Iliac Arteries
The common iliac arteries, each a continuation of the descending aorta, arise from the bifurcation (splitting into two) of the abdominal aorta at about the level of the fourth lumbar vertebra. The common iliac arteries bifurcate again into internal and external iliac arteries that supply oxygenated blood to the lower abdomen, pelvis, and legs.
On both the left and right sides, the common iliac artery is short, and each common iliac artery divides into an internal and an external iliac artery at about the level of the sacrum. Before bifurcating into internal and external iliac arteries, it gives rise to small branches that supply blood to the ureter and peritoneal structures. The external iliac arteries continue on to supply blood to the legs (lower limb) and the internal iliac arteries supply blood to pelvic and peritoneal structure.
The internal iliac arteries are prominent in the fetus and can be twice the size of the external iliac arteries. The reason for this size difference lies in the fact that the internal iliac arteries run to the abdominal wall and then turn superiorly (upward) to eventually fuse at the umbilicus (in the adult, the "navel" or "belly button" region). The continuation of the fused internal iliacs in the umbilical cord becomes the umbilical artery that ultimately branches into the placenta.
Following birth, the interruption of blood flow through the umbilical cord causes the portion of the internal iliacs that continue to the umbilicus to close. Ultimately, what was once an umbilical extension of the internal iliac artery becomes the fibrous medial umbilical ligament.
The internal iliac arteries divide into anterior and posterior trunks. In the adult, major branches of the internal iliac arteries supply blood to the bladder, ureter, and other pelvic structures. In the male, the internal iliac branches supply a portion of the arterial blood to the testis and prostate. In the female, oxygenated blood from the internal iliacs also supplies the vagina and uterus. In both males and females, braches of the internal iliac arteries supply blood to the external genitalia.
In the adult, the external iliac arteries are larger than the internal iliac arteries. The external iliac arteries become the large diameter femoral arteries that supply blood to the legs. Before becoming the femoral arteries, the external iliacs give rise to a few branches, including the inferior epigastric and deep circumflex iliac arteries that fuse (anastomose) with other arteries and thereby allow the development of collateral circulation to the leg in the event of interruption in the normal supply of blood through the common iliac artery.
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