplying the vertebral region and neural tube and a ventral branch having lateral and terminal branches to supply the body wall ( Fig. 1-2 ). The posterior intercostal, subcostal, and lumbar arteries are derived from the dorsal somatic arteries. The enlarged 5th lumbar intersegmental artery, as the common iliac artery, will provide the blood supply to the pelvis and lower extremities.
Two other sets of segmental arteries are formed: (1) the ventral splanchnic arteries that extend to the yolk sac and gut and (2) the lateral splanchnic arteries that supply the urogenital system. After the dorsal aortas have fused, the paired ventral splanchnic arteries combine to form the celiac trunk and the superior and inferior mesenteric arteries. The lateral splanchnic arteries supply the mesonephros (and also the adult kidney) and the genital ridge , including the testis or ovary, and part of the adrenal gland.
Development of the vasculature of the body wall
The segmental vasculature develops deep to the muscles of the body wall, following the pattern of the segmental nerves. At 5 weeks, the descending aorta gives off 30 pairs of dorsal segmental arteries , 1 pair at each dermatome. These have a dorsal branch supplying the vertebral region and neural tube and a ventral branch that, in turn, has lateral and terminal branches. These branches supply the major muscles of the trunk and overlying skin by way of the intercostal, subcostal, and lumbar arteries. The more anterior portion of the body wall is supplied by a “ventral aorta” through anastomotic arteries, which will form the internal mammary and superior and inferior epigastric arteries ( Fig. 1-3 ).
From the segmentally arranged vessels such as the intercostal or lumbar arteries , branches run perpendicularly through the muscle as perforators to the skin, where they become cutaneous vessels .
Umbilical artery
The umbilical arteries originate as ventral branches of the paired dorsal aortas and enter the umbilical cord lateral to the allantois ( Fig. 1-4 A,B).
